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<?php
/*
* PHP Encryption Library
* Copyright (c) 2014, Taylor Hornby
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
/*
* Web: https://defuse.ca/secure-php-encryption.htm
* GitHub: https://github.com/defuse/php-encryption
*
* WARNING: This encryption library is not a silver bullet. It only provides
* symmetric encryption given a uniformly random key. This means you MUST NOT
* use an ASCII string like a password as the key parameter, it MUST be
* a uniformly random key generated by CreateNewRandomKey(). If you want to
* encrypt something with a password, apply a password key derivation function
* like PBKDF2 or scrypt with a random salt to generate a key.
*
* WARNING: Error handling is very important, especially for crypto code!
*
* How to use this code:
*
* Generating a Key
* ----------------
* try {
* $key = self::CreateNewRandomKey();
* // WARNING: Do NOT encode $key with bin2hex() or base64_encode(),
* // they may leak the key to the attacker through side channels.
* } catch (CryptoTestFailedException $ex) {
* die('Cannot safely create a key');
* } catch (CannotPerformOperationException $ex) {
* die('Cannot safely create a key');
* }
*
* Encrypting a Message
* --------------------
* $message = "ATTACK AT DAWN";
* try {
* $ciphertext = self::Encrypt($message, $key);
* } catch (CryptoTestFailedException $ex) {
* die('Cannot safely perform encryption');
* } catch (CannotPerformOperationException $ex) {
* die('Cannot safely perform decryption');
* }
*
* Decrypting a Message
* --------------------
* try {
* $decrypted = self::Decrypt($ciphertext, $key);
* } catch (InvalidCiphertextException $ex) { // VERY IMPORTANT
* // Either:
* // 1. The ciphertext was modified by the attacker,
* // 2. The key is wrong, or
* // 3. $ciphertext is not a valid ciphertext or was corrupted.
* // Assume the worst.
* die('DANGER! DANGER! The ciphertext has been tampered with!');
* } catch (CryptoTestFailedException $ex) {
* die('Cannot safely perform encryption');
* } catch (CannotPerformOperationException $ex) {
* die('Cannot safely perform decryption');
* }
*/
/*
* Raised by Decrypt() when one of the following conditions are met:
* - The key is wrong.
* - The ciphertext is invalid or not in the correct format.
* - The attacker modified the ciphertext.
*/
class InvalidCiphertextException extends Exception {}
/* If you see these, it means it is NOT SAFE to do encryption on your system. */
class CannotPerformOperationException extends Exception {}
class CryptoTestFailedException extends Exception {}
final class Crypto
{
// Ciphertext format: [____HMAC____][____IV____][____CIPHERTEXT____].
/* DO NOT CHANGE THESE CONSTANTS!
*
* We spent *weeks* testing this code, making sure it is as perfect and
* correct as possible. Are you going to do the same after making your
* changes? Probably not. Besides, any change to these constants will break
* the runtime tests, which are extremely important for your security.
* You're literally millions of times more likely to screw up your own
* security by changing something here than you are to fall victim to an
* 128-bit key brute-force attack. You're also breaking your own
* compatibility with future updates to this library, so you'll be left
* vulnerable if we ever find a security bug and release a fix.
*
* So, PLEASE, do not change these constants.
*/
const CIPHER = 'aes-128';
const KEY_BYTE_SIZE = 16;
const CIPHER_MODE = 'cbc';
const HASH_FUNCTION = 'sha256';
const MAC_BYTE_SIZE = 32;
const ENCRYPTION_INFO = 'DefusePHP|KeyForEncryption';
const AUTHENTICATION_INFO = 'DefusePHP|KeyForAuthentication';
/*
* Use this to generate a random encryption key.
*/
public static function CreateNewRandomKey()
{
self::RuntimeTest();
return self::SecureRandom(self::KEY_BYTE_SIZE);
}
/*
* Encrypts a message.
* $plaintext is the message to encrypt.
