<?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 $inc
*
* @throws Ex\EnvironmentIsBrokenException
*
* @return string
*
* @psalm-suppress RedundantCondition - It's valid to use is_int to check for overflow.
*/
public static function incrementCounter($ctr, $inc)
{
Core::ensureTrue(
Core::ourStrlen($ctr) === Core::BLOCK_BYTE_SIZE,
'Trying to increment a nonce of the wrong size.'
);
Core::ensureTrue(
\is_int($inc),
'Trying to increment nonce by a non-integer.'
);
// The caller is probably re-using CTR-mode keystream if they increment by 0.
Core::ensureTrue(
$inc > 0,
'Trying to increment a nonce by a nonpositive amount'
);
Core::ensureTrue(
$inc <= PHP_INT_MAX - 255,
'Integer overflow may occur'
);
/*
* We start at the rightmost byte (big-endian)
* So, too, does OpenSSL: http://stackoverflow.com/a/3146214/2224584
*/
for ($i = Core::BLOCK_BYTE_SIZE - 1; $i >= 0; --$i) {
$sum = \ord($ctr[$i]) + $inc;
/* Detect integer overflow and fail. */
Core::ensureTrue(\is_int($sum), '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)
{
if ($octets <= 0) {
throw new Ex\CryptoException(
'A zero or negative amount of random bytes was requested.'
);
}
self::ensureFunctionExists('random_bytes');
try {
return \random_bytes(max(1, $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 $salt
*
* @throws Ex\EnvironmentIsBrokenException
* @psalm-suppress UndefinedFunction - We're checking if the function exists first.
*
* @return string
*/
public static function HKDF($hash, $ikm, $length, $info = '', $salt = null)
{
static $nativeHKDF = null;
if ($nativeHKDF === null) {
$nativeHKDF = \is_callable('\\hash_hkdf');
}
if ($nativeHKDF) {
if (\is_null($salt)) {
$salt = '';
}
return \hash_hkdf($hash, $ikm, $length, $info, $salt);
}
$digest_length = Core::ourStrlen(\hash_hmac($hash, '', '', true));
// Sanity-check the desired output length.
Core::ensureTrue(
!empty($length) && \is_int($length) && $length >= 0 && $length <= 255 * $digest_length,
'Bad output length requested of HDKF.'
);
// "if [salt] not provided, is set to a string of HashLen zeroes."
if (\is_null($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, $salt, true);
// HKDF-Expand:
// This check is useless, but it serves as a reminder to the spec.
Core::ensureTrue(Core::ourStrlen($prk) >= $digest_length);
// 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
/** @var string $orm */
$orm = Core::ourSubstr($t, 0, $length);
Core::ensureTrue(\is_string($orm));
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, $given);
}
// We can't just compare the strings with '==', since it would make
// timing attacks possible. We could use the XOR-OR constant-time
// comparison algorithm, but that may not be a reliable defense in an
// interpreted language. So we use the approach of HMACing both strings
// with a random key and comparing the HMACs.
// We're not attempting to make variable-length string comparison
// secure, as that's very difficult. Make sure the strings are the same
// length.
Core::ensureTrue(Core::ourStrlen($expected) === Core::ourStrlen($given));
$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 $name
* @return void
*
* @throws Ex\EnvironmentIsBrokenException
*/
public static function ensureConstantExists($name)
{
Core::ensureTrue(
\defined($name),
'Constant '.$name.' does not exists'
);
}
/**
* Throws an exception if the function doesn't exist.
*
* @param string $name
* @return void
*
* @throws Ex\EnvironmentIsBrokenException
*/
public static function ensureFunctionExists($name)
{
Core::ensureTrue(
\function_exists($name),
'function '.$name.' does not exists'
);
}
/**
* Throws an exception if the condition is false.
*
* @param bool $condition
* @param string $message
* @return void
*
* @throws Ex\EnvironmentIsBrokenException
*/
public static function ensureTrue($condition, $message = '')
{
if (!$condition) {
throw new Ex\EnvironmentIsBrokenException($message);
}
}
/*
* 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) {
$exists = \extension_loaded('mbstring') && \function_exists('mb_strlen');
}
if ($exists) {
$length = \mb_strlen($str, '8bit');
Core::ensureTrue($length !== false);
return $length;
} else {
return \strlen($str);
}
}
/**
* Behaves roughly like the function substr() in PHP 7 does.
*
* @param string $str
* @param int $start
* @param int $length
*
* @throws Ex\EnvironmentIsBrokenException
*
* @return string|bool
*/
public static function ourSubstr($str, $start, $length = null)
{
static $exists = null;
if ($exists === null) {
$exists = \extension_loaded('mbstring') && \function_exists('mb_substr');
}
// 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.)
$input_len = Core::ourStrlen($str);
if ($start === $input_len && !$length) {
return '';
}
if ($start > $input_len) {
return false;
}
// mb_substr($str, 0, NULL, '8bit') returns an empty string on PHP 5.3,
// so we have to find the length ourselves. Also, substr() doesn't
// accept null for the length.
if (! isset($length)) {
if ($start >= 0) {
$length = $input_len - $start;
} else {
$length = -$start;
}
}
if ($length < 0) {
throw new \InvalidArgumentException(
"Negative lengths are not supported with ourSubstr."
);
}
if ($exists) {
$substr = \mb_substr($str, $start, $length, '8bit');
// At this point there are two cases where mb_substr can
// legitimately return an empty string. Either $length is 0, or
// $start is equal to the length of the string (both mb_substr and
// substr return an empty string when this happens). It should never
// ever return a string that's longer than $length.
if (Core::ourStrlen($substr) > $length || (Core::ourStrlen($substr) === 0 && $length !== 0 && $start !== $input_len)) {
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 $substr;
}
return \substr($str, $start, $length);
}
/**
* 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,
#[\SensitiveParameter]
$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);
Core::ensureTrue(
\in_array($algorithm, \hash_algos(), true),
'Invalid or unsupported hash algorithm.'
);
// Whitelist, or we could end up with people using CRC32.
$ok_algorithms = [
'sha1', 'sha224', 'sha256', 'sha384', 'sha512',
'ripemd160', 'ripemd256', 'ripemd320', 'whirlpool',
];
Core::ensureTrue(
\in_array($algorithm, $ok_algorithms, true),
'Algorithm is not a secure cryptographic hash function.'
);
Core::ensureTrue($count > 0 && $key_length > 0, '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++) {
/**
* @psalm-suppress InvalidOperand
*/
$xorsum ^= ($last = \hash_hmac($algorithm, $last, $password, true));
}
$output .= $xorsum;
}
if ($raw_output) {
return (string) Core::ourSubstr($output, 0, $key_length);
} else {
return Encoding::binToHex((string) Core::ourSubstr($output, 0, $key_length));
}
}
}
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