From a47f6d2bfc44b5bae36ac5001a46f6b6c045f9d9 Mon Sep 17 00:00:00 2001
From: Raif Atef <beliskner.github.3psil0N@neverbox.com>
Date: Thu, 17 Nov 2016 01:05:44 +0200
Subject: [PATCH] Refresh tokens when needed instead of logging out when
 access_token expires.

- refresh_token + access_token expiry is sent via encrypted cookie to the browser.
- If cookie is missing or invalid, user is logged out.
- If last access token expired, use refresh token to fetch a new one and send a new cookie.
- If token refresh fails, user is logged out.
- Cookie encryption is with per-user random key stored in user meta.
- Encryption and key generation done using https://github.com/defuse/php-encryption
- Updated autoloader function to support loading namespaced classes.
---
 includes/Defuse/Crypto/Core.php               | 434 ++++++++++
 includes/Defuse/Crypto/Crypto.php             | 372 +++++++++
 includes/Defuse/Crypto/DerivedKeys.php        |  37 +
 includes/Defuse/Crypto/Encoding.php           | 212 +++++
 .../Crypto/Exception/BadFormatException.php   |   7 +
 .../Crypto/Exception/CryptoException.php      |   7 +
 .../EnvironmentIsBrokenException.php          |   7 +
 .../Defuse/Crypto/Exception/IOException.php   |   7 +
 .../WrongKeyOrModifiedCiphertextException.php |   7 +
 includes/Defuse/Crypto/File.php               | 755 ++++++++++++++++++
 includes/Defuse/Crypto/Key.php                |  84 ++
 includes/Defuse/Crypto/KeyOrPassword.php      | 119 +++
 .../Defuse/Crypto/KeyProtectedByPassword.php  | 112 +++
 includes/Defuse/Crypto/RuntimeTests.php       | 242 ++++++
 .../openid-connect-generic-client-wrapper.php | 106 ++-
 includes/openid-connect-generic-client.php    |  38 +
 openid-connect-generic.php                    |   9 +-
 17 files changed, 2537 insertions(+), 18 deletions(-)
 create mode 100644 includes/Defuse/Crypto/Core.php
 create mode 100644 includes/Defuse/Crypto/Crypto.php
 create mode 100644 includes/Defuse/Crypto/DerivedKeys.php
 create mode 100644 includes/Defuse/Crypto/Encoding.php
 create mode 100644 includes/Defuse/Crypto/Exception/BadFormatException.php
 create mode 100644 includes/Defuse/Crypto/Exception/CryptoException.php
 create mode 100644 includes/Defuse/Crypto/Exception/EnvironmentIsBrokenException.php
 create mode 100644 includes/Defuse/Crypto/Exception/IOException.php
 create mode 100644 includes/Defuse/Crypto/Exception/WrongKeyOrModifiedCiphertextException.php
 create mode 100644 includes/Defuse/Crypto/File.php
 create mode 100644 includes/Defuse/Crypto/Key.php
 create mode 100644 includes/Defuse/Crypto/KeyOrPassword.php
 create mode 100644 includes/Defuse/Crypto/KeyProtectedByPassword.php
 create mode 100644 includes/Defuse/Crypto/RuntimeTests.php

