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/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */ |
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/* AES counter (CTR) mode implementation in PHP (c) Chris Veness 2005-2010. Right of free use is */ |
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/* granted for all commercial or non-commercial use under CC-BY licence. No warranty of any */ |
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/* form is offered. */ |
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/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */ |
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View Code Duplication |
class AesCtr extends Aes |
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{ |
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/** |
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* Encrypt a text using AES encryption in Counter mode of operation |
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* - see http://csrc.nist.gov/publications/nistpubs/800-38a/sp800-38a.pdf |
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* |
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* Unicode multi-byte character safe |
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* |
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* @param plaintext source text to be encrypted |
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* @param password the password to use to generate a key |
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* @param nBits number of bits to be used in the key (128, 192, or 256) |
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* @return string text |
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*/ |
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public static function encrypt($plaintext, $password, $nBits) |
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{ |
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$blockSize = 16; // block size fixed at 16 bytes / 128 bits (Nb=4) for AES |
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if (!($nBits == 128 || $nBits == 192 || $nBits == 256)) { |
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return ''; |
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} |
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// standard allows 128/192/256 bit keys |
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// note PHP (5) gives us plaintext and password in UTF8 encoding! |
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// use AES itself to encrypt password to get cipher key (using plain password as source for |
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// key expansion) - gives us well encrypted key |
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$nBytes = $nBits / 8; // no bytes in key |
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$pwBytes = array(); |
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for ($i = 0; $i < $nBytes; $i++) { |
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$pwBytes[$i] = ord(substr($password, $i, 1)) & 0xff; |
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} |
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$key = Aes::cipher($pwBytes, Aes::keyExpansion($pwBytes)); |
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$key = array_merge($key, array_slice($key, 0, $nBytes - 16)); // expand key to 16/24/32 bytes long |
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// initialise counter block (NIST SP800-38A §B.2): millisecond time-stamp for nonce in |
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// 1st 8 bytes, block counter in 2nd 8 bytes |
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$counterBlock = array(); |
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$nonce = floor(microtime(true) * 1000); // timestamp: milliseconds since 1-Jan-1970 |
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$nonceSec = floor($nonce / 1000); |
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$nonceMs = $nonce % 1000; |
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// encode nonce with seconds in 1st 4 bytes, and (repeated) ms part filling 2nd 4 bytes |
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for ($i = 0; $i < 4; $i++) { |
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$counterBlock[$i] = self::urs($nonceSec, $i * 8) & 0xff; |
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} |
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for ($i = 0; $i < 4; $i++) { |
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$counterBlock[$i + 4] = $nonceMs & 0xff; |
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} |
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// and convert it to a string to go on the front of the ciphertext |
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$ctrTxt = ''; |
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for ($i = 0; $i < 8; $i++) { |
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$ctrTxt .= chr($counterBlock[$i]); |
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} |
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// generate key schedule - an expansion of the key into distinct Key Rounds for each round |
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$keySchedule = Aes::keyExpansion($key); |
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//print_r($keySchedule); |
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$blockCount = ceil(strlen($plaintext) / $blockSize); |
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$ciphertxt = array(); // ciphertext as array of strings |
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for ($b = 0; $b < $blockCount; $b++) { |
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// set counter (block #) in last 8 bytes of counter block (leaving nonce in 1st 8 bytes) |
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// done in two stages for 32-bit ops: using two words allows us to go past 2^32 blocks (68GB) |
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for ($c = 0; $c < 4; $c++) { |
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$counterBlock[15 - $c] = self::urs($b, $c * 8) & 0xff; |
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} |
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for ($c = 0; $c < 4; $c++) { |
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$counterBlock[15 - $c - 4] = self::urs($b / 0x100000000, $c * 8); |
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} |
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$cipherCntr = Aes::cipher($counterBlock, $keySchedule); // -- encrypt counter block -- |
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// block size is reduced on final block |
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$blockLength = $b < $blockCount - 1 ? $blockSize : (strlen($plaintext) - 1) % $blockSize + 1; |
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$cipherByte = array(); |
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for ($i = 0; $i < $blockLength; $i++) { // -- xor plaintext with ciphered counter byte-by-byte -- |
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$cipherByte[$i] = $cipherCntr[$i] ^ ord(substr($plaintext, $b * $blockSize + $i, 1)); |
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$cipherByte[$i] = chr($cipherByte[$i]); |
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} |
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$ciphertxt[$b] = implode('', $cipherByte); // escape troublesome characters in ciphertext |
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} |
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// implode is more efficient than repeated string concatenation |
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$ciphertext = $ctrTxt.implode('', $ciphertxt); |
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$ciphertext = base64_encode($ciphertext); |
