I am coding an Android client of a web game. We need to transfer data in AES encrypted. But it has to be a specified key. For example, “0” is the key when client login.
and after that ,the key will be session_id, which I get from server with the login response.
But, the length of the key of AES they use is actually 256 bit. To expand “0” to that length, they use an algorithm i don’t know what. I need to do this in a similar way in Java.
They gave me the php file they used in there Flash client. How do I AES that in Java?
<?php
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
/* AES implementation in PHP (c) Chris Veness 2005-2009. Right of free use is granted for all */
/* commercial or non-commercial use under LGPL licence. No warranty of any form is offered. */
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
/**
* AES Cipher function: encrypt 'input' with Rijndael algorithm
*
* @param input message as byte-array (16 bytes)
* @param w key schedule as 2D byte-array (Nr+1 x Nb bytes) -
* generated from the cipher key by KeyExpansion()
* @return ciphertext as byte-array (16 bytes)
*/
function Cipher($input, $w) { // main Cipher function [§5.1]
$Nb = 4; // block size (in words): no of columns in state (fixed at 4 for AES)
$Nr = count($w)/$Nb - 1; // no of rounds: 10/12/14 for 128/192/256-bit keys
$state = array(); // initialise 4xNb byte-array 'state' with input [§3.4]
for ($i=0; $i<4*$Nb; $i++) $state[$i%4][floor($i/4)] = $input[$i];
$state = AddRoundKey($state, $w, 0, $Nb);
for ($round=1; $round<$Nr; $round++) { // apply Nr rounds
$state = SubBytes($state, $Nb);
$state = ShiftRows($state, $Nb);
$state = MixColumns($state, $Nb);
$state = AddRoundKey($state, $w, $round, $Nb);
}
$state = SubBytes($state, $Nb);
$state = ShiftRows($state, $Nb);
$state = AddRoundKey($state, $w, $Nr, $Nb);
$output = array(4*$Nb); // convert state to 1-d array before returning [§3.4]
for ($i=0; $i<4*$Nb; $i++) $output[$i] = $state[$i%4][floor($i/4)];
return $output;
}
function AddRoundKey($state, $w, $rnd, $Nb) { // xor Round Key into state S [§5.1.4]
for ($r=0; $r<4; $r++) {
for ($c=0; $c<$Nb; $c++) $state[$r][$c] ^= $w[$rnd*4+$c][$r];
}
return $state;
}
function SubBytes($s, $Nb) { // apply SBox to state S [§5.1.1]
global $Sbox; // PHP needs explicit declaration to access global variables!
for ($r=0; $r<4; $r++) {
for ($c=0; $c<$Nb; $c++) $s[$r][$c] = $Sbox[$s[$r][$c]];
}
return $s;
}
function ShiftRows($s, $Nb) { // shift row r of state S left by r bytes [§5.1.2]
$t = array(4);
for ($r=1; $r<4; $r++) {
for ($c=0; $c<4; $c++) $t[$c] = $s[$r][($c+$r)%$Nb]; // shift into temp copy
for ($c=0; $c<4; $c++) $s[$r][$c] = $t[$c]; // and copy back
} // note that this will work for Nb=4,5,6, but not 7,8 (always 4 for AES):
return $s; // see fp.gladman.plus.com/cryptography_technology/rijndael/aes.spec.311.pdf
}
function MixColumns($s, $Nb) { // combine bytes of each col of state S [§5.1.3]
for ($c=0; $c<4; $c++) {
$a = array(4); // 'a' is a copy of the current column from 's'
$b = array(4); // 'b' is a?{02} in GF(2^8)
for ($i=0; $i<4; $i++) {
$a[$i] = $s[$i][$c];
$b[$i] = $s[$i][$c]&0x80 ? $s[$i][$c]<<1 ^ 0x011b : $s[$i][$c]<<1;
}
// a[n] ^ b[n] is a?{03} in GF(2^8)
$s[0][$c] = $b[0] ^ $a[1] ^ $b[1] ^ $a[2] ^ $a[3]; // 2*a0 + 3*a1 + a2 + a3
$s[1][$c] = $a[0] ^ $b[1] ^ $a[2] ^ $b[2] ^ $a[3]; // a0 * 2*a1 + 3*a2 + a3
$s[2][$c] = $a[0] ^ $a[1] ^ $b[2] ^ $a[3] ^ $b[3]; // a0 + a1 + 2*a2 + 3*a3
$s[3][$c] = $a[0] ^ $b[0] ^ $a[1] ^ $a[2] ^ $b[3]; // 3*a0 + a1 + a2 + 2*a3
}
return $s;
}
/**
* Key expansion for Rijndael Cipher(): performs key expansion on cipher key
* to generate a key schedule
*
* @param key cipher key byte-array (16 bytes)
* @return key schedule as 2D byte-array (Nr+1 x Nb bytes)
*/
function KeyExpansion($key) { // generate Key Schedule from Cipher Key [§5.2]
global $Rcon; // PHP needs explicit declaration to access global variables!