diff --git a/includes/Defuse/Crypto/Core.php b/includes/Defuse/Crypto/Core.php
new file mode 100644
index 0000000..c489f39
--- /dev/null
+++ b/includes/Defuse/Crypto/Core.php
@@ -0,0 +1,434 @@
+<?php
+
+namespace Defuse\Crypto;
+
+use Defuse\Crypto\Exception as Ex;
+
+final class Core
+{
+    const HEADER_VERSION_SIZE               = 4;
+    const MINIMUM_CIPHERTEXT_SIZE           = 84;
+
+    const CURRENT_VERSION                   = "\xDE\xF5\x02\x00";
+
+    const CIPHER_METHOD                     = 'aes-256-ctr';
+    const BLOCK_BYTE_SIZE                   = 16;
+    const KEY_BYTE_SIZE                     = 32;
+    const SALT_BYTE_SIZE                    = 32;
+    const MAC_BYTE_SIZE                     = 32;
+    const HASH_FUNCTION_NAME                = 'sha256';
+    const ENCRYPTION_INFO_STRING            = 'DefusePHP|V2|KeyForEncryption';
+    const AUTHENTICATION_INFO_STRING        = 'DefusePHP|V2|KeyForAuthentication';
+    const BUFFER_BYTE_SIZE                  = 1048576;
+
+    const LEGACY_CIPHER_METHOD              = 'aes-128-cbc';
+    const LEGACY_BLOCK_BYTE_SIZE            = 16;
+    const LEGACY_KEY_BYTE_SIZE              = 16;
+    const LEGACY_HASH_FUNCTION_NAME         = 'sha256';
+    const LEGACY_MAC_BYTE_SIZE              = 32;
+    const LEGACY_ENCRYPTION_INFO_STRING     = 'DefusePHP|KeyForEncryption';
+    const LEGACY_AUTHENTICATION_INFO_STRING = 'DefusePHP|KeyForAuthentication';
+
+    /*
+     * V2.0 Format: VERSION (4 bytes) || SALT (32 bytes) || IV (16 bytes) ||
+     *              CIPHERTEXT (varies) || HMAC (32 bytes)
+     *
+     * V1.0 Format: HMAC (32 bytes) || IV (16 bytes) || CIPHERTEXT (varies).
+     */
+
+    /**
+     * Adds an integer to a block-sized counter.
+     *
+     * @param string $ctr
+     * @param int    $inc
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     *
+     * @return string
+     */
+    public static function incrementCounter($ctr, $inc)
+    {
+        if (Core::ourStrlen($ctr) !== Core::BLOCK_BYTE_SIZE) {
+            throw new Ex\EnvironmentIsBrokenException(
+              'Trying to increment a nonce of the wrong size.'
+            );
+        }
+
+        if (! \is_int($inc)) {
+            throw new Ex\EnvironmentIsBrokenException(
+              'Trying to increment nonce by a non-integer.'
+            );
+        }
+
+        if ($inc < 0) {
+            throw new Ex\EnvironmentIsBrokenException(
+              'Trying to increment nonce by a negative amount.'
+            );
+        }
+
+        if ($inc > PHP_INT_MAX - 255) {
+            throw new Ex\EnvironmentIsBrokenException(
+              'Integer overflow may occur.'
+            );
+        }
+
+        /*
+         * We start at the rightmost byte (big-endian)
+         * So, too, does OpenSSL: http://stackoverflow.com/a/3146214/2224584
+         */
+        for ($i = Core::BLOCK_BYTE_SIZE - 1; $i >= 0; --$i) {
+            $sum = \ord($ctr[$i]) + $inc;
+
+            /* Detect integer overflow and fail. */
+            if (! \is_int($sum)) {
+                throw new Ex\EnvironmentIsBrokenException(
+                  'Integer overflow in CTR mode nonce increment.'
+                );
+            }
+
+            $ctr[$i] = \pack('C', $sum & 0xFF);
+            $inc     = $sum >> 8;
+        }
+        return $ctr;
+    }
+
+    /**
+     * Returns a random byte string of the specified length.
+     *
+     * @param int $octets
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     *
+     * @return string
+     */
+    public static function secureRandom($octets)
+    {
+        self::ensureFunctionExists('random_bytes');
+        try {
+            return \random_bytes($octets);
+        } catch (\Exception $ex) {
+            throw new Ex\EnvironmentIsBrokenException(
+                'Your system does not have a secure random number generator.'
+            );
+        }
+    }
+
+    /**
+     * Computes the HKDF key derivation function specified in
+     * http://tools.ietf.org/html/rfc5869.
+     *
+     * @param string $hash   Hash Function
+     * @param string $ikm    Initial Keying Material
+     * @param int    $length How many bytes?
+     * @param string $info   What sort of key are we deriving?
+     * @param string $salt
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     *
+     * @return string
+     */
+    public static function HKDF($hash, $ikm, $length, $info = '', $salt = null)
+    {
+        $digest_length = Core::ourStrlen(\hash_hmac($hash, '', '', true));
+
+        // Sanity-check the desired output length.
+        if (empty($length) || ! \is_int($length) ||
+            $length < 0 || $length > 255 * $digest_length) {
+            throw new Ex\EnvironmentIsBrokenException(
+                'Bad output length requested of HKDF.'
+            );
+        }
+
+        // "if [salt] not provided, is set to a string of HashLen zeroes."
+        if (\is_null($salt)) {
+            $salt = \str_repeat("\x00", $digest_length);
+        }
+
+        // HKDF-Extract:
+        // PRK = HMAC-Hash(salt, IKM)
+        // The salt is the HMAC key.
+        $prk = \hash_hmac($hash, $ikm, $salt, true);
+
+        // HKDF-Expand:
+
+        // This check is useless, but it serves as a reminder to the spec.
+        if (Core::ourStrlen($prk) < $digest_length) {
+            throw new Ex\EnvironmentIsBrokenException();
+        }
+
+        // T(0) = ''
+        $t          = '';
+        $last_block = '';
+        for ($block_index = 1; Core::ourStrlen($t) < $length; ++$block_index) {
+            // T(i) = HMAC-Hash(PRK, T(i-1) | info | 0x??)
+            $last_block = \hash_hmac(
+                $hash,
+                $last_block . $info . \chr($block_index),
+                $prk,
+                true
+            );
+            // T = T(1) | T(2) | T(3) | ... | T(N)
+            $t .= $last_block;
+        }
+
+        // ORM = first L octets of T
+        $orm = Core::ourSubstr($t, 0, $length);
+        if ($orm === false) {
+            throw new Ex\EnvironmentIsBrokenException();
+        }
+        return $orm;
+    }
+
+    /**
+     * Checks if two equal-length strings are the same without leaking
+     * information through side channels.
+     *
+     * @param string $expected
+     * @param string $given
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     *
+     * @return bool
+     */
+    public static function hashEquals($expected, $given)
+    {
+        static $native = null;
+        if ($native === null) {
+            $native = \function_exists('hash_equals');
+        }
+        if ($native) {
+            return \hash_equals($expected, $given);
+        }
+
+        // We can't just compare the strings with '==', since it would make
+        // timing attacks possible. We could use the XOR-OR constant-time
+        // comparison algorithm, but that may not be a reliable defense in an
+        // interpreted language. So we use the approach of HMACing both strings
+        // with a random key and comparing the HMACs.
+
+        // We're not attempting to make variable-length string comparison
+        // secure, as that's very difficult. Make sure the strings are the same
+        // length.
+        if (Core::ourStrlen($expected) !== Core::ourStrlen($given)) {
+            throw new Ex\EnvironmentIsBrokenException();
+        }
+
+        $blind           = Core::secureRandom(32);
+        $message_compare = \hash_hmac(Core::HASH_FUNCTION_NAME, $given, $blind);
+        $correct_compare = \hash_hmac(Core::HASH_FUNCTION_NAME, $expected, $blind);
+        return $correct_compare === $message_compare;
+    }
+    /**
+     * Throws an exception if the constant doesn't exist.
+     *
+     * @param string $name
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     */
+    public static function ensureConstantExists($name)
+    {
+        if (! \defined($name)) {
+            throw new Ex\EnvironmentIsBrokenException();
+        }
+    }
+
+    /**
+     * Throws an exception if the function doesn't exist.
+     *
+     * @param string $name
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     */
+    public static function ensureFunctionExists($name)
+    {
+        if (! \function_exists($name)) {
+            throw new Ex\EnvironmentIsBrokenException();
+        }
+    }
+
+    /*
+     * We need these strlen() and substr() functions because when
+     * 'mbstring.func_overload' is set in php.ini, the standard strlen() and
+     * substr() are replaced by mb_strlen() and mb_substr().
+     */
+
+    /**
+     * Computes the length of a string in bytes.
+     *
+     * @param string $str
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     *
+     * @return int
+     */
+    public static function ourStrlen($str)
+    {
+        static $exists = null;
+        if ($exists === null) {
+            $exists = \function_exists('mb_strlen');
+        }
+        if ($exists) {
+            $length = \mb_strlen($str, '8bit');
+            if ($length === false) {
+                throw new Ex\EnvironmentIsBrokenException();
+            }
+            return $length;
+        } else {
+            return \strlen($str);
+        }
+    }
+
+    /**
+     * Behaves roughly like the function substr() in PHP 7 does.
+     *
+     * @param string $str
+     * @param int    $start
+     * @param int    $length
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     *
+     * @return string
+     */
+    public static function ourSubstr($str, $start, $length = null)
+    {
+        static $exists = null;
+        if ($exists === null) {
+            $exists = \function_exists('mb_substr');
+        }
+
+        if ($exists) {
+            // mb_substr($str, 0, NULL, '8bit') returns an empty string on PHP
+            // 5.3, so we have to find the length ourselves.
+            if (! isset($length)) {
+                if ($start >= 0) {
+                    $length = Core::ourStrlen($str) - $start;
+                } else {
+                    $length = -$start;
+                }
+            }
+
+            // This is required to make mb_substr behavior identical to substr.
+            // Without this, mb_substr() would return false, contra to what the
+            // PHP documentation says (it doesn't say it can return false.)
+            if ($start === Core::ourStrlen($str) && $length === 0) {
+                return '';
+            }
+
+            if ($start > Core::ourStrlen($str)) {
+                return false;
+            }
+
+            $substr = \mb_substr($str, $start, $length, '8bit');
+            if (Core::ourStrlen($substr) !== $length) {
+                throw new Ex\EnvironmentIsBrokenException(
+                    'Your version of PHP has bug #66797. Its implementation of
+                    mb_substr() is incorrect. See the details here:
+                    https://bugs.php.net/bug.php?id=66797'
+                );
+            }
+            return $substr;
+        }
+
+        // Unlike mb_substr(), substr() doesn't accept NULL for length
+        if (isset($length)) {
+            return \substr($str, $start, $length);
+        } else {
+            return \substr($str, $start);
+        }
+    }
+
+    /**
+     * Computes the PBKDF2 password-based key derivation function.
+     *
+     * The PBKDF2 function is defined in RFC 2898. Test vectors can be found in
+     * RFC 6070. This implementation of PBKDF2 was originally created by Taylor
+     * Hornby, with improvements from http://www.variations-of-shadow.com/.
+     *
+     * @param string $algorithm  The hash algorithm to use. Recommended: SHA256
+     * @param string $password   The password.
+     * @param string $salt       A salt that is unique to the password.
+     * @param int    $count      Iteration count. Higher is better, but slower. Recommended: At least 1000.
+     * @param int    $key_length The length of the derived key in bytes.
+     * @param bool   $raw_output If true, the key is returned in raw binary format. Hex encoded otherwise.
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     *
+     * @return string A $key_length-byte key derived from the password and salt.
+     */
+    public static function pbkdf2($algorithm, $password, $salt, $count, $key_length, $raw_output = false)
+    {
+        // Type checks:
+        if (! \is_string($algorithm)) {
+            throw new \InvalidArgumentException(
+                'pbkdf2(): algorithm must be a string'
+            );
+        }
+        if (! \is_string($password)) {
+            throw new \InvalidArgumentException(
+                'pbkdf2(): password must be a string'
+            );
+        }
+        if (! \is_string($salt)) {
+            throw new \InvalidArgumentException(
+                'pbkdf2(): salt must be a string'
+            );
+        }
+        // Coerce strings to integers with no information loss or overflow
+        $count += 0;
+        $key_length += 0;
+
+        $algorithm = \strtolower($algorithm);
+        if (! \in_array($algorithm, \hash_algos(), true)) {
+            throw new Ex\EnvironmentIsBrokenException(
+                'Invalid or unsupported hash algorithm.'
+            );
+        }
+
+        // Whitelist, or we could end up with people using CRC32.
+        $ok_algorithms = [
+            'sha1', 'sha224', 'sha256', 'sha384', 'sha512',
+            'ripemd160', 'ripemd256', 'ripemd320', 'whirlpool',
+        ];
+        if (! \in_array($algorithm, $ok_algorithms, true)) {
+            throw new Ex\EnvironmentIsBrokenException(
+                'Algorithm is not a secure cryptographic hash function.'
+            );
+        }
+
+        if ($count <= 0 || $key_length <= 0) {
