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<?php // This PHP code snippet provides a basic understanding of // PHP's AES encryption. // The first thing to understand is the meaning of these constants: // MCRYPT_RIJNDAEL_128 // MCRYPT_RIJNDAEL_192 // MCRYPT_RIJNDAEL_256 // You would think that MCRYPT_RIJNDAEL_256 specifies 256-bit encryption, // but that is wrong. The three choices specify the block-size to be used // with Rijndael encryption. They say nothing about the key size (i.e. strength) // of the encryption. (Read further to understand how the strength of the // AES encryption is set.) // // The Rijndael encyrption algorithm is a block cipher. It operates on discrete // blocks of data. Padding MUST be added such that // the data to be encrypted has a length that is a multiple of the block size. // (PHP pads with NULL bytes) // Thus, if you specify MCRYPT_RIJNDAEL_256, your encrypted output will always // be a multiple of 32 bytes (i.e. 256 bits). If you specify MCRYPT_RIJNDAEL_128, // your encrypted output will always be a multiple of 16 bytes. // // Note: Strictly speaking, AES is not precisely Rijndael (although in practice // they are used interchangeably) as Rijndael supports a larger range of block // and key sizes; AES has a fixed block size of 128 bits and a key size of // 128, 192, or 256 bits, whereas Rijndael can be specified with key and block // sizes in any multiple of 32 bits, with a minimum of 128 bits and a maximum of // 256 bits. // In summary: If you want to be AES compliant, always choose MCRYPT_RIJNDAEL_128. // // So the first step is to create the cipher object: $cipher = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '', MCRYPT_MODE_CFB, ''); // We're using CBC mode (cipher-block chaining). Block cipher modes are detailed // here: http://en.wikipedia.org/wiki/Block_cipher_modes_of_operation // CBC mode requires an initialization vector. The size of the IV (initialization // vector) is always equal to the block-size. (It is NOT equal to the key size.) // Given that our block size is 128-bits, the IV is also 128-bits (i.e. 16 bytes). // Thus, for AES encryption, the IV is always 16 bytes regardless of the // strength of encryption. // // Here's some PHP code to verify our IV size: $iv_size = mcrypt_enc_get_iv_size($cipher); printf("iv_size = %d\n",$iv_size); // How do you do 256-bit AES encryption in PHP vs. 128-bit AES encryption??? // The answer is: Give it a key that's 32 bytes long as opposed to 16 bytes long. // For example: $key256 = 'a7fc844d17f43955783d7d6f5df7eb4e'; // Here's our 128-bit IV which is used for both 256-bit and 128-bit keys. $iv = '1234567890123456'; printf("iv: %s\n",bin2hex($iv)); printf("key256: %s\n",bin2hex($key256)); printf("key128: %s\n",bin2hex($key128)); // This is the plain-text to be encrypted: $cleartext = '5854889097648545'; printf("plainText: %s\n\n",$cleartext); // The mcrypt_generic_init function initializes the cipher by specifying both // the key and the IV. The length of the key determines whether we're doing // 128-bit, 192-bit, or 256-bit encryption. // Let's do 256-bit encryption here: if (mcrypt_generic_init($cipher, $key256, $iv) != -1) { // PHP pads with NULL bytes if $cleartext is not a multiple of the block size.. $cipherText = mcrypt_generic($cipher,$cleartext ); mcrypt_generic_deinit($cipher); // Display the result in hex. printf("256-bit encrypted result:\n%s\n\n",bin2hex($cipherText)); } // ------- // Results // ------- // You may use these as test vectors for testing your AES implementations... // // ------------------------ // 256-bit key, CBC mode // ------------------------ // IV = '1234567890123456' // (hex: 31323334353637383930313233343536) // Key = '12345678901234561234567890123456' // (hex: 3132333435363738393031323334353631323334353637383930313233343536) // PlainText: // 'The quick brown fox jumped over the lazy dog' // CipherText(hex): // 2fddc3abec692e1572d9b7d629172a05caf230bc7c8fd2d26ccfd65f9c54526984f7cb1c4326ef058cd7bee3967299e3 // // ------------------------ // 128-bit key, CBC mode // ------------------------ // IV = '1234567890123456' // (hex: 31323334353637383930313233343536) // Key = '1234567890123456' // (hex: 31323334353637383930313233343536) // PlainText: // 'The quick brown fox jumped over the lazy dog' // CipherText(hex): // f78176ae8dfe84578529208d30f446bbb29a64dc388b5c0b63140a4f316b3f341fe7d3b1a3cc5113c81ef8dd714a1c99 ?>