* $key is the encryption key, a value generated by CreateNewRandomKey().
* You MUST catch exceptions thrown by this function. See docs above.
*/
public static function Encrypt($plaintext, $key)
{
self::RuntimeTest();
if (self::our_strlen($key) !== self::KEY_BYTE_SIZE)
{
throw new CannotPerformOperationException("Bad key.");
}
$method = self::CIPHER.'-'.self::CIPHER_MODE;
self::EnsureFunctionExists('openssl_get_cipher_methods');
if (in_array($method, openssl_get_cipher_methods()) === FALSE) {
throw new CannotPerformOperationException("Cipher method not supported.");
}
// Generate a sub-key for encryption.
$keysize = self::KEY_BYTE_SIZE;
$ekey = self::HKDF(self::HASH_FUNCTION, $key, $keysize, self::ENCRYPTION_INFO);
// Generate a random initialization vector.
self::EnsureFunctionExists("openssl_cipher_iv_length");
$ivsize = openssl_cipher_iv_length($method);
if ($ivsize === FALSE || $ivsize <= 0) {
throw new CannotPerformOperationException();
}
$iv = self::SecureRandom($ivsize);
$ciphertext = $iv . self::PlainEncrypt($plaintext, $ekey, $iv);
// Generate a sub-key for authentication and apply the HMAC.
$akey = self::HKDF(self::HASH_FUNCTION, $key, self::KEY_BYTE_SIZE, self::AUTHENTICATION_INFO);
$auth = hash_hmac(self::HASH_FUNCTION, $ciphertext, $akey, true);
$ciphertext = $auth . $ciphertext;
return $ciphertext;
}
/*
* Decrypts a ciphertext.
* $ciphertext is the ciphertext to decrypt.
* $key is the key that the ciphertext was encrypted with.
* You MUST catch exceptions thrown by this function. See docs above.
*/
public static function Decrypt($ciphertext, $key)
{
self::RuntimeTest();
$method = self::CIPHER.'-'.self::CIPHER_MODE;
self::EnsureFunctionExists('openssl_get_cipher_methods');
if (in_array($method, openssl_get_cipher_methods()) === FALSE) {
throw new CannotPerformOperationException("Cipher method not supported.");
}
// Extract the HMAC from the front of the ciphertext.
if (self::our_strlen($ciphertext) <= self::MAC_BYTE_SIZE) {
throw new InvalidCiphertextException();
}
$hmac = self::our_substr($ciphertext, 0, self::MAC_BYTE_SIZE);
if ($hmac === FALSE) {
throw new CannotPerformOperationException();
}
$ciphertext = self::our_substr($ciphertext, self::MAC_BYTE_SIZE);
if ($ciphertext === FALSE) {
throw new CannotPerformOperationException();
}
// Regenerate the same authentication sub-key.
$akey = self::HKDF(self::HASH_FUNCTION, $key, self::KEY_BYTE_SIZE, self::AUTHENTICATION_INFO);
if (self::VerifyHMAC($hmac, $ciphertext, $akey))
{
// Regenerate the same encryption sub-key.
$keysize = self::KEY_BYTE_SIZE;
$ekey = self::HKDF(self::HASH_FUNCTION, $key, $keysize, self::ENCRYPTION_INFO);
// Extract the initialization vector from the ciphertext.
self::EnsureFunctionExists("openssl_cipher_iv_length");
$ivsize = openssl_cipher_iv_length($method);
if ($ivsize === FALSE || $ivsize <= 0) {
throw new CannotPerformOperationException();
}
if (self::our_strlen($ciphertext) <= $ivsize) {
throw new InvalidCiphertextException();
}
$iv = self::our_substr($ciphertext, 0, $ivsize);
if ($iv === FALSE) {
throw new CannotPerformOperationException();
}
$ciphertext = self::our_substr($ciphertext, $ivsize);
if ($ciphertext === FALSE) {
throw new CannotPerformOperationException();
}
$plaintext = self::PlainDecrypt($ciphertext, $ekey, $iv);
return $plaintext;
}
else
{
/*
* We throw an exception instead of returning FALSE because we want
* a script that doesn't handle this condition to CRASH, instead
* of thinking the ciphertext decrypted to the value FALSE.