+            throw new Ex\EnvironmentIsBrokenException(
+                'Invalid PBKDF2 parameters.'
+            );
+        }
+
+        if (\function_exists('hash_pbkdf2')) {
+            // The output length is in NIBBLES (4-bits) if $raw_output is false!
+            if (! $raw_output) {
+                $key_length = $key_length * 2;
+            }
+            return \hash_pbkdf2($algorithm, $password, $salt, $count, $key_length, $raw_output);
+        }
+
+        $hash_length = Core::ourStrlen(\hash($algorithm, '', true));
+        $block_count = \ceil($key_length / $hash_length);
+
+        $output = '';
+        for ($i = 1; $i <= $block_count; $i++) {
+            // $i encoded as 4 bytes, big endian.
+            $last = $salt . \pack('N', $i);
+            // first iteration
+            $last = $xorsum = \hash_hmac($algorithm, $last, $password, true);
+            // perform the other $count - 1 iterations
+            for ($j = 1; $j < $count; $j++) {
+                $xorsum ^= ($last = \hash_hmac($algorithm, $last, $password, true));
+            }
+            $output .= $xorsum;
+        }
+
+        if ($raw_output) {
+            return Core::ourSubstr($output, 0, $key_length);
+        } else {
+            return Encoding::binToHex(Core::ourSubstr($output, 0, $key_length));
+        }
+    }
+}
diff --git a/includes/Defuse/Crypto/Crypto.php b/includes/Defuse/Crypto/Crypto.php
new file mode 100644
index 0000000..3acd611
--- /dev/null
+++ b/includes/Defuse/Crypto/Crypto.php
@@ -0,0 +1,372 @@
+<?php
+
+namespace Defuse\Crypto;
+
+use Defuse\Crypto\Exception as Ex;
+
+class Crypto
+{
+    /**
+     * Encrypts a string with a Key.
+     *
+     * @param string $plaintext
+     * @param Key    $key
+     * @param bool   $raw_binary
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     *
+     * @return string
+     */
+    public static function encrypt($plaintext, Key $key, $raw_binary = false)
+    {
+        return self::encryptInternal(
+            $plaintext,
+            KeyOrPassword::createFromKey($key),
+            $raw_binary
+        );
+    }
+
+    /**
+     * Encrypts a string with a password, using a slow key derivation function
+     * to make password cracking more expensive.
+     *
+     * @param string $plaintext
+     * @param string $password
+     * @param bool   $raw_binary
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     *
+     * @return string
+     */
+    public static function encryptWithPassword($plaintext, $password, $raw_binary = false)
+    {
+        return self::encryptInternal(
+            $plaintext,
+            KeyOrPassword::createFromPassword($password),
+            $raw_binary
+        );
+    }
+
+    /**
+     * Decrypts a ciphertext to a string with a Key.
+     *
+     * @param string $ciphertext
+     * @param Key    $key
+     * @param bool   $raw_binary
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     * @throws Ex\WrongKeyOrModifiedCiphertextException
+     *
+     * @return string
+     */
+    public static function decrypt($ciphertext, Key $key, $raw_binary = false)
+    {
+        return self::decryptInternal(
+            $ciphertext,
+            KeyOrPassword::createFromKey($key),
+            $raw_binary
+        );
+    }
+
+    /**
+     * Decrypts a ciphertext to a string with a password, using a slow key
+     * derivation function to make password cracking more expensive.
+     *
+     * @param string $ciphertext
+     * @param string $password
+     * @param bool   $raw_binary
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     * @throws Ex\WrongKeyOrModifiedCiphertextException
+     *
+     * @return string
+     */
+    public static function decryptWithPassword($ciphertext, $password, $raw_binary = false)
+    {
+        return self::decryptInternal(
+            $ciphertext,
+            KeyOrPassword::createFromPassword($password),
+            $raw_binary
+        );
+    }
+
+    /**
+     * Decrypts a legacy ciphertext produced by version 1 of this library.
+     *
+     * @param string $ciphertext
+     * @param string $key
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     * @throws Ex\WrongKeyOrModifiedCiphertextException
+     *
+     * @return string
+     */
+    public static function legacyDecrypt($ciphertext, $key)
+    {
+        RuntimeTests::runtimeTest();
+
+        // Extract the HMAC from the front of the ciphertext.
+        if (Core::ourStrlen($ciphertext) <= Core::LEGACY_MAC_BYTE_SIZE) {
+            throw new Ex\WrongKeyOrModifiedCiphertextException(
+                'Ciphertext is too short.'
+            );
+        }
+        $hmac = Core::ourSubstr($ciphertext, 0, Core::LEGACY_MAC_BYTE_SIZE);
+        if ($hmac === false) {
+            throw new Ex\EnvironmentIsBrokenException();
+        }
+        $ciphertext = Core::ourSubstr($ciphertext, Core::LEGACY_MAC_BYTE_SIZE);
+        if ($ciphertext === false) {
+            throw new Ex\EnvironmentIsBrokenException();
+        }
+
+        // Regenerate the same authentication sub-key.
+        $akey = Core::HKDF(
+            Core::LEGACY_HASH_FUNCTION_NAME,
+            $key,
+            Core::LEGACY_KEY_BYTE_SIZE,
+            Core::LEGACY_AUTHENTICATION_INFO_STRING,
+            null
+        );
+
+        if (self::verifyHMAC($hmac, $ciphertext, $akey)) {
+            // Regenerate the same encryption sub-key.
+            $ekey = Core::HKDF(
+                Core::LEGACY_HASH_FUNCTION_NAME,
+                $key,
+                Core::LEGACY_KEY_BYTE_SIZE,
+                Core::LEGACY_ENCRYPTION_INFO_STRING,
+                null
+            );
+
+            // Extract the IV from the ciphertext.
+            if (Core::ourStrlen($ciphertext) <= Core::LEGACY_BLOCK_BYTE_SIZE) {
+                throw new Ex\WrongKeyOrModifiedCiphertextException(
+                    'Ciphertext is too short.'
+                );
+            }
+            $iv = Core::ourSubstr($ciphertext, 0, Core::LEGACY_BLOCK_BYTE_SIZE);
+            if ($iv === false) {
+                throw new Ex\EnvironmentIsBrokenException();
+            }
+            $ciphertext = Core::ourSubstr($ciphertext, Core::LEGACY_BLOCK_BYTE_SIZE);
+            if ($ciphertext === false) {
+                throw new Ex\EnvironmentIsBrokenException();
+            }
+
+            // Do the decryption.
+            $plaintext = self::plainDecrypt($ciphertext, $ekey, $iv, Core::LEGACY_CIPHER_METHOD);
+            return $plaintext;
+        } else {
+            throw new Ex\WrongKeyOrModifiedCiphertextException(
+                'Integrity check failed.'
+            );
+        }
+    }
+
+    /**
+     * Encrypts a string with either a key or a password.
+     *
+     * @param string        $plaintext
+     * @param KeyOrPassword $secret
+     * @param bool          $raw_binary
+     *
+     * @return string
+     */
+    private static function encryptInternal($plaintext, KeyOrPassword $secret, $raw_binary)
+    {
+        RuntimeTests::runtimeTest();
+
+        $salt = Core::secureRandom(Core::SALT_BYTE_SIZE);
+        $keys = $secret->deriveKeys($salt);
+        $ekey = $keys->getEncryptionKey();
+        $akey = $keys->getAuthenticationKey();
+        $iv     = Core::secureRandom(Core::BLOCK_BYTE_SIZE);
+
+        $ciphertext = Core::CURRENT_VERSION . $salt . $iv . self::plainEncrypt($plaintext, $ekey, $iv);
+        $auth       = \hash_hmac(Core::HASH_FUNCTION_NAME, $ciphertext, $akey, true);
+        $ciphertext = $ciphertext . $auth;
+
+        if ($raw_binary) {
+            return $ciphertext;
+        }
+        return Encoding::binToHex($ciphertext);
+    }
+
+    /**
+     * Decrypts a ciphertext to a string with either a key or a password.
+     *
+     * @param string        $ciphertext
+     * @param KeyOrPassword $secret
+     * @param bool          $raw_binary
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     * @throws Ex\WrongKeyOrModifiedCiphertextException
+     *
+     * @return string
+     */
+    private static function decryptInternal($ciphertext, KeyOrPassword $secret, $raw_binary)
+    {
+        RuntimeTests::runtimeTest();
+
+        if (! $raw_binary) {
+            try {
+                $ciphertext = Encoding::hexToBin($ciphertext);
+            } catch (Ex\BadFormatException $ex) {
+                throw new Ex\WrongKeyOrModifiedCiphertextException(
+                    'Ciphertext has invalid hex encoding.'
+                );
+            }
+        }
+
+        if (Core::ourStrlen($ciphertext) < Core::MINIMUM_CIPHERTEXT_SIZE) {
+            throw new Ex\WrongKeyOrModifiedCiphertextException(
+                'Ciphertext is too short.'
+            );
+        }
+
+        // Get and check the version header.
+        $header = Core::ourSubstr($ciphertext, 0, Core::HEADER_VERSION_SIZE);
+        if ($header !== Core::CURRENT_VERSION) {
+            throw new Ex\WrongKeyOrModifiedCiphertextException(
+                'Bad version header.'
+            );
+        }
+
+        // Get the salt.
+        $salt = Core::ourSubstr(
+            $ciphertext,
+            Core::HEADER_VERSION_SIZE,
+            Core::SALT_BYTE_SIZE
+        );
+        if ($salt === false) {
+            throw new Ex\EnvironmentIsBrokenException();
+        }
+
+        // Get the IV.
+        $iv = Core::ourSubstr(
+            $ciphertext,
+            Core::HEADER_VERSION_SIZE + Core::SALT_BYTE_SIZE,
+            Core::BLOCK_BYTE_SIZE
+        );
+        if ($iv === false) {
+            throw new Ex\EnvironmentIsBrokenException();
+        }
+
+        // Get the HMAC.
+        $hmac = Core::ourSubstr(
+            $ciphertext,
+            Core::ourStrlen($ciphertext) - Core::MAC_BYTE_SIZE,
+            Core::MAC_BYTE_SIZE
+        );
+        if ($hmac === false) {
+            throw new Ex\EnvironmentIsBrokenException();
+        }
+
+        // Get the actual encrypted ciphertext.
+        $encrypted = Core::ourSubstr(
+            $ciphertext,
+            Core::HEADER_VERSION_SIZE + Core::SALT_BYTE_SIZE +
+                Core::BLOCK_BYTE_SIZE,
+            Core::ourStrlen($ciphertext) - Core::MAC_BYTE_SIZE - Core::SALT_BYTE_SIZE -
+                Core::BLOCK_BYTE_SIZE - Core::HEADER_VERSION_SIZE
+        );
+        if ($encrypted === false) {
+            throw new Ex\EnvironmentIsBrokenException();
+        }
+
+        // Derive the separate encryption and authentication keys from the key
+        // or password, whichever it is.
+        $keys = $secret->deriveKeys($salt);
+
+        if (self::verifyHMAC($hmac, $header . $salt . $iv . $encrypted, $keys->getAuthenticationKey())) {
+            $plaintext = self::plainDecrypt($encrypted, $keys->getEncryptionKey(), $iv, Core::CIPHER_METHOD);
+            return $plaintext;
+        } else {
+            throw new Ex\WrongKeyOrModifiedCiphertextException(
+                'Integrity check failed.'
+            );
+        }
+    }
+
+    /**
+     * Raw unauthenticated encryption (insecure on its own).
+     *
+     * @param string $plaintext
+     * @param string $key
+     * @param string $iv
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     *
+     * @return string
+     */
+    protected static function plainEncrypt($plaintext, $key, $iv)
+    {
+        Core::ensureConstantExists('OPENSSL_RAW_DATA');
+        Core::ensureFunctionExists('openssl_encrypt');
+        $ciphertext = \openssl_encrypt(
+            $plaintext,
+            Core::CIPHER_METHOD,
+            $key,
+            OPENSSL_RAW_DATA,
+            $iv
+        );
+
+        if ($ciphertext === false) {
+            throw new Ex\EnvironmentIsBrokenException(
+                'openssl_encrypt() failed.'
+            );
+        }
+
+        return $ciphertext;
+    }
+
+    /**
+     * Raw unauthenticated decryption (insecure on its own).
+     *
+     * @param string $ciphertext
+     * @param string $key
+     * @param string $iv
+     * @param string $cipherMethod
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     *
+     * @return string
+     */
+    protected static function plainDecrypt($ciphertext, $key, $iv, $cipherMethod)
+    {
+        Core::ensureConstantExists('OPENSSL_RAW_DATA');
+        Core::ensureFunctionExists('openssl_decrypt');
+        $plaintext = \openssl_decrypt(
+            $ciphertext,
+            $cipherMethod,
+            $key,
+            OPENSSL_RAW_DATA,
+            $iv
+        );
+        if ($plaintext === false) {
+            throw new Ex\EnvironmentIsBrokenException(
+                'openssl_decrypt() failed.'
+            );
+        }
+
+        return $plaintext;
+    }
+
+    /**
+     * Verifies an HMAC without leaking information through side-channels.
+     *
+     * @param string $correct_hmac
+     * @param string $message
+     * @param string $key
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     *
+     * @return bool
+     */
+    protected static function verifyHMAC($correct_hmac, $message, $key)
+    {
+        $message_hmac = \hash_hmac(Core::HASH_FUNCTION_NAME, $message, $key, true);
+        return Core::hashEquals($correct_hmac, $message_hmac);
+    }
+}
diff --git a/includes/Defuse/Crypto/DerivedKeys.php b/includes/Defuse/Crypto/DerivedKeys.php
new file mode 100644
index 0000000..fcfc043
--- /dev/null
+++ b/includes/Defuse/Crypto/DerivedKeys.php
@@ -0,0 +1,37 @@
+<?php
+
+namespace Defuse\Crypto;
+
+final class DerivedKeys
+{
+    private $akey = null;
+    private $ekey = null;
+
+    /**
+     * Returns the authentication key.
+     */
+    public function getAuthenticationKey()
+    {
+        return $this->akey;
+    }
+
+    /**
+     * Returns the encryption key.
+     */
+    public function getEncryptionKey()