$Nb = 4; // block size (in words): no of columns in state (fixed at 4 for AES)
$Nk = count($key)/4; // key length (in words): 4/6/8 for 128/192/256-bit keys
$Nr = $Nk + 6; // no of rounds: 10/12/14 for 128/192/256-bit keys
$w = array();
$temp = array();
for ($i=0; $i<$Nk; $i++) {
$r = array($key[4*$i], $key[4*$i+1], $key[4*$i+2], $key[4*$i+3]);
$w[$i] = $r;
}
for ($i=$Nk; $i<($Nb*($Nr+1)); $i++) {
$w[$i] = array();
for ($t=0; $t<4; $t++) $temp[$t] = $w[$i-1][$t];
if ($i % $Nk == 0) {
$temp = SubWord(RotWord($temp));
for ($t=0; $t<4; $t++) $temp[$t] ^= $Rcon[$i/$Nk][$t];
} else if ($Nk > 6 && $i%$Nk == 4) {
$temp = SubWord($temp);
}
for ($t=0; $t<4; $t++) $w[$i][$t] = $w[$i-$Nk][$t] ^ $temp[$t];
}
return $w;
}
function SubWord($w) { // apply SBox to 4-byte word w
global $Sbox; // PHP needs explicit declaration to access global variables!
for ($i=0; $i<4; $i++) $w[$i] = $Sbox[$w[$i]];
return $w;
}
function RotWord($w) { // rotate 4-byte word w left by one byte
$tmp = $w[0];
for ($i=0; $i<3; $i++) $w[$i] = $w[$i+1];
$w[3] = $tmp;
return $w;
}
// Sbox is pre-computed multiplicative inverse in GF(2^8) used in SubBytes and KeyExpansion [§5.1.1]
$Sbox = array(0x63,0x7c,0x77,0x7b,0xf2,0x6b,0x6f,0xc5,0x30,0x01,0x67,0x2b,0xfe,0xd7,0xab,0x76,
0xca,0x82,0xc9,0x7d,0xfa,0x59,0x47,0xf0,0xad,0xd4,0xa2,0xaf,0x9c,0xa4,0x72,0xc0,
0xb7,0xfd,0x93,0x26,0x36,0x3f,0xf7,0xcc,0x34,0xa5,0xe5,0xf1,0x71,0xd8,0x31,0x15,
0x04,0xc7,0x23,0xc3,0x18,0x96,0x05,0x9a,0x07,0x12,0x80,0xe2,0xeb,0x27,0xb2,0x75,
0x09,0x83,0x2c,0x1a,0x1b,0x6e,0x5a,0xa0,0x52,0x3b,0xd6,0xb3,0x29,0xe3,0x2f,0x84,
0x53,0xd1,0x00,0xed,0x20,0xfc,0xb1,0x5b,0x6a,0xcb,0xbe,0x39,0x4a,0x4c,0x58,0xcf,
0xd0,0xef,0xaa,0xfb,0x43,0x4d,0x33,0x85,0x45,0xf9,0x02,0x7f,0x50,0x3c,0x9f,0xa8,
0x51,0xa3,0x40,0x8f,0x92,0x9d,0x38,0xf5,0xbc,0xb6,0xda,0x21,0x10,0xff,0xf3,0xd2,
0xcd,0x0c,0x13,0xec,0x5f,0x97,0x44,0x17,0xc4,0xa7,0x7e,0x3d,0x64,0x5d,0x19,0x73,
0x60,0x81,0x4f,0xdc,0x22,0x2a,0x90,0x88,0x46,0xee,0xb8,0x14,0xde,0x5e,0x0b,0xdb,
0xe0,0x32,0x3a,0x0a,0x49,0x06,0x24,0x5c,0xc2,0xd3,0xac,0x62,0x91,0x95,0xe4,0x79,
0xe7,0xc8,0x37,0x6d,0x8d,0xd5,0x4e,0xa9,0x6c,0x56,0xf4,0xea,0x65,0x7a,0xae,0x08,
0xba,0x78,0x25,0x2e,0x1c,0xa6,0xb4,0xc6,0xe8,0xdd,0x74,0x1f,0x4b,0xbd,0x8b,0x8a,
0x70,0x3e,0xb5,0x66,0x48,0x03,0xf6,0x0e,0x61,0x35,0x57,0xb9,0x86,0xc1,0x1d,0x9e,
0xe1,0xf8,0x98,0x11,0x69,0xd9,0x8e,0x94,0x9b,0x1e,0x87,0xe9,0xce,0x55,0x28,0xdf,
0x8c,0xa1,0x89,0x0d,0xbf,0xe6,0x42,0x68,0x41,0x99,0x2d,0x0f,0xb0,0x54,0xbb,0x16);
// Rcon is Round Constant used for the Key Expansion [1st col is 2^(r-1) in GF(2^8)] [§5.2]
$Rcon = array( array(0x00, 0x00, 0x00, 0x00),
array(0x01, 0x00, 0x00, 0x00),
array(0x02, 0x00, 0x00, 0x00),
array(0x04, 0x00, 0x00, 0x00),
array(0x08, 0x00, 0x00, 0x00),
array(0x10, 0x00, 0x00, 0x00),
array(0x20, 0x00, 0x00, 0x00),
array(0x40, 0x00, 0x00, 0x00),
array(0x80, 0x00, 0x00, 0x00),
array(0x1b, 0x00, 0x00, 0x00),
array(0x36, 0x00, 0x00, 0x00) );
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
/**
* Encrypt a text using AES encryption in Counter mode of operation
* - see http://csrc.nist.gov/publications/nistpubs/800-38a/sp800-38a.pdf