*/
throw new InvalidCiphertextException();
}
}
/*
* Runs tests.
* Raises CannotPerformOperationException or CryptoTestFailedException if
* one of the tests fail. If any tests fails, your system is not capable of
* performing encryption, so make sure you fail safe in that case.
*/
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;
}
try {
$test_state = 2;
self::AESTestVector();
self::HMACTestVector();
self::HKDFTestVector();
self::TestEncryptDecrypt();
if (self::our_strlen(self::CreateNewRandomKey()) != self::KEY_BYTE_SIZE) {
throw new CryptoTestFailedException();
}
if (self::ENCRYPTION_INFO == self::AUTHENTICATION_INFO) {
throw new CryptoTestFailedException();
}
} catch (CryptoTestFailedException $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).
$test_state = 1;
}
/*
* Never call this method directly!
*/
private static function PlainEncrypt($plaintext, $key, $iv)
{
$method = self::CIPHER.'-'.self::CIPHER_MODE;
self::EnsureConstantExists("OPENSSL_RAW_DATA");
self::EnsureFunctionExists("openssl_encrypt");
$ciphertext = openssl_encrypt(
$plaintext,
$method,
$key,
OPENSSL_RAW_DATA,
$iv
);
if ($ciphertext === false) {
throw new CannotPerformOperationException();
}
return $ciphertext;
}
/*
* Never call this method directly!
*/
private static function PlainDecrypt($ciphertext, $key, $iv)
{
$method = self::CIPHER.'-'.self::CIPHER_MODE;
self::EnsureConstantExists("OPENSSL_RAW_DATA");
self::EnsureFunctionExists("openssl_encrypt");
$plaintext = openssl_decrypt(
$ciphertext,
$method,
$key,
OPENSSL_RAW_DATA,
$iv
);
if ($plaintext === FALSE) {
throw new CannotPerformOperationException();
}
return $plaintext;
}
/*
* Returns a random binary string of length $octets bytes.
*/
private static function SecureRandom($octets)
{
self::EnsureFunctionExists("openssl_random_pseudo_bytes");
$random = openssl_random_pseudo_bytes($octets, $crypto_strong);
if ($crypto_strong === FALSE) {
throw new CannotPerformOperationException();
} else {
return $random;
}
}
/*
* Use HKDF to derive multiple keys from one.
* http://tools.ietf.org/html/rfc5869
*/
private static function HKDF($hash, $ikm, $length, $info = '', $salt = NULL)
{
// Find the correct digest length as quickly as we can.
$digest_length = self::MAC_BYTE_SIZE;
if ($hash != self::HASH_FUNCTION) {
$digest_length = self::our_strlen(hash_hmac($hash, '', '', true));
}
// Sanity-check the desired output length.
if (empty($length) || !is_int($length) ||
$length < 0 || $length > 255 * $digest_length) {
throw new CannotPerformOperationException();
}
// "if [salt] not provided, is set to a string of HashLen zeroes."
if (is_null($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, $salt, true);
// HKDF-Expand:
// This check is useless, but it serves as a reminder to the spec.
if (self::our_strlen($prk) < $digest_length) {
throw new CannotPerformOperationException();
}
// T(0) = ''
$t = '';
$last_block = '';
for ($block_index = 1; self::our_strlen($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
$orm = self::our_substr($t, 0, $length);
if ($orm === FALSE) {
throw new CannotPerformOperationException();
}
return $orm;
}
private static function VerifyHMAC($correct_hmac, $message, $key)
{
$message_hmac = hash_hmac(self::HASH_FUNCTION, $message, $key, true);
// We can't just compare the strings with '==', since it would make
// timing attacks possible. We could use the XOR-OR constant-time
// comparison algorithm, but I'm not sure if that's good enough way up
// here in an interpreted language. So we use the method of HMACing the
// strings we want to compare with a random key, then comparing those.