+    {
+        return $this->ekey;
+    }
+
+    /**
+     * Constructor for DerivedKeys.
+     *
+     * @param string $akey
+     * @param string $ekey
+     */
+    public function __construct($akey, $ekey)
+    {
+        $this->akey = $akey;
+        $this->ekey = $ekey;
+    }
+}
diff --git a/includes/Defuse/Crypto/Encoding.php b/includes/Defuse/Crypto/Encoding.php
new file mode 100644
index 0000000..6e022d7
--- /dev/null
+++ b/includes/Defuse/Crypto/Encoding.php
@@ -0,0 +1,212 @@
+<?php
+
+namespace Defuse\Crypto;
+
+use Defuse\Crypto\Exception as Ex;
+
+final class Encoding
+{
+    const CHECKSUM_BYTE_SIZE     = 32;
+    const CHECKSUM_HASH_ALGO     = 'sha256';
+    const SERIALIZE_HEADER_BYTES = 4;
+
+    /**
+     * Converts a byte string to a hexadecimal string without leaking
+     * information through side channels.
+     *
+     * @param string $byte_string
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     *
+     * @return string
+     */
+    public static function binToHex($byte_string)
+    {
+        $hex = '';
+        $len = Core::ourStrlen($byte_string);
+        for ($i = 0; $i < $len; ++$i) {
+            $c = \ord($byte_string[$i]) & 0xf;
+            $b = \ord($byte_string[$i]) >> 4;
+            $hex .= \pack(
+                'CC',
+                87 + $b + ((($b - 10) >> 8) & ~38),
+                87 + $c + ((($c - 10) >> 8) & ~38)
+            );
+        }
+        return $hex;
+    }
+
+    /**
+     * Converts a hexadecimal string into a byte string without leaking
+     * information through side channels.
+     *
+     * @param string $hex_string
+     *
+     * @throws Ex\BadFormatException
+     * @throws Ex\EnvironmentIsBrokenException
+     *
+     * @return string
+     */
+    public static function hexToBin($hex_string)
+    {
+        $hex_pos = 0;
+        $bin     = '';
+        $hex_len = Core::ourStrlen($hex_string);
+        $state   = 0;
+        $c_acc   = 0;
+
+        while ($hex_pos < $hex_len) {
+            $c        = \ord($hex_string[$hex_pos]);
+            $c_num    = $c ^ 48;
+            $c_num0   = ($c_num - 10) >> 8;
+            $c_alpha  = ($c & ~32) - 55;
+            $c_alpha0 = (($c_alpha - 10) ^ ($c_alpha - 16)) >> 8;
+            if (($c_num0 | $c_alpha0) === 0) {
+                throw new Ex\BadFormatException(
+                    'Encoding::hexToBin() input is not a hex string.'
+                );
+            }
+            $c_val = ($c_num0 & $c_num) | ($c_alpha & $c_alpha0);
+            if ($state === 0) {
+                $c_acc = $c_val * 16;
+            } else {
+                $bin .= \pack('C', $c_acc | $c_val);
+            }
+            $state ^= 1;
+            ++$hex_pos;
+        }
+        return $bin;
+    }
+
+    /*
+     * SECURITY NOTE ON APPLYING CHECKSUMS TO SECRETS:
+     *
+     *      The checksum introduces a potential security weakness. For example,
+     *      suppose we apply a checksum to a key, and that an adversary has an
+     *      exploit against the process containing the key, such that they can
+     *      overwrite an arbitrary byte of memory and then cause the checksum to
+     *      be verified and learn the result.
+     *
+     *      In this scenario, the adversary can extract the key one byte at
+     *      a time by overwriting it with their guess of its value and then
+     *      asking if the checksum matches. If it does, their guess was right.
+     *      This kind of attack may be more easy to implement and more reliable
+     *      than a remote code execution attack.
+     *
+     *      This attack also applies to authenticated encryption as a whole, in
+     *      the situation where the adversary can overwrite a byte of the key
+     *      and then cause a valid ciphertext to be decrypted, and then
+     *      determine whether the MAC check passed or failed.
+     *
+     *      By using the full SHA256 hash instead of truncating it, I'm ensuring
+     *      that both ways of going about the attack are equivalently difficult.
+     *      A shorter checksum of say 32 bits might be more useful to the
+     *      adversary as an oracle in case their writes are coarser grained.
+     *
+     *      Because the scenario assumes a serious vulnerability, we don't try
+     *      to prevent attacks of this style.
+     */
+
+    /**
+     * INTERNAL USE ONLY: Applies a version header, applies a checksum, and
+     * then encodes a byte string into a range of printable ASCII characters.
+     *
+     * @param string $header
+     * @param string $bytes
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     *
+     * @return string
+     */
+    public static function saveBytesToChecksummedAsciiSafeString($header, $bytes)
+    {
+        // Headers must be a constant length to prevent one type's header from
+        // being a prefix of another type's header, leading to ambiguity.
+        if (Core::ourStrlen($header) !== self::SERIALIZE_HEADER_BYTES) {
+            throw new Ex\EnvironmentIsBrokenException(
+                'Header must be ' . self::SERIALIZE_HEADER_BYTES . ' bytes.'
+            );
+        }
+
+        return Encoding::binToHex(
+            $header .
+            $bytes .
+            \hash(
+                self::CHECKSUM_HASH_ALGO,
+                $header . $bytes,
+                true
+            )
+        );
+    }
+
+    /**
+     * INTERNAL USE ONLY: Decodes, verifies the header and checksum, and returns
+     * the encoded byte string.
+     *
+     * @param string $expected_header
+     * @param string $string
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     * @throws Ex\BadFormatException
+     *
+     * @return string
+     */
+    public static function loadBytesFromChecksummedAsciiSafeString($expected_header, $string)
+    {
+        // Headers must be a constant length to prevent one type's header from
+        // being a prefix of another type's header, leading to ambiguity.
+        if (Core::ourStrlen($expected_header) !== self::SERIALIZE_HEADER_BYTES) {
+            throw new Ex\EnvironmentIsBrokenException(
+                'Header must be 4 bytes.'
+            );
+        }
+
+        $bytes = Encoding::hexToBin($string);
+
+        /* Make sure we have enough bytes to get the version header and checksum. */
+        if (Core::ourStrlen($bytes) < self::SERIALIZE_HEADER_BYTES + self::CHECKSUM_BYTE_SIZE) {
+            throw new Ex\BadFormatException(
+                'Encoded data is shorter than expected.'
+            );
+        }
+
+        /* Grab the version header. */
+        $actual_header = Core::ourSubstr($bytes, 0, self::SERIALIZE_HEADER_BYTES);
+
+        if ($actual_header !== $expected_header) {
+            throw new Ex\BadFormatException(
+                'Invalid header.'
+            );
+        }
+
+        /* Grab the bytes that are part of the checksum. */
+        $checked_bytes = Core::ourSubstr(
+            $bytes,
+            0,
+            Core::ourStrlen($bytes) - self::CHECKSUM_BYTE_SIZE
+        );
+
+        /* Grab the included checksum. */
+        $checksum_a = Core::ourSubstr(
+            $bytes,
+            Core::ourStrlen($bytes) - self::CHECKSUM_BYTE_SIZE,
+            self::CHECKSUM_BYTE_SIZE
+        );
+
+        /* Re-compute the checksum. */
+        $checksum_b = \hash(self::CHECKSUM_HASH_ALGO, $checked_bytes, true);
+
+        /* Check if the checksum matches. */
+        if (! Core::hashEquals($checksum_a, $checksum_b)) {
+            throw new Ex\BadFormatException(
+                "Data is corrupted, the checksum doesn't match"
+            );
+        }
+
+        return Core::ourSubstr(
+            $bytes,
+            self::SERIALIZE_HEADER_BYTES,
+            Core::ourStrlen($bytes) - self::SERIALIZE_HEADER_BYTES - self::CHECKSUM_BYTE_SIZE
+        );
+    }
+}
diff --git a/includes/Defuse/Crypto/Exception/BadFormatException.php b/includes/Defuse/Crypto/Exception/BadFormatException.php
new file mode 100644
index 0000000..804d9c1
--- /dev/null
+++ b/includes/Defuse/Crypto/Exception/BadFormatException.php
@@ -0,0 +1,7 @@
+<?php
+
+namespace Defuse\Crypto\Exception;
+
+class BadFormatException extends \Defuse\Crypto\Exception\CryptoException
+{
+}
diff --git a/includes/Defuse/Crypto/Exception/CryptoException.php b/includes/Defuse/Crypto/Exception/CryptoException.php
new file mode 100644
index 0000000..8d6c57f
--- /dev/null
+++ b/includes/Defuse/Crypto/Exception/CryptoException.php
@@ -0,0 +1,7 @@
+<?php
+
+namespace Defuse\Crypto\Exception;
+
+class CryptoException extends \Exception
+{
+}
diff --git a/includes/Defuse/Crypto/Exception/EnvironmentIsBrokenException.php b/includes/Defuse/Crypto/Exception/EnvironmentIsBrokenException.php
new file mode 100644
index 0000000..7fbfc0a
--- /dev/null
+++ b/includes/Defuse/Crypto/Exception/EnvironmentIsBrokenException.php
@@ -0,0 +1,7 @@
+<?php
+
+namespace Defuse\Crypto\Exception;
+
+class EnvironmentIsBrokenException extends \Defuse\Crypto\Exception\CryptoException
+{
+}
diff --git a/includes/Defuse/Crypto/Exception/IOException.php b/includes/Defuse/Crypto/Exception/IOException.php
new file mode 100644
index 0000000..cda4d15
--- /dev/null
+++ b/includes/Defuse/Crypto/Exception/IOException.php
@@ -0,0 +1,7 @@
+<?php
+
+namespace Defuse\Crypto\Exception;
+
+class IOException extends \Defuse\Crypto\Exception\CryptoException
+{
+}
diff --git a/includes/Defuse/Crypto/Exception/WrongKeyOrModifiedCiphertextException.php b/includes/Defuse/Crypto/Exception/WrongKeyOrModifiedCiphertextException.php
new file mode 100644
index 0000000..4216861
--- /dev/null
+++ b/includes/Defuse/Crypto/Exception/WrongKeyOrModifiedCiphertextException.php
@@ -0,0 +1,7 @@
+<?php
+
+namespace Defuse\Crypto\Exception;
+
+class WrongKeyOrModifiedCiphertextException extends \Defuse\Crypto\Exception\CryptoException
+{
+}
diff --git a/includes/Defuse/Crypto/File.php b/includes/Defuse/Crypto/File.php
new file mode 100644
index 0000000..d739077
--- /dev/null
+++ b/includes/Defuse/Crypto/File.php
@@ -0,0 +1,755 @@
+<?php
+
+namespace Defuse\Crypto;
+
+use Defuse\Crypto\Exception as Ex;
+
+final class File
+{
+    /**
+     * Encrypts the input file, saving the ciphertext to the output file.
+     *
+     * @param string $inputFilename
+     * @param string $outputFilename
+     * @param Key    $key
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     * @throws Ex\IOException
+     */
+    public static function encryptFile($inputFilename, $outputFilename, Key $key)
+    {
+        self::encryptFileInternal(
+            $inputFilename,
+            $outputFilename,
+            KeyOrPassword::createFromKey($key)
+        );
+    }
+
+    /**
+     * Encrypts a file with a password, using a slow key derivation function to
+     * make password cracking more expensive.
+     *
+     * @param string $inputFilename
+     * @param string $outputFilename
+     * @param string $password
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     * @throws Ex\IOException
+     */
+    public static function encryptFileWithPassword($inputFilename, $outputFilename, $password)
+    {
+        self::encryptFileInternal(
+            $inputFilename,
+            $outputFilename,
+            KeyOrPassword::createFromPassword($password)
+        );
+    }
+
+    /**
+     * Decrypts the input file, saving the plaintext to the output file.
+     *
+     * @param string $inputFilename
+     * @param string $outputFilename
+     * @param Key    $key
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     * @throws Ex\IOException
+     * @throws Ex\WrongKeyOrModifiedCiphertextException
+     */
+    public static function decryptFile($inputFilename, $outputFilename, Key $key)
+    {
+        self::decryptFileInternal(
+            $inputFilename,
+            $outputFilename,
+            KeyOrPassword::createFromKey($key)
+        );
+    }
+
+    /**
+     * Decrypts a file with a password, using a slow key derivation function to
+     * make password cracking more expensive.
+     *
+     * @param string $inputFilename
+     * @param string $outputFilename
+     * @param string $password
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     * @throws Ex\IOException
+     * @throws Ex\WrongKeyOrModifiedCiphertextException
+     */
+    public static function decryptFileWithPassword($inputFilename, $outputFilename, $password)
+    {
+        self::decryptFileInternal(
+            $inputFilename,
+            $outputFilename,
+            KeyOrPassword::createFromPassword($password)
+        );
+    }
+
+    /**
+     * Takes two resource handles and encrypts the contents of the first,
+     * writing the ciphertext into the second.
+     *
+     * @param resource $inputHandle
+     * @param resource $outputHandle
+     * @param Key      $key
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     * @throws Ex\WrongKeyOrModifiedCiphertextException
+     */
+    public static function encryptResource($inputHandle, $outputHandle, Key $key)
+    {
+        self::encryptResourceInternal(
+            $inputHandle,
+            $outputHandle,
+            KeyOrPassword::createFromKey($key)
+        );
+    }
+
+    /**
+     * Encrypts the contents of one resource handle into another with a
+     * password, using a slow key derivation function to make password cracking
+     * more expensive.
+     *
+     * @param resource $inputHandle
+     * @param resource $outputHandle
+     * @param string   $password
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     * @throws Ex\IOException
+     * @throws Ex\WrongKeyOrModifiedCiphertextException
+     */
+    public static function encryptResourceWithPassword($inputHandle, $outputHandle, $password)