*
* Unicode multi-byte character safe
*
* @param plaintext source text to be encrypted
* @param password the password to use to generate a key
* @param nBits number of bits to be used in the key (128, 192, or 256)
* @return encrypted text
*/
function AESEncryptCtr($plaintext, $password, $nBits) {
$blockSize = 16; // block size fixed at 16 bytes / 128 bits (Nb=4) for AES
if (!($nBits==128 || $nBits==192 || $nBits==256)) return ''; // standard allows 128/192/256 bit keys
// note PHP (5) gives us plaintext and password in UTF8 encoding!
// use AES itself to encrypt password to get cipher key (using plain password as source for
// key expansion) - gives us well encrypted key
$nBytes = $nBits/8; // no bytes in key
$pwBytes = array();
for ($i=0; $i<$nBytes; $i++) $pwBytes[$i] = ord(substr($password,$i,1)) & 0xff;
$key = Cipher($pwBytes, KeyExpansion($pwBytes));
$key = array_merge($key, array_slice($key, 0, $nBytes-16)); // expand key to 16/24/32 bytes long
// initialise counter block (NIST SP800-38A §B.2): millisecond time-stamp for nonce in
// 1st 8 bytes, block counter in 2nd 8 bytes
$counterBlock = array();
$nonce = floor(microtime(true)*1000); // timestamp: milliseconds since 1-Jan-1970
$nonceSec = floor($nonce/1000);
$nonceMs = $nonce%1000;
// encode nonce with seconds in 1st 4 bytes, and (repeated) ms part filling 2nd 4 bytes
for ($i=0; $i<4; $i++) $counterBlock[$i] = urs($nonceSec, $i*8) & 0xff;
for ($i=0; $i<4; $i++) $counterBlock[$i+4] = $nonceMs & 0xff;
// and convert it to a string to go on the front of the ciphertext
$ctrTxt = '';
for ($i=0; $i<8; $i++) $ctrTxt .= chr($counterBlock[$i]);
// generate key schedule - an expansion of the key into distinct Key Rounds for each round
$keySchedule = KeyExpansion($key);
$blockCount = ceil(strlen($plaintext)/$blockSize);
$ciphertxt = array(); // ciphertext as array of strings
for ($b=0; $b<$blockCount; $b++) {
// set counter (block #) in last 8 bytes of counter block (leaving nonce in 1st 8 bytes)
// done in two stages for 32-bit ops: using two words allows us to go past 2^32 blocks (68GB)
for ($c=0; $c<4; $c++) $counterBlock[15-$c] = urs($b, $c*8) & 0xff;
for ($c=0; $c<4; $c++) $counterBlock[15-$c-4] = urs($b/0x100000000, $c*8);
$cipherCntr = Cipher($counterBlock, $keySchedule); // -- encrypt counter block --
// block size is reduced on final block
$blockLength = $b<$blockCount-1 ? $blockSize : (strlen($plaintext)-1)%$blockSize+1;
$cipherByte = array();
for ($i=0; $i<$blockLength; $i++) { // -- xor plaintext with ciphered counter byte-by-byte --
$cipherByte[$i] = $cipherCntr[$i] ^ ord(substr($plaintext, $b*$blockSize+$i, 1));
$cipherByte[$i] = chr($cipherByte[$i]);
}
$ciphertxt[$b] = implode('', $cipherByte); // escape troublesome characters in ciphertext
}
// implode is more efficient than repeated string concatenation
$ciphertext = $ctrTxt . implode('', $ciphertxt);
$ciphertext = base64_encode($ciphertext);
return $ciphertext;
}
/**
* Decrypt a text encrypted by AES in counter mode of operation
*
* @param ciphertext source text to be decrypted