// NOTE: This leaks information when the strings are not the same
// length, but they should always be the same length here. Enforce it:
if (self::our_strlen($correct_hmac) !== self::our_strlen($message_hmac)) {
throw new CannotPerformOperationException();
}
$blind = self::CreateNewRandomKey();
$message_compare = hash_hmac(self::HASH_FUNCTION, $message_hmac, $blind);
$correct_compare = hash_hmac(self::HASH_FUNCTION, $correct_hmac, $blind);
return $correct_compare === $message_compare;
}
private static function TestEncryptDecrypt()
{
$key = self::CreateNewRandomKey();
$data = "EnCrYpT EvErYThInG\x00\x00";
// Make sure encrypting then decrypting doesn't change the message.
$ciphertext = self::Encrypt($data, $key);
try {
$decrypted = self::Decrypt($ciphertext, $key);
} catch (InvalidCiphertextException $ex) {
// It's important to catch this and change it into a
// CryptoTestFailedException, otherwise a test failure could trick
// the user into thinking it's just an invalid ciphertext!
throw new CryptoTestFailedException();
}
if($decrypted !== $data)
{
throw new CryptoTestFailedException();
}
// Modifying the ciphertext: Appending a string.
try {
self::Decrypt($ciphertext . "a", $key);
throw new CryptoTestFailedException();
} catch (InvalidCiphertextException $e) { /* expected */ }
// Modifying the ciphertext: Changing an IV byte.
try {
$ciphertext[0] = chr((ord($ciphertext[0]) + 1) % 256);
self::Decrypt($ciphertext, $key);
throw new CryptoTestFailedException();
} catch (InvalidCiphertextException $e) { /* expected */ }
// Decrypting with the wrong key.
$key = self::CreateNewRandomKey();
$data = "abcdef";
$ciphertext = self::Encrypt($data, $key);
$wrong_key = self::CreateNewRandomKey();
try {
self::Decrypt($ciphertext, $wrong_key);
throw new CryptoTestFailedException();
} catch (InvalidCiphertextException $e) { /* expected */ }
// Ciphertext too small (shorter than HMAC).
$key = self::CreateNewRandomKey();
$ciphertext = str_repeat("A", self::MAC_BYTE_SIZE - 1);
try {
self::Decrypt($ciphertext, $key);
throw new CryptoTestFailedException();
} catch (InvalidCiphertextException $e) { /* expected */ }
}
private static function HKDFTestVector()
{
// HKDF test vectors from RFC 5869
// Test Case 1
$ikm = str_repeat("\x0b", 22);
$salt = self::hexToBytes("000102030405060708090a0b0c");
$info = self::hexToBytes("f0f1f2f3f4f5f6f7f8f9");
$length = 42;
$okm = self::hexToBytes(
"3cb25f25faacd57a90434f64d0362f2a" .
"2d2d0a90cf1a5a4c5db02d56ecc4c5bf" .
"34007208d5b887185865"
);
$computed_okm = self::HKDF("sha256", $ikm, $length, $info, $salt);
if ($computed_okm !== $okm) {
throw new CryptoTestFailedException();
}
// Test Case 7
$ikm = str_repeat("\x0c", 22);
$length = 42;
$okm = self::hexToBytes(
"2c91117204d745f3500d636a62f64f0a" .
"b3bae548aa53d423b0d1f27ebba6f5e5" .
"673a081d70cce7acfc48"
);
$computed_okm = self::HKDF("sha1", $ikm, $length);
if ($computed_okm !== $okm) {
throw new CryptoTestFailedException();
}
}
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(self::HASH_FUNCTION, $data, $key) != $correct) {
throw new CryptoTestFailedException();
}
}
private static function AESTestVector()
{
// AES CBC mode test vector from NIST SP 800-38A
$key = self::hexToBytes("2b7e151628aed2a6abf7158809cf4f3c");
$iv = self::hexToBytes("000102030405060708090a0b0c0d0e0f");
$plaintext = self::hexToBytes(
"6bc1bee22e409f96e93d7e117393172a" .