+    {
+        self::encryptResourceInternal(
+            $inputHandle,
+            $outputHandle,
+            KeyOrPassword::createFromPassword($password)
+        );
+    }
+
+    /**
+     * Takes two resource handles and decrypts the contents of the first,
+     * writing the plaintext into the second.
+     *
+     * @param resource $inputHandle
+     * @param resource $outputHandle
+     * @param Key      $key
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     * @throws Ex\IOException
+     * @throws Ex\WrongKeyOrModifiedCiphertextException
+     */
+    public static function decryptResource($inputHandle, $outputHandle, Key $key)
+    {
+        self::decryptResourceInternal(
+            $inputHandle,
+            $outputHandle,
+            KeyOrPassword::createFromKey($key)
+        );
+    }
+
+    /**
+     * Decrypts the contents of one resource into another with a password, using
+     * a slow key derivation function to make password cracking more expensive.
+     *
+     * @param resource $inputHandle
+     * @param resource $outputHandle
+     * @param string   $password
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     * @throws Ex\IOException
+     * @throws Ex\WrongKeyOrModifiedCiphertextException
+     */
+    public static function decryptResourceWithPassword($inputHandle, $outputHandle, $password)
+    {
+        self::decryptResourceInternal(
+            $inputHandle,
+            $outputHandle,
+            KeyOrPassword::createFromPassword($password)
+        );
+    }
+
+    /**
+     * Encrypts a file with either a key or a password.
+     *
+     * @param string        $inputFilename
+     * @param string        $outputFilename
+     * @param KeyOrPassword $secret
+     *
+     * @throws Ex\CryptoException
+     * @throws Ex\IOException
+     */
+    private static function encryptFileInternal($inputFilename, $outputFilename, KeyOrPassword $secret)
+    {
+        /* Open the input file. */
+        $if = @\fopen($inputFilename, 'rb');
+        if ($if === false) {
+            throw new Ex\IOException(
+                'Cannot open input file for encrypting: ' .
+                self::getLastErrorMessage()
+            );
+        }
+        if (\is_callable('\\stream_set_read_buffer')) {
+            /* This call can fail, but the only consequence is performance. */
+            \stream_set_read_buffer($if, 0);
+        }
+
+        /* Open the output file. */
+        $of = @\fopen($outputFilename, 'wb');
+        if ($of === false) {
+            \fclose($if);
+            throw new Ex\IOException(
+                'Cannot open output file for encrypting: ' .
+                self::getLastErrorMessage()
+            );
+        }
+        if (\is_callable('\\stream_set_write_buffer')) {
+            /* This call can fail, but the only consequence is performance. */
+            \stream_set_write_buffer($of, 0);
+        }
+
+        /* Perform the encryption. */
+        try {
+            self::encryptResourceInternal($if, $of, $secret);
+        } catch (Ex\CryptoException $ex) {
+            \fclose($if);
+            \fclose($of);
+            throw $ex;
+        }
+
+        /* Close the input file. */
+        if (\fclose($if) === false) {
+            \fclose($of);
+            throw new Ex\IOException(
+                'Cannot close input file after encrypting'
+            );
+        }
+
+        /* Close the output file. */
+        if (\fclose($of) === false) {
+            throw new Ex\IOException(
+                'Cannot close output file after encrypting'
+            );
+        }
+    }
+
+    /**
+     * Decrypts a file with either a key or a password.
+     *
+     * @param string        $inputFilename
+     * @param string        $outputFilename
+     * @param KeyOrPassword $secret
+     *
+     * @throws Ex\CryptoException
+     * @throws Ex\IOException
+     */
+    private static function decryptFileInternal($inputFilename, $outputFilename, KeyOrPassword $secret)
+    {
+        /* Open the input file. */
+        $if = @\fopen($inputFilename, 'rb');
+        if ($if === false) {
+            throw new Ex\IOException(
+                'Cannot open input file for decrypting: ' .
+                self::getLastErrorMessage()
+            );
+        }
+        
+        if (\is_callable('\\stream_set_read_buffer')) {
+            /* This call can fail, but the only consequence is performance. */
+            \stream_set_read_buffer($if, 0);
+        }
+
+        /* Open the output file. */
+        $of = @\fopen($outputFilename, 'wb');
+        if ($of === false) {
+            \fclose($if);
+            throw new Ex\IOException(
+                'Cannot open output file for decrypting: ' .
+                self::getLastErrorMessage()
+            );
+        }
+        
+        if (\is_callable('\\stream_set_write_buffer')) {
+            /* This call can fail, but the only consequence is performance. */
+            \stream_set_write_buffer($of, 0);
+        }
+
+        /* Perform the decryption. */
+        try {
+            self::decryptResourceInternal($if, $of, $secret);
+        } catch (Ex\CryptoException $ex) {
+            \fclose($if);
+            \fclose($of);
+            throw $ex;
+        }
+
+        /* Close the input file. */
+        if (\fclose($if) === false) {
+            \fclose($of);
+            throw new Ex\IOException(
+                'Cannot close input file after decrypting'
+            );
+        }
+
+        /* Close the output file. */
+        if (\fclose($of) === false) {
+            throw new Ex\IOException(
+                'Cannot close output file after decrypting'
+            );
+        }
+    }
+
+    /**
+     * Encrypts a resource with either a key or a password.
+     *
+     * @param resource      $inputHandle
+     * @param resource      $outputHandle
+     * @param KeyOrPassword $secret
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     * @throws Ex\IOException
+     */
+    private static function encryptResourceInternal($inputHandle, $outputHandle, KeyOrPassword $secret)
+    {
+        if (! \is_resource($inputHandle)) {
+            throw new Ex\IOException(
+                'Input handle must be a resource!'
+            );
+        }
+        if (! \is_resource($outputHandle)) {
+            throw new Ex\IOException(
+                'Output handle must be a resource!'
+            );
+        }
+
+        $inputStat = \fstat($inputHandle);
+        $inputSize = $inputStat['size'];
+
+        $file_salt = Core::secureRandom(Core::SALT_BYTE_SIZE);
+        $keys = $secret->deriveKeys($file_salt);
+        $ekey = $keys->getEncryptionKey();
+        $akey = $keys->getAuthenticationKey();
+
+        $ivsize = Core::BLOCK_BYTE_SIZE;
+        $iv     = Core::secureRandom($ivsize);
+
+        /* Initialize a streaming HMAC state. */
+        $hmac = \hash_init(Core::HASH_FUNCTION_NAME, HASH_HMAC, $akey);
+        if ($hmac === false) {
+            throw new Ex\EnvironmentIsBrokenException(
+                'Cannot initialize a hash context'
+            );
+        }
+
+        /* Write the header, salt, and IV. */
+        self::writeBytes(
+            $outputHandle,
+            Core::CURRENT_VERSION . $file_salt . $iv,
+            Core::HEADER_VERSION_SIZE + Core::SALT_BYTE_SIZE + $ivsize
+        );
+
+        /* Add the header, salt, and IV to the HMAC. */
+        \hash_update($hmac, Core::CURRENT_VERSION);
+        \hash_update($hmac, $file_salt);
+        \hash_update($hmac, $iv);
+
+        /* $thisIv will be incremented after each call to the encryption. */
+        $thisIv = $iv;
+
+        /* How many blocks do we encrypt at a time? We increment by this value. */
+        $inc = Core::BUFFER_BYTE_SIZE / Core::BLOCK_BYTE_SIZE;
+
+        /* Loop until we reach the end of the input file. */
+        $at_file_end = false;
+        while (! (\feof($inputHandle) || $at_file_end)) {
+            /* Find out if we can read a full buffer, or only a partial one. */
+            $pos = \ftell($inputHandle);
+            if ($pos === false) {
+                throw new Ex\IOException(
+                    'Could not get current position in input file during encryption'
+                );
+            }
+            if ($pos + Core::BUFFER_BYTE_SIZE >= $inputSize) {
+                /* We're at the end of the file, so we need to break out of the loop. */
+                $at_file_end = true;
+                $read = self::readBytes(
+                    $inputHandle,
+                    $inputSize - $pos
+                );
+            } else {
+                $read = self::readBytes(
+                    $inputHandle,
+                    Core::BUFFER_BYTE_SIZE
+                );
+            }
+
+            /* Encrypt this buffer. */
+            $encrypted = \openssl_encrypt(
+                $read,
+                Core::CIPHER_METHOD,
+                $ekey,
+                OPENSSL_RAW_DATA,
+                $thisIv
+            );
+
+            if ($encrypted === false) {
+                throw new Ex\EnvironmentIsBrokenException(
+                    'OpenSSL encryption error'
+                );
+            }
+
+            /* Write this buffer's ciphertext. */
+            self::writeBytes($outputHandle, $encrypted, Core::ourStrlen($encrypted));
+            /* Add this buffer's ciphertext to the HMAC. */
+            \hash_update($hmac, $encrypted);
+
+            /* Increment the counter by the number of blocks in a buffer. */
+            $thisIv = Core::incrementCounter($thisIv, $inc);
+            /* WARNING: Usually, unless the file is a multiple of the buffer
+             * size, $thisIv will contain an incorrect value here on the last
+             * iteration of this loop. */
+        }
+
+        /* Get the HMAC and append it to the ciphertext. */
+        $final_mac = \hash_final($hmac, true);
+        self::writeBytes($outputHandle, $final_mac, Core::MAC_BYTE_SIZE);
+    }
+
+    /**
+     * Decrypts a file-backed resource with either a key or a password.
+     *
+     * @param resource      $inputHandle
+     * @param resource      $outputHandle
+     * @param KeyOrPassword $secret
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     * @throws Ex\IOException
+     * @throws Ex\WrongKeyOrModifiedCiphertextException
+     */
+    public static function decryptResourceInternal($inputHandle, $outputHandle, KeyOrPassword $secret)
+    {
+        if (! \is_resource($inputHandle)) {
+            throw new Ex\IOException(
+                'Input handle must be a resource!'
+            );
+        }
+        if (! \is_resource($outputHandle)) {
+            throw new Ex\IOException(
+                'Output handle must be a resource!'
+            );
+        }
+
+        /* Make sure the file is big enough for all the reads we need to do. */
+        $stat = \fstat($inputHandle);
+        if ($stat['size'] < Core::MINIMUM_CIPHERTEXT_SIZE) {
+            throw new Ex\WrongKeyOrModifiedCiphertextException(
+                'Input file is too small to have been created by this library.'
+            );
+        }
+
+        /* Check the version header. */
+        $header = self::readBytes($inputHandle, Core::HEADER_VERSION_SIZE);
+        if ($header !== Core::CURRENT_VERSION) {
+            throw new Ex\WrongKeyOrModifiedCiphertextException(
+                'Bad version header.'
+            );
+        }
+
+        /* Get the salt. */
+        $file_salt = self::readBytes($inputHandle, Core::SALT_BYTE_SIZE);
+
+        /* Get the IV. */
+        $ivsize = Core::BLOCK_BYTE_SIZE;
+        $iv     = self::readBytes($inputHandle, $ivsize);
+
+        /* Derive the authentication and encryption keys. */
+        $keys = $secret->deriveKeys($file_salt);
+        $ekey = $keys->getEncryptionKey();
+        $akey = $keys->getAuthenticationKey();
+
+        /* We'll store the MAC of each buffer-sized chunk as we verify the
+         * actual MAC, so that we can check them again when decrypting. */
+        $macs = [];
+
+        /* $thisIv will be incremented after each call to the decryption. */
+        $thisIv = $iv;
+
+        /* How many blocks do we encrypt at a time? We increment by this value. */
+        $inc = Core::BUFFER_BYTE_SIZE / Core::BLOCK_BYTE_SIZE;
+
+        /* Get the HMAC. */
+        if (\fseek($inputHandle, (-1 * Core::MAC_BYTE_SIZE), SEEK_END) === false) {
+            throw new Ex\IOException(
+                'Cannot seek to beginning of MAC within input file'
+            );
+        }
+
+        /* Get the position of the last byte in the actual ciphertext. */
+        $cipher_end = \ftell($inputHandle);
+        if ($cipher_end === false) {
+            throw new Ex\IOException(
+                'Cannot read input file'
+            );
+        }
+        /* We have the position of the first byte of the HMAC. Go back by one. */
+        --$cipher_end;
+
+        /* Read the HMAC. */
+        $stored_mac = self::readBytes($inputHandle, Core::MAC_BYTE_SIZE);
+
+        /* Initialize a streaming HMAC state. */
+        $hmac = \hash_init(Core::HASH_FUNCTION_NAME, HASH_HMAC, $akey);
+        if ($hmac === false) {
+            throw new Ex\EnvironmentIsBrokenException(
+                'Cannot initialize a hash context'
+            );
+        }
+
+        /* Reset file pointer to the beginning of the file after the header */
+        if (\fseek($inputHandle, Core::HEADER_VERSION_SIZE, SEEK_SET) === false) {
+            throw new Ex\IOException(
+                'Cannot read seek within input file'
+            );
+        }
+
+        /* Seek to the start of the actual ciphertext. */