* @param password the password to use to generate a key
* @param nBits number of bits to be used in the key (128, 192, or 256)
* @return decrypted text
*/
function AESDecryptCtr($ciphertext, $password, $nBits) {
$blockSize = 16; // block size fixed at 16 bytes / 128 bits (Nb=4) for AES
if (!($nBits==128 || $nBits==192 || $nBits==256)) return ''; // standard allows 128/192/256 bit keys
$ciphertext = base64_decode($ciphertext);
// use AES to encrypt password (mirroring encrypt routine)
$nBytes = $nBits/8; // no bytes in key
$pwBytes = array();
for ($i=0; $i<$nBytes; $i++) $pwBytes[$i] = ord(substr($password,$i,1)) & 0xff;
$key = Cipher($pwBytes, KeyExpansion($pwBytes));
$key = array_merge($key, array_slice($key, 0, $nBytes-16)); // expand key to 16/24/32 bytes long
// recover nonce from 1st element of ciphertext
$counterBlock = array();
$ctrTxt = substr($ciphertext, 0, 8);
for ($i=0; $i<8; $i++) $counterBlock[$i] = ord(substr($ctrTxt,$i,1));
// generate key schedule
$keySchedule = KeyExpansion($key);
// separate ciphertext into blocks (skipping past initial 8 bytes)
$nBlocks = ceil((strlen($ciphertext)-8) / $blockSize);
$ct = array();
for ($b=0; $b<$nBlocks; $b++) $ct[$b] = substr($ciphertext, 8+$b*$blockSize, 16);
$ciphertext = $ct; // ciphertext is now array of block-length strings
// plaintext will get generated block-by-block into array of block-length strings
$plaintxt = array();
for ($b=0; $b<$nBlocks; $b++) {
// set counter (block #) in last 8 bytes of counter block (leaving nonce in 1st 8 bytes)
for ($c=0; $c<4; $c++) $counterBlock[15-$c] = urs($b, $c*8) & 0xff;
for ($c=0; $c<4; $c++) $counterBlock[15-$c-4] = urs(($b+1)/0x100000000-1, $c*8) & 0xff;
$cipherCntr = Cipher($counterBlock, $keySchedule); // encrypt counter block
$plaintxtByte = array();
for ($i=0; $i<strlen($ciphertext[$b]); $i++) {
// -- xor plaintext with ciphered counter byte-by-byte --
$plaintxtByte[$i] = $cipherCntr[$i] ^ ord(substr($ciphertext[$b],$i,1));
$plaintxtByte[$i] = chr($plaintxtByte[$i]);
}
$plaintxt[$b] = implode('', $plaintxtByte);
}
// join array of blocks into single plaintext string
$plaintext = implode('',$plaintxt);
return $plaintext;
}
/*
* Unsigned right shift function, since PHP has neither >>> operator nor unsigned ints
*
* @param a number to be shifted (32-bit integer)
* @param b number of bits to shift a to the right (0..31)
* @return a right-shifted and zero-filled by b bits
*/
function urs($a, $b) {
$a &= 0xffffffff; $b &= 0x1f; // (bounds check)
if ($a&0x80000000 && $b>0) { // if left-most bit set
$a = ($a>>1) & 0x7fffffff; // right-shift one bit & clear left-most bit
$a = $a >> ($b-1); // remaining right-shifts
} else { // otherwise
$a = ($a>>$b); // use normal right-shift
}
return $a;
}
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
?>
The bulk of this looks like the code for AES itself. We don’t need to see that and nor do you because that is library code.
The key generation part of your code seems to be this:
I suggest you try to reproduce that part in Java to check that identical keys are generated from identical input.