"ae2d8a571e03ac9c9eb76fac45af8e51" .
"30c81c46a35ce411e5fbc1191a0a52ef" .
"f69f2445df4f9b17ad2b417be66c3710"
);
$ciphertext = self::hexToBytes(
"7649abac8119b246cee98e9b12e9197d" .
"5086cb9b507219ee95db113a917678b2" .
"73bed6b8e3c1743b7116e69e22229516" .
"3ff1caa1681fac09120eca307586e1a7" .
/* Block due to padding. Not from NIST test vector.
Padding Block: 10101010101010101010101010101010
Ciphertext: 3ff1caa1681fac09120eca307586e1a7
(+) 2fe1dab1780fbc19021eda206596f1b7
AES 8cb82807230e1321d3fae00d18cc2012
*/
"8cb82807230e1321d3fae00d18cc2012"
);
$computed_ciphertext = self::PlainEncrypt($plaintext, $key, $iv);
if ($computed_ciphertext !== $ciphertext) {
throw new CryptoTestFailedException();
}
$computed_plaintext = self::PlainDecrypt($ciphertext, $key, $iv);
if ($computed_plaintext !== $plaintext) {
throw new CryptoTestFailedException();
}
}
/* WARNING: Do not call this function on secrets. It creates side channels. */
private static function hexToBytes($hex_string)
{
return pack("H*", $hex_string);
}
private static function EnsureConstantExists($name)
{
if (!defined($name)) {
throw new CannotPerformOperationException();
}
}
private static function EnsureFunctionExists($name)
{
if (!function_exists($name)) {
throw new CannotPerformOperationException();
}
}
/*
* We need these strlen() and substr() functions because when
* 'mbstring.func_overload' is set in php.ini, the standard strlen() and
* substr() are replaced by mb_strlen() and mb_substr().
*/
private static function our_strlen($str)
{
if (function_exists('mb_strlen')) {
$length = mb_strlen($str, '8bit');
if ($length === FALSE) {
throw new CannotPerformOperationException();
}
return $length;
} else {
return strlen($str);
}
}
private static function our_substr($str, $start, $length = NULL)
{
if (function_exists('mb_substr'))
{
// mb_substr($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) {
$length = self::our_strlen($str) - $start;
} else {
$length = -$start;
}
}
return mb_substr($str, $start, $length, '8bit');
}
// Unlike mb_substr(), substr() doesn't accept NULL for length
if (isset($length)) {
return substr($str, $start, $length);
} else {
return substr($str, $start);
}
}
}
/*
* We want to catch all uncaught exceptions that come from the Crypto class,
* since by default, PHP will leak the key in the stack trace from an uncaught
* exception. This is a really ugly hack, but I think it's justified.
*
* Everything up to handler() getting called should be reliable, so this should
* reliably suppress the stack traces. The rest is just a bonus so that we don't
* make it impossible to debug other exceptions.
*
* This bit of code was adapted from: http://stackoverflow.com/a/7939492
*/
class CryptoExceptionHandler
{
private $rethrow = NULL;
public function __construct()
{
set_exception_handler(array($this, "handler"));
}
public function handler($ex)
{
if (
$ex instanceof InvalidCiphertextException ||
$ex instanceof CannotPerformOperationException ||
$ex instanceof CryptoTestFailedException
) {
echo "FATAL ERROR: Uncaught crypto exception. Suppresssing output.\n";
} else {
/* Re-throw the exception in the destructor. */
$this->rethrow = $ex;
}
}
public function __destruct() {
if ($this->rethrow) {
throw $this->rethrow;
}
}
}
$crypto_exception_handler_object_dont_touch_me = new CryptoExceptionHandler();