+        if (\fseek($inputHandle, Core::SALT_BYTE_SIZE + $ivsize, SEEK_CUR) === false) {
+            throw new Ex\IOException(
+                'Cannot seek input file to beginning of ciphertext'
+            );
+        }
+
+        /* PASS #1: Calculating the HMAC. */
+
+        \hash_update($hmac, $header);
+        \hash_update($hmac, $file_salt);
+        \hash_update($hmac, $iv);
+        $hmac2 = \hash_copy($hmac);
+
+        $break = false;
+        while (! $break) {
+            $pos = \ftell($inputHandle);
+            if ($pos === false) {
+                throw new Ex\IOException(
+                    'Could not get current position in input file during decryption'
+                );
+            }
+
+            /* Read the next buffer-sized chunk (or less). */
+            if ($pos + Core::BUFFER_BYTE_SIZE >= $cipher_end) {
+                $break = true;
+                $read  = self::readBytes(
+                    $inputHandle,
+                    $cipher_end - $pos + 1
+                );
+            } else {
+                $read = self::readBytes(
+                    $inputHandle,
+                    Core::BUFFER_BYTE_SIZE
+                );
+            }
+
+            /* Update the HMAC. */
+            \hash_update($hmac, $read);
+
+            /* Remember this buffer-sized chunk's HMAC. */
+            $chunk_mac = \hash_copy($hmac);
+            if ($chunk_mac === false) {
+                throw new Ex\EnvironmentIsBrokenException(
+                    'Cannot duplicate a hash context'
+                );
+            }
+            $macs []= \hash_final($chunk_mac);
+        }
+
+        /* Get the final HMAC, which should match the stored one. */
+        $final_mac = \hash_final($hmac, true);
+
+        /* Verify the HMAC. */
+        if (! Core::hashEquals($final_mac, $stored_mac)) {
+            throw new Ex\WrongKeyOrModifiedCiphertextException(
+                'Integrity check failed.'
+            );
+        }
+
+        /* PASS #2: Decrypt and write output. */
+
+        /* Rewind to the start of the actual ciphertext. */
+        if (\fseek($inputHandle, Core::SALT_BYTE_SIZE + $ivsize + Core::HEADER_VERSION_SIZE, SEEK_SET) === false) {
+            throw new Ex\IOException(
+                'Could not move the input file pointer during decryption'
+            );
+        }
+
+        $at_file_end = false;
+        while (! $at_file_end) {
+            $pos = \ftell($inputHandle);
+            if ($pos === false) {
+                throw new Ex\IOException(
+                    'Could not get current position in input file during decryption'
+                );
+            }
+
+            /* Read the next buffer-sized chunk (or less). */
+            if ($pos + Core::BUFFER_BYTE_SIZE >= $cipher_end) {
+                $at_file_end = true;
+                $read   = self::readBytes(
+                    $inputHandle,
+                    $cipher_end - $pos + 1
+                );
+            } else {
+                $read = self::readBytes(
+                    $inputHandle,
+                    Core::BUFFER_BYTE_SIZE
+                );
+            }
+
+            /* Recalculate the MAC (so far) and compare it with the one we
+             * remembered from pass #1 to ensure attackers didn't change the
+             * ciphertext after MAC verification. */
+            \hash_update($hmac2, $read);
+            $calc_mac = \hash_copy($hmac2);
+            if ($calc_mac === false) {
+                throw new Ex\EnvironmentIsBrokenException(
+                    'Cannot duplicate a hash context'
+                );
+            }
+            $calc = \hash_final($calc_mac);
+
+            if (empty($macs)) {
+                throw new Ex\WrongKeyOrModifiedCiphertextException(
+                    'File was modified after MAC verification'
+                );
+            } elseif (! Core::hashEquals(\array_shift($macs), $calc)) {
+                throw new Ex\WrongKeyOrModifiedCiphertextException(
+                    'File was modified after MAC verification'
+                );
+            }
+
+            /* Decrypt this buffer-sized chunk. */
+            $decrypted = \openssl_decrypt(
+                $read,
+                Core::CIPHER_METHOD,
+                $ekey,
+                OPENSSL_RAW_DATA,
+                $thisIv
+            );
+            if ($decrypted === false) {
+                throw new Ex\EnvironmentIsBrokenException(
+                    'OpenSSL decryption error'
+                );
+            }
+
+            /* Write the plaintext to the output file. */
+            self::writeBytes(
+                $outputHandle,
+                $decrypted,
+                Core::ourStrlen($decrypted)
+            );
+
+            /* Increment the IV by the amount of blocks in a buffer. */
+            $thisIv = Core::incrementCounter($thisIv, $inc);
+            /* WARNING: Usually, unless the file is a multiple of the buffer
+             * size, $thisIv will contain an incorrect value here on the last
+             * iteration of this loop. */
+        }
+    }
+
+    /**
+     * Read from a stream; prevent partial reads.
+     *
+     * @param resource $stream
+     * @param int      $num_bytes
+     *
+     * @throws Ex\IOException
+     * @throws Ex\EnvironmentIsBrokenException
+     *
+     * @return string
+     */
+    public static function readBytes($stream, $num_bytes)
+    {
+        if ($num_bytes < 0) {
+            throw new Ex\EnvironmentIsBrokenException(
+                'Tried to read less than 0 bytes'
+            );
+        } elseif ($num_bytes === 0) {
+            return '';
+        }
+        $buf       = '';
+        $remaining = $num_bytes;
+        while ($remaining > 0 && ! \feof($stream)) {
+            $read = \fread($stream, $remaining);
+
+            if ($read === false) {
+                throw new Ex\IOException(
+                    'Could not read from the file'
+                );
+            }
+            $buf .= $read;
+            $remaining -= Core::ourStrlen($read);
+        }
+        if (Core::ourStrlen($buf) !== $num_bytes) {
+            throw new Ex\IOException(
+                'Tried to read past the end of the file'
+            );
+        }
+        return $buf;
+    }
+
+    /**
+     * Write to a stream; prevents partial writes.
+     *
+     * @param resource $stream
+     * @param string   $buf
+     * @param int      $num_bytes
+     *
+     * @throws Ex\IOException
+     *
+     * @return string
+     */
+    public static function writeBytes($stream, $buf, $num_bytes = null)
+    {
+        $bufSize = Core::ourStrlen($buf);
+        if ($num_bytes === null) {
+            $num_bytes = $bufSize;
+        }
+        if ($num_bytes > $bufSize) {
+            throw new Ex\IOException(
+                'Trying to write more bytes than the buffer contains.'
+            );
+        }
+        if ($num_bytes < 0) {
+            throw new Ex\IOException(
+                'Tried to write less than 0 bytes'
+            );
+        }
+        $remaining = $num_bytes;
+        while ($remaining > 0) {
+            $written = \fwrite($stream, $buf, $remaining);
+            if ($written === false) {
+                throw new Ex\IOException(
+                    'Could not write to the file'
+                );
+            }
+            $buf = Core::ourSubstr($buf, $written, null);
+            $remaining -= $written;
+        }
+        return $num_bytes;
+    }
+
+    /**
+     * Returns the last PHP error's or warning's message string.
+     *
+     * @return string
+     */
+    private static function getLastErrorMessage()
+    {
+        $error = error_get_last();
+        if ($error === null) {
+            return '[no PHP error]';
+        } else {
+            return $error['message'];
+        }
+    }
+}
diff --git a/includes/Defuse/Crypto/Key.php b/includes/Defuse/Crypto/Key.php
new file mode 100644
index 0000000..ca7b9b2
--- /dev/null
+++ b/includes/Defuse/Crypto/Key.php
@@ -0,0 +1,84 @@
+<?php
+
+namespace Defuse\Crypto;
+
+use Defuse\Crypto\Exception as Ex;
+
+final class Key
+{
+    const KEY_CURRENT_VERSION = "\xDE\xF0\x00\x00";
+    const KEY_BYTE_SIZE       = 32;
+
+    private $key_bytes = null;
+
+    /**
+     * Creates new random key.
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     *
+     * @return Key
+     */
+    public static function createNewRandomKey()
+    {
+        return new Key(Core::secureRandom(self::KEY_BYTE_SIZE));
+    }
+
+    /**
+     * Loads a Key from its encoded form.
+     *
+     * @param string $saved_key_string
+     *
+     * @throws Ex\BadFormatException
+     * @throws Ex\EnvironmentIsBrokenException
+     *
+     * @return Key
+     */
+    public static function loadFromAsciiSafeString($saved_key_string)
+    {
+        $key_bytes = Encoding::loadBytesFromChecksummedAsciiSafeString(self::KEY_CURRENT_VERSION, $saved_key_string);
+        return new Key($key_bytes);
+    }
+
+    /**
+     * Encodes the Key into a string of printable ASCII characters.
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     *
+     * @return string
+     */
+    public function saveToAsciiSafeString()
+    {
+        return Encoding::saveBytesToChecksummedAsciiSafeString(
+            self::KEY_CURRENT_VERSION,
+            $this->key_bytes
+        );
+    }
+
+    /**
+     * Gets the raw bytes of the key.
+     *
+     * @return string
+     */
+    public function getRawBytes()
+    {
+        return $this->key_bytes;
+    }
+
+    /**
+     * Constructs a new Key object from a string of raw bytes.
+     *
+     * @param string $bytes
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     */
+    private function __construct($bytes)
+    {
+        if (Core::ourStrlen($bytes) !== self::KEY_BYTE_SIZE) {
+            throw new Ex\EnvironmentIsBrokenException(
+                'Bad key length.'
+            );
+        }
+        $this->key_bytes = $bytes;
+    }
+
+}
diff --git a/includes/Defuse/Crypto/KeyOrPassword.php b/includes/Defuse/Crypto/KeyOrPassword.php
new file mode 100644
index 0000000..2a46b71
--- /dev/null
+++ b/includes/Defuse/Crypto/KeyOrPassword.php
@@ -0,0 +1,119 @@
+<?php
+
+namespace Defuse\Crypto;
+
+use Defuse\Crypto\Exception as Ex;
+
+final class KeyOrPassword
+{
+    const PBKDF2_ITERATIONS    = 100000;
+    const SECRET_TYPE_KEY      = 1;
+    const SECRET_TYPE_PASSWORD = 2;
+
+    private $secret_type = null;
+    private $secret      = null;
+
+    /**
+     * Initializes an instance of KeyOrPassword from a key.
+     *
+     * @param Key $key
+     *
+     * @return KeyOrPassword
+     */
+    public static function createFromKey(Key $key)
+    {
+        return new KeyOrPassword(self::SECRET_TYPE_KEY, $key);
+    }
+
+    /**
+     * Initializes an instance of KeyOrPassword from a password.
+     *
+     * @param string $password
+     *
+     * @return KeyOrPassword
+     */
+    public static function createFromPassword($password)
+    {
+        return new KeyOrPassword(self::SECRET_TYPE_PASSWORD, $password);
+    }
+
+    /**
+     * Derives authentication and encryption keys from the secret, using a slow
+     * key derivation function if the secret is a password.
+     *
+     * @param string $salt
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     *
+     * @return DerivedKeys
+     */
+    public function deriveKeys($salt)
+    {
+        if (Core::ourStrlen($salt) !== Core::SALT_BYTE_SIZE) {
+            throw new Ex\EnvironmentIsBrokenException('Bad salt.');
+        }
+
+        if ($this->secret_type === self::SECRET_TYPE_KEY) {
+            $akey = Core::HKDF(
+                Core::HASH_FUNCTION_NAME,
+                $this->secret->getRawBytes(),
+                Core::KEY_BYTE_SIZE,
+                Core::AUTHENTICATION_INFO_STRING,
+                $salt
+            );
+            $ekey = Core::HKDF(
+                Core::HASH_FUNCTION_NAME,
+                $this->secret->getRawBytes(),
+                Core::KEY_BYTE_SIZE,
+                Core::ENCRYPTION_INFO_STRING,
+                $salt
+            );
+            return new DerivedKeys($akey, $ekey);
+        } elseif ($this->secret_type === self::SECRET_TYPE_PASSWORD) {
+            /* Our PBKDF2 polyfill is vulnerable to a DoS attack documented in
+             * GitHub issue #230. The fix is to pre-hash the password to ensure
+             * it is short. We do the prehashing here instead of in pbkdf2() so
+             * that pbkdf2() still computes the function as defined by the
+             * standard. */
+            $prehash = \hash(Core::HASH_FUNCTION_NAME, $this->secret, true);
+            $prekey = Core::pbkdf2(
+                Core::HASH_FUNCTION_NAME,
+                $prehash,
+                $salt,
+                self::PBKDF2_ITERATIONS,
+                Core::KEY_BYTE_SIZE,
+                true
+            );
+            $akey = Core::HKDF(
+                Core::HASH_FUNCTION_NAME,
+                $prekey,
+                Core::KEY_BYTE_SIZE,
+                Core::AUTHENTICATION_INFO_STRING,
+                $salt
+            );
+            /* Note the cryptographic re-use of $salt here. */
+            $ekey = Core::HKDF(
+                Core::HASH_FUNCTION_NAME,
+                $prekey,
+                Core::KEY_BYTE_SIZE,
+                Core::ENCRYPTION_INFO_STRING,
+                $salt
+            );
+            return new DerivedKeys($akey, $ekey);
+        } else {
+            throw new Ex\EnvironmentIsBrokenException('Bad secret type.');
+        }
+    }
+
+    /**
+     * Constructor for KeyOrPassword.
+     *
+     * @param int   $secret_type
