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<?php
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/**
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* OpensslStatic.php
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*
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* PHP version 7
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*
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* @category Dcrypt
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* @package Dcrypt
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* @author Michael Meyer (mmeyer2k) <[email protected]>
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* @license http://opensource.org/licenses/MIT The MIT License (MIT)
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* @link https://github.com/mmeyer2k/dcrypt
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*/
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namespace Dcrypt;
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class OpensslStatic
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{
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public static function decrypt(string $data, string $pass, string $cipher, string $algo): string
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{
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// Calculate the hash checksum size in bytes for the specified algo
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$hsz = Str::hashSize($algo);
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// Find the tag size for this cipher mode
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// Unless using GCM/CCM this will be zero
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$tsz = self::tagRequired($cipher) ? 4 : 0;
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// Ask openssl for the IV size needed for specified cipher
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$isz = OpensslWrapper::ivsize($cipher);
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// Find the IV at the beginning of the cypher text
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$ivr = Str::substr($data, 0, $isz);
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// Gather the checksum portion of the ciphertext
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$sum = Str::substr($data, $isz, $hsz);
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// Gather the GCM/CCM authentication tag
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$tag = Str::substr($data, $isz + $hsz, $tsz);
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// Gather the iterations portion of the cipher text as packed/encrytped unsigned long
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$itr = Str::substr($data, $isz + $hsz + $tsz, 4);
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// Gather message portion of ciphertext after iv and checksum
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$msg = Str::substr($data, $isz + $hsz + $tsz + 4);
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// Calculate verification checksum
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$chk = \hash_hmac($algo, ($msg . $itr . $ivr), $pass, true);
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// Verify HMAC before decrypting
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if (!Str::equal($chk, $sum)) {
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throw new \InvalidArgumentException('Decryption can not proceed due to invalid cyphertext checksum.');
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}
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// Decrypt and unpack the cost parameter to match what was used during encryption
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$cost = \unpack('N', $itr ^ \hash_hmac($algo, $ivr, $pass, true))[1];
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// Derive key from password
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$key = \hash_pbkdf2($algo, ($pass . $cipher), $ivr, $cost, 0, true);
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// Decrypt message and return
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return OpensslWrapper::decrypt($msg, $cipher, $key, $ivr, $tag);
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}
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public static function encrypt(string $data, string $pass, string $cipher, string $algo, int $cost = 1): string
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{
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// Generate IV of appropriate size.
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$ivr = \random_bytes(OpensslWrapper::ivsize($cipher));
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// Derive key from password with hash_pbkdf2 function.
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// Append CIPHER to password beforehand so that cross-method decryptions will fail at checksum step
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$key = \hash_pbkdf2($algo, ($pass . $cipher), $ivr, $cost, 0, true);
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// Create a placeholder for the authentication tag to be passed by reference
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$tag = '';
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// Encrypt the plaintext data
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$msg = OpensslWrapper::encrypt($data, $cipher, $key, $ivr, $tag);
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// Convert cost integer into 4 byte string and XOR it with a newly derived key
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$itr = \pack('N', $cost) ^ \hash_hmac($algo, $ivr, $pass, true);
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// Generate the ciphertext checksum to prevent bit tampering
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$chk = \hash_hmac($algo, ($msg . $itr . $ivr), $pass, true);
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// Return iv + checksum + iterations + cyphertext + tag
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return $ivr . $chk . $tag . $itr . $msg;
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}
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/**
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* Determines if the provided cipher requires a tag
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*
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* @param string $cipher
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* @return bool
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*/
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public static function tagRequired(string $cipher): bool
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{
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$cipher = strtolower($cipher);
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$needle_tips = [
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'-gcm',
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'-ccm',
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];
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foreach ($needle_tips as $needle) {
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if (strpos($cipher, $needle)) {
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return true;
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}
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}
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return false;
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}
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} |
mmeyer2k /
dcrypt