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return $ciphertext; |
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} |
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/** |
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* Decrypt a text encrypted by AES in counter mode of operation |
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* |
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* @param ciphertext source text to be decrypted |
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* @param password the password to use to generate a key |
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* @param nBits number of bits to be used in the key (128, 192, or 256) |
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* @return string text |
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*/ |
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public static function decrypt($ciphertext, $password, $nBits) |
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{ |
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$blockSize = 16; // block size fixed at 16 bytes / 128 bits (Nb=4) for AES |
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if (!($nBits == 128 || $nBits == 192 || $nBits == 256)) { |
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return ''; |
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} |
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// standard allows 128/192/256 bit keys |
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$ciphertext = base64_decode($ciphertext); |
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// use AES to encrypt password (mirroring encrypt routine) |
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$nBytes = $nBits / 8; // no bytes in key |
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$pwBytes = array(); |
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for ($i = 0; $i < $nBytes; $i++) { |
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$pwBytes[$i] = ord(substr($password, $i, 1)) & 0xff; |
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} |
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$key = Aes::cipher($pwBytes, Aes::keyExpansion($pwBytes)); |
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$key = array_merge($key, array_slice($key, 0, $nBytes - 16)); // expand key to 16/24/32 bytes long |
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// recover nonce from 1st element of ciphertext |
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$counterBlock = array(); |
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$ctrTxt = substr($ciphertext, 0, 8); |
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for ($i = 0; $i < 8; $i++) { |
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$counterBlock[$i] = ord(substr($ctrTxt, $i, 1)); |
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} |
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// generate key schedule |
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$keySchedule = Aes::keyExpansion($key); |
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// separate ciphertext into blocks (skipping past initial 8 bytes) |
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$nBlocks = ceil((strlen($ciphertext) - 8) / $blockSize); |
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$ct = array(); |
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for ($b = 0; $b < $nBlocks; $b++) { |
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$ct[$b] = substr($ciphertext, 8 + $b * $blockSize, 16); |
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} |
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$ciphertext = $ct; // ciphertext is now array of block-length strings |
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// plaintext will get generated block-by-block into array of block-length strings |
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$plaintxt = array(); |
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for ($b = 0; $b < $nBlocks; $b++) { |
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// set counter (block #) in last 8 bytes of counter block (leaving nonce in 1st 8 bytes) |
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for ($c = 0; $c < 4; $c++) { |
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$counterBlock[15 - $c] = self::urs($b, $c * 8) & 0xff; |
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} |
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for ($c = 0; $c < 4; $c++) { |
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$counterBlock[15 - $c - 4] = self::urs(($b + 1) / 0x100000000 - 1, $c * 8) & 0xff; |
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} |
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$cipherCntr = Aes::cipher($counterBlock, $keySchedule); // encrypt counter block |
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$plaintxtByte = array(); |
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for ($i = 0; $i < strlen($ciphertext[$b]); $i++) { |
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// -- xor plaintext with ciphered counter byte-by-byte -- |
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$plaintxtByte[$i] = $cipherCntr[$i] ^ ord(substr($ciphertext[$b], $i, 1)); |
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$plaintxtByte[$i] = chr($plaintxtByte[$i]); |
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} |
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$plaintxt[$b] = implode('', $plaintxtByte); |
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} |
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// join array of blocks into single plaintext string |
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$plaintext = implode('', $plaintxt); |
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return $plaintext; |
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} |
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/* |
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* Unsigned right shift function, since PHP has neither >>> operator nor unsigned ints |
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* |
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* @param a number to be shifted (32-bit integer) |
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* @param b number of bits to shift a to the right (0..31) |
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* @return a right-shifted and zero-filled by b bits |
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*/ |
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private static function urs($a, $b) |
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{ |
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$a &= 0xffffffff; $b &= 0x1f; // (bounds check) |
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if ($a & 0x80000000 && $b > 0) { // if left-most bit set |
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$a = ($a >> 1) & 0x7fffffff; // right-shift one bit & clear left-most bit |
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$a = $a >> ($b - 1); // remaining right-shifts |
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} else { // otherwise |
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$a = ($a >> $b); // use normal right-shift |
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} |
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return $a; |
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} |
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} |
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/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */ |
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Duplicated code is one of the most pungent code smells. If you need to duplicate the same code in three or more different places, we strongly encourage you to look into extracting the code into a single class or operation.
You can also find more detailed suggestions in the “Code” section of your repository.