+     * @param mixed $secret      (either a Key or a password string)
+     */
+    private function __construct($secret_type, $secret)
+    {
+        $this->secret_type = $secret_type;
+        $this->secret = $secret;
+    }
+}
diff --git a/includes/Defuse/Crypto/KeyProtectedByPassword.php b/includes/Defuse/Crypto/KeyProtectedByPassword.php
new file mode 100644
index 0000000..b9a40f1
--- /dev/null
+++ b/includes/Defuse/Crypto/KeyProtectedByPassword.php
@@ -0,0 +1,112 @@
+<?php
+
+namespace Defuse\Crypto;
+
+use Defuse\Crypto\Exception as Ex;
+
+final class KeyProtectedByPassword
+{
+    const PASSWORD_KEY_CURRENT_VERSION = "\xDE\xF1\x00\x00";
+
+    private $encrypted_key = null;
+
+    /**
+     * Creates a random key protected by the provided password.
+     *
+     * @param string $password
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     *
+     * @return KeyProtectedByPassword
+     */
+    public static function createRandomPasswordProtectedKey($password)
+    {
+        $inner_key = Key::createNewRandomKey();
+        /* The password is hashed as a form of poor-man's domain separation
+         * between this use of encryptWithPassword() and other uses of
+         * encryptWithPassword() that the user may also be using as part of the
+         * same protocol. */
+        $encrypted_key = Crypto::encryptWithPassword(
+            $inner_key->saveToAsciiSafeString(),
+            \hash(Core::HASH_FUNCTION_NAME, $password, true),
+            true
+        );
+
+        return new KeyProtectedByPassword($encrypted_key);
+    }
+
+    /**
+     * Loads a KeyProtectedByPassword from its encoded form.
+     *
+     * @param string $saved_key_string
+     *
+     * @throws Ex\BadFormatException
+     *
+     * @return KeyProtectedByPassword
+     */
+    public static function loadFromAsciiSafeString($saved_key_string)
+    {
+        $encrypted_key = Encoding::loadBytesFromChecksummedAsciiSafeString(
+            self::PASSWORD_KEY_CURRENT_VERSION,
+            $saved_key_string
+        );
+        return new KeyProtectedByPassword($encrypted_key);
+    }
+
+    /**
+     * Encodes the KeyProtectedByPassword into a string of printable ASCII
+     * characters.
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     *
+     * @return string
+     */
+    public function saveToAsciiSafeString()
+    {
+        return Encoding::saveBytesToChecksummedAsciiSafeString(
+            self::PASSWORD_KEY_CURRENT_VERSION,
+            $this->encrypted_key
+        );
+    }
+
+    /**
+     * Decrypts the protected key, returning an unprotected Key object that can
+     * be used for encryption and decryption.
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     * @throws Ex\WrongKeyOrModifiedCiphertextException
+     *
+     * @return Key
+     */
+    public function unlockKey($password)
+    {
+        try {
+            $inner_key_encoded = Crypto::decryptWithPassword(
+                $this->encrypted_key,
+                \hash(Core::HASH_FUNCTION_NAME, $password, true),
+                true
+            );
+            return Key::loadFromAsciiSafeString($inner_key_encoded);
+        } catch (Ex\BadFormatException $ex) {
+            /* This should never happen unless an attacker replaced the
+             * encrypted key ciphertext with some other ciphertext that was
+             * encrypted with the same password. We transform the exception type
+             * here in order to make the API simpler, avoiding the need to
+             * document that this method might throw an Ex\BadFormatException. */
+            throw new Ex\WrongKeyOrModifiedCiphertextException(
+                "The decrypted key was found to be in an invalid format. " .
+                "This very likely indicates it was modified by an attacker."
+            );
+        }
+    }
+
+    /**
+     * Constructor for KeyProtectedByPassword.
+     *
+     * @param string $encrypted_key
+     */
+    private function __construct($encrypted_key)
+    {
+        $this->encrypted_key = $encrypted_key;
+    }
+}
diff --git a/includes/Defuse/Crypto/RuntimeTests.php b/includes/Defuse/Crypto/RuntimeTests.php
new file mode 100644
index 0000000..9c0ba33
--- /dev/null
+++ b/includes/Defuse/Crypto/RuntimeTests.php
@@ -0,0 +1,242 @@
+<?php
+
+namespace Defuse\Crypto;
+
+use Defuse\Crypto\Exception as Ex;
+
+/*
+ * We're using static class inheritance to get access to protected methods
+ * inside Crypto. To make it easy to know where the method we're calling can be
+ * found, within this file, prefix calls with `Crypto::` or `RuntimeTests::`,
+ * and don't use `self::`.
+ */
+
+class RuntimeTests extends Crypto
+{
+    /**
+     * Runs the runtime tests.
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     */
+    public static function runtimeTest()
+    {
+        // 0: Tests haven't been run yet.
+        // 1: Tests have passed.
+        // 2: Tests are running right now.
+        // 3: Tests have failed.
+        static $test_state = 0;
+
+        if ($test_state === 1 || $test_state === 2) {
+            return;
+        }
+
+        if ($test_state === 3) {
+            /* If an intermittent problem caused a test to fail previously, we
+             * want that to be indicated to the user with every call to this
+             * library. This way, if the user first does something they really
+             * don't care about, and just ignores all exceptions, they won't get
+             * screwed when they then start to use the library for something
+             * they do care about. */
+            throw new Ex\EnvironmentIsBrokenException('Tests failed previously.');
+        }
+
+        try {
+            $test_state = 2;
+
+            Core::ensureFunctionExists('openssl_get_cipher_methods');
+            if (\in_array(Core::CIPHER_METHOD, \openssl_get_cipher_methods()) === false) {
+                throw new Ex\EnvironmentIsBrokenException(
+                    'Cipher method not supported. This is normally caused by an outdated ' .
+                    'version of OpenSSL (and/or OpenSSL compiled for FIPS compliance). ' .
+                    'Please upgrade to a newer version of OpenSSL that supports ' .
+                    Core::CIPHER_METHOD . ' to use this library.'
+                );
+            }
+
+            RuntimeTests::AESTestVector();
+            RuntimeTests::HMACTestVector();
+            RuntimeTests::HKDFTestVector();
+
+            RuntimeTests::testEncryptDecrypt();
+            if (Core::ourStrlen(Key::createNewRandomKey()->getRawBytes()) != Core::KEY_BYTE_SIZE) {
+                throw new Ex\EnvironmentIsBrokenException();
+            }
+
+            if (Core::ENCRYPTION_INFO_STRING == Core::AUTHENTICATION_INFO_STRING) {
+                throw new Ex\EnvironmentIsBrokenException();
+            }
+        } catch (Ex\EnvironmentIsBrokenException $ex) {
+            // Do this, otherwise it will stay in the "tests are running" state.
+            $test_state = 3;
+            throw $ex;
+        }
+
+        // Change this to '0' make the tests always re-run (for benchmarking).
+        $test_state = 1;
+    }
+
+    /**
+     * High-level tests of Crypto operations.
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     */
+    private static function testEncryptDecrypt()
+    {
+        $key  = Key::createNewRandomKey();
+        $data = "EnCrYpT EvErYThInG\x00\x00";
+
+        // Make sure encrypting then decrypting doesn't change the message.
+        $ciphertext = Crypto::encrypt($data, $key, true);
+        try {
+            $decrypted = Crypto::decrypt($ciphertext, $key, true);
+        } catch (Ex\WrongKeyOrModifiedCiphertextException $ex) {
+            // It's important to catch this and change it into a
+            // Ex\EnvironmentIsBrokenException, otherwise a test failure could trick
+            // the user into thinking it's just an invalid ciphertext!
+            throw new Ex\EnvironmentIsBrokenException();
+        }
+        if ($decrypted !== $data) {
+            throw new Ex\EnvironmentIsBrokenException();
+        }
+
+        // Modifying the ciphertext: Appending a string.
+        try {
+            Crypto::decrypt($ciphertext . 'a', $key, true);
+            throw new Ex\EnvironmentIsBrokenException();
+        } catch (Ex\WrongKeyOrModifiedCiphertextException $e) { /* expected */
+        }
+
+        // Modifying the ciphertext: Changing an HMAC byte.
+        $indices_to_change = [
+            0, // The header.
+            Core::HEADER_VERSION_SIZE + 1, // the salt
+            Core::HEADER_VERSION_SIZE + Core::SALT_BYTE_SIZE + 1, // the IV
+            Core::HEADER_VERSION_SIZE + Core::SALT_BYTE_SIZE + Core::BLOCK_BYTE_SIZE + 1, // the ciphertext
+        ];
+
+        foreach ($indices_to_change as $index) {
+            try {
+                $ciphertext[$index] = \chr((\ord($ciphertext[$index]) + 1) % 256);
+                Crypto::decrypt($ciphertext, $key, true);
+                throw new Ex\EnvironmentIsBrokenException();
+            } catch (Ex\WrongKeyOrModifiedCiphertextException $e) { /* expected */
+            }
+        }
+
+        // Decrypting with the wrong key.
+        $key        = Key::createNewRandomKey();
+        $data       = 'abcdef';
+        $ciphertext = Crypto::encrypt($data, $key, true);
+        $wrong_key  = Key::createNewRandomKey();
+        try {
+            Crypto::decrypt($ciphertext, $wrong_key, true);
+            throw new Ex\EnvironmentIsBrokenException();
+        } catch (Ex\WrongKeyOrModifiedCiphertextException $e) { /* expected */
+        }
+
+        // Ciphertext too small.
+        $key        = Key::createNewRandomKey();
+        $ciphertext = \str_repeat('A', Core::MINIMUM_CIPHERTEXT_SIZE - 1);
+        try {
+            Crypto::decrypt($ciphertext, $key, true);
+            throw new Ex\EnvironmentIsBrokenException();
+        } catch (Ex\WrongKeyOrModifiedCiphertextException $e) { /* expected */
+        }
+    }
+
+    /**
+     * Test HKDF against test vectors.
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     */
+    private static function HKDFTestVector()
+    {
+        // HKDF test vectors from RFC 5869
+
+        // Test Case 1
+        $ikm    = \str_repeat("\x0b", 22);
+        $salt   = Encoding::hexToBin('000102030405060708090a0b0c');
+        $info   = Encoding::hexToBin('f0f1f2f3f4f5f6f7f8f9');
+        $length = 42;
+        $okm    = Encoding::hexToBin(
+            '3cb25f25faacd57a90434f64d0362f2a' .
+            '2d2d0a90cf1a5a4c5db02d56ecc4c5bf' .
+            '34007208d5b887185865'
+        );
+        $computed_okm = Core::HKDF('sha256', $ikm, $length, $info, $salt);
+        if ($computed_okm !== $okm) {
+            throw new Ex\EnvironmentIsBrokenException();
+        }
+
+        // Test Case 7
+        $ikm    = \str_repeat("\x0c", 22);
+        $length = 42;
+        $okm    = Encoding::hexToBin(
+            '2c91117204d745f3500d636a62f64f0a' .
+            'b3bae548aa53d423b0d1f27ebba6f5e5' .
+            '673a081d70cce7acfc48'
+        );
+        $computed_okm = Core::HKDF('sha1', $ikm, $length, '', null);
+        if ($computed_okm !== $okm) {
+            throw new Ex\EnvironmentIsBrokenException();
+        }
+    }
+
+    /**
+     * Test HMAC against test vectors.
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     */
+    private static function HMACTestVector()
+    {
+        // HMAC test vector From RFC 4231 (Test Case 1)
+        $key     = \str_repeat("\x0b", 20);
+        $data    = 'Hi There';
+        $correct = 'b0344c61d8db38535ca8afceaf0bf12b881dc200c9833da726e9376c2e32cff7';
+        if (\hash_hmac(Core::HASH_FUNCTION_NAME, $data, $key) !== $correct) {
+            throw new Ex\EnvironmentIsBrokenException();
+        }
+    }
+
+    /**
+     * Test AES against test vectors.
+     *
+     * @throws Ex\EnvironmentIsBrokenException
+     */
+    private static function AESTestVector()
+    {
+        // AES CTR mode test vector from NIST SP 800-38A
+        $key = Encoding::hexToBin(
+            '603deb1015ca71be2b73aef0857d7781' .
+            '1f352c073b6108d72d9810a30914dff4'
+        );
+        $iv        = Encoding::hexToBin('f0f1f2f3f4f5f6f7f8f9fafbfcfdfeff');
+        $plaintext = Encoding::hexToBin(
+            '6bc1bee22e409f96e93d7e117393172a' .
+            'ae2d8a571e03ac9c9eb76fac45af8e51' .
+            '30c81c46a35ce411e5fbc1191a0a52ef' .
+            'f69f2445df4f9b17ad2b417be66c3710'
+        );
+        $ciphertext = Encoding::hexToBin(
+            '601ec313775789a5b7a7f504bbf3d228' .
+            'f443e3ca4d62b59aca84e990cacaf5c5' .
+            '2b0930daa23de94ce87017ba2d84988d' .
+            'dfc9c58db67aada613c2dd08457941a6'
+        );
+
+        $computed_ciphertext = Crypto::plainEncrypt($plaintext, $key, $iv);
+        if ($computed_ciphertext !== $ciphertext) {
+            echo \str_repeat("\n", 30);
+            echo \bin2hex($computed_ciphertext);
+            echo "\n---\n";
+            echo \bin2hex($ciphertext);
+            echo \str_repeat("\n", 30);
+            throw new Ex\EnvironmentIsBrokenException();
+        }
+
+        $computed_plaintext = Crypto::plainDecrypt($ciphertext, $key, $iv, Core::CIPHER_METHOD);
+        if ($computed_plaintext !== $plaintext) {
+            throw new Ex\EnvironmentIsBrokenException();
+        }
+    }
+}
diff --git a/includes/openid-connect-generic-client-wrapper.php b/includes/openid-connect-generic-client-wrapper.php
index 3e7890b..06dd1fc 100644
--- a/includes/openid-connect-generic-client-wrapper.php
+++ b/includes/openid-connect-generic-client-wrapper.php
@@ -10,8 +10,8 @@ class OpenID_Connect_Generic_Client_Wrapper {
 	// logger object
 	private $logger;
 
-	// internal tracking cookie key
-	private $cookie_id_key = 'openid-connect-generic-identity';
+	// token refresh info cookie key
+	private $cookie_token_refresh_key = 'openid-connect-generic-refresh';
 
 	// user redirect cookie key
 	public $cookie_redirect_key = 'openid-connect-generic-redirect';
@@ -47,8 +47,6 @@ class OpenID_Connect_Generic_Client_Wrapper {
 		// remove cookies on logout
 		add_action( 'wp_logout', array( $client_wrapper, 'wp_logout' ) );
 
-		// verify legitimacy of user token on admin pages
-		add_action( 'admin_init', array( $client_wrapper, 'check_user_token' ) );
 
 		// alter the requests according to settings
 		add_filter( 'openid-connect-generic-alter-request', array( $client_wrapper, 'alter_request' ), 10, 3 );
@@ -63,7 +61,7 @@ class OpenID_Connect_Generic_Client_Wrapper {
 		
 		// verify token for any logged in user
 		if ( is_user_logged_in() ) {
-			$client_wrapper->check_user_token();
+			$client_wrapper->ensure_tokens_still_fresh();
 		}
 		
 		return $client_wrapper;
@@ -93,16 +91,47 @@ class OpenID_Connect_Generic_Client_Wrapper {
 		return $this->client->make_authentication_url();
 	}
 
-	/**
-	 * Check the user's cookie
-	 */
-	function check_user_token() {
+	function ensure_tokens_still_fresh() {
+		if ( ! is_user_logged_in() ) {
+			return;
+		}
+
 		$is_openid_connect_user = get_user_meta( wp_get_current_user()->ID, 'openid-connect-generic-user', TRUE );
+		if ( empty( $is_openid_connect_user ) ) {
+			return;
+		}
+
+		if ( ! isset( $_COOKIE[ $this->cookie_token_refresh_key] ) ) {
+			wp_logout();
+			$this->error_redirect( new WP_Error( 'token-refresh-cookie-missing', __( 'Single sign-on cookie missing. Please login again.' ), $_COOKIE ) );
+			exit;
+		}
+
+		$user_id = wp_get_current_user()->ID;
+		$current_time = current_time( 'timestamp', TRUE );
+		$refresh_token_info = $this->read_token_refresh_info_from_cookie( $user_id );
 
-		if ( is_user_logged_in() && ! empty( $is_openid_connect_user ) && ! isset( $_COOKIE[ $this->cookie_id_key ] ) ) {
+		if ( ! $refresh_token_info ) {
 			wp_logout();
-			$this->error_redirect( new WP_Error( 'mismatch-identity', __( 'Mismatch identity' ), $_COOKIE ) );
+			$this->error_redirect( new WP_Error( 'token-refresh-cookie-missing', __( 'Single sign-on cookie invalid. Please login again.' ), $_COOKIE ) );
 		}
+
+		$next_access_token_refresh_time = $refresh_token_info[ 'next_access_token_refresh_time' ];
+		$refresh_token = $refresh_token_info[ 'refresh_token' ];
+
+		if ( $current_time < $next_access_token_refresh_time ) {
+			return;
+		}
+
+		$token_result = $this->client->request_new_tokens( $refresh_token );
+		$token_response = $this->client->get_token_response( $token_result );
+
+		if ( is_wp_error( $token_response ) ) {
+			wp_logout();
+			$this->error_redirect( $token_response );
+		}
+
+		$this->issue_token_refresh_info_cookie( $user_id, $token_response );
 	}
 
 	/**
@@ -144,7 +173,7 @@ class OpenID_Connect_Generic_Client_Wrapper {
 				update_user_meta( wp_get_current_user()->ID, 'openid-connect-generic-user', FALSE );
 		}
 		
-		setcookie( $this->cookie_id_key, false, 0, COOKIEPATH, COOKIE_DOMAIN, is_ssl() );
+		setcookie( $this->cookie_token_refresh_key, false, 1, COOKIEPATH, COOKIE_DOMAIN, is_ssl() );
 	}
 
 	/**
@@ -314,14 +343,59 @@ class OpenID_Connect_Generic_Client_Wrapper {
 		if( $this->settings->link_existing_users ) {
 			update_user_meta( $user->ID, 'openid-connect-generic-user', TRUE );
 		}
-		
-		// save our authorization cookie for the response expiration
-		$oauth_expiry = $token_response['expires_in'] + current_time( 'timestamp', TRUE );
-		setcookie( $this->cookie_id_key, $subject_identity, $oauth_expiry, COOKIEPATH, COOKIE_DOMAIN, is_ssl() );
 
 		// you did great, have a cookie!
+		$this->issue_token_refresh_info_cookie( $user->ID, $token_response );
 		wp_set_auth_cookie( $user->ID, FALSE );
 	}
+
+	function issue_token_refresh_info_cookie( $user_id, $token_response ) {
+		$cookie_value = serialize( array(
+			'next_access_token_refresh_time' =>  $token_response['expires_in'] + current_time( 'timestamp' , TRUE ),
+			'refresh_token' => $token_response[ 'refresh_token' ]
+		) );
+		$key = $this->get_refresh_cookie_encryption_key( $user_id );
+		$encrypted_cookie_value = \Defuse\Crypto\Crypto::encrypt( $cookie_value, $key );
+		setcookie( $this->cookie_token_refresh_key, $encrypted_cookie_value, 0, COOKIEPATH, COOKIE_DOMAIN, is_ssl() );
+	}
+
+	function read_token_refresh_info_from_cookie( $user_id ) {
+		if ( ! isset( $_COOKIE[ $this->cookie_token_refresh_key ] ) ) {
+			return false;
+		}
+
+		try {
+			$encrypted_cookie_value = $_COOKIE[$this->cookie_token_refresh_key];
+			$key = $this->get_refresh_cookie_encryption_key( $user_id );
+			$cookie_value = unserialize( \Defuse\Crypto\Crypto::decrypt($encrypted_cookie_value, $key) );
+
+			if ( ! isset( $cookie_value[ 'next_access_token_refresh_time' ] ) || ! $cookie_value[ 'next_access_token_refresh_time' ]
+				|| ! isset( $cookie_value[ 'refresh_token' ] ) || ! $cookie_value[ 'refresh_token' ] ) {
+				return false;
+			}
+
+			return $cookie_value;
+		}
+		catch ( Exception $e ) {
+			$this->logger->log( $e->getMessage() );
+			return false;
+		}
+	}
+
+	function get_refresh_cookie_encryption_key( $user_id ) {
+		$meta_key = 'openid-connect-generic-refresh-cookie-key';
+		$existing_key_string = get_user_meta( $user_id, $meta_key, true );
+
+		try {
+			$user_encryption_key = \Defuse\Crypto\Key::loadFromAsciiSafeString( $existing_key_string );
+		} catch ( Exception $e ) {
+			$this->logger->log( "Error loading user {$user_id} refresh token cookie key, generating new: " . $e->getMessage() );
+			$user_encryption_key = \Defuse\Crypto\Key::createNewRandomKey();
+			update_user_meta( $user_id, $meta_key, $user_encryption_key->saveToAsciiSafeString() );
+		}
+
+		return $user_encryption_key;
+	}
 	
 	/**
 	 * Get the user that has meta data matching a 
diff --git a/includes/openid-connect-generic-client.php b/includes/openid-connect-generic-client.php
index 4561c89..65d2ebc 100644
--- a/includes/openid-connect-generic-client.php
+++ b/includes/openid-connect-generic-client.php
@@ -118,6 +118,35 @@ class OpenID_Connect_Generic_Client {
 		return $response;
 	}
 
+	/**
+	 * Using the refresh token, request new tokens from the idp
+	 *
+	 * @param $refresh_token - refresh token previously obtained from token response.
+	 *
+	 * @return array|\WP_Error
+	 */
+	function request_new_tokens( $refresh_token ) {
+		$request = array(
+			'body' => array(
+				'refresh_token' => $refresh_token,
+				'client_id'     => $this->client_id,
+				'client_secret' => $this->client_secret,
+				'grant_type'    => 'refresh_token'
+			)
+		);
+
+		// allow modifications to the request
+		$request = apply_filters( 'openid-connect-generic-alter-request', $request, 'refresh-token' );
+
+		// call the server and ask for new tokens
+		$response = wp_remote_post( $this->endpoint_token, $request );
+
+		if ( is_wp_error( $response ) ) {
+			$response->add( 'refresh_token' , __( 'Refresh token failed.' ) );
+		}
+
+		return $response;
+	}
 
 	/**
 	 * Extract and decode the token body of a token response
@@ -133,6 +162,15 @@ class OpenID_Connect_Generic_Client {
 		// extract token response from token
 		$token_response = json_decode( $token_result['body'], TRUE );
 
+		if ( isset( $token_response[ 'error' ] ) ) {
+			$error = $token_response[ 'error' ];
+			$error_description = $error;
+			if ( isset( $token_response[ 'error_description' ] ) ) {
+				$error_description = $token_response[ 'error_description' ];
+			}
+			return new WP_Error( $error, $error_description, $token_result );
+		}
+
 		return $token_response;
 	}
 
diff --git a/openid-connect-generic.php b/openid-connect-generic.php
index 021b230..39c060e 100644
--- a/openid-connect-generic.php
+++ b/openid-connect-generic.php
@@ -28,7 +28,8 @@ Notes
   - openid-connect-generic-user                - (bool) if the user was created by this plugin
   - openid-connect-generic-subject-identity    - the identity of the user provided by the idp
   - openid-connect-generic-last-id-token-claim - the user's most recent id_token claim, decoded
-  - openid-connect-generic-last-user-claim     - the user's most recent user_claim 
+  - openid-connect-generic-last-user-claim     - the user's most recent user_claim
+  - openid-connect-generic-refresh-cookie-key  - encryption key used to secure refresh token info in cookie
   
   Options
   - openid_connect_generic_settings     - plugin settings
@@ -149,7 +150,11 @@ class OpenID_Connect_Generic {
 	 * @param $class
 	 */
 	static public function autoload( $class ) {
-		$filename = strtolower( str_replace( '_', '-', $class ) ) . '.php';
+		$filename = $class . '.php';
+		if ( false === strpos( $class, '\\' ) ) {
+			$filename = strtolower( str_replace( '_', '-', $class ) ) . '.php';
+		}
+
 		$filepath = dirname( __FILE__ ) . '/includes/' . $filename;
 		
 		if ( file_exists( $filepath ) ) {