function encrypt_aes_cbc($key, $data, $iv = '')
{
// mcrypt pads with null bytes, but Matasano implies desire for implementation of PKCS#7.
$ksize = mcrypt_get_key_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC);
$bsize = mcrypt_get_block_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_ECB);
$data = pad_pkcs7($data);
if (strlen($iv) != $bsize) {
echo 'Warning: IV must match block-size in length. Defaulting to null bytes.', PHP_EOL;
$iv = str_repeat("", $bsize);
}
if (strlen($key) > $ksize) {
die("Error: Maximum key-size for AES-128-CBC is {$ksize}." . PHP_EOL);
}
$blocks = str_split($data, $bsize);
$blocks[0] = mcrypt_ecb(MCRYPT_RIJNDAEL_128, $key, $blocks[0] ^ $iv, MCRYPT_ENCRYPT);
for ($i = 1, $j = count($blocks), $enc = $blocks[0]; $i < $j; $i++) {
$blocks[$i] ^= $blocks[$i - 1];
$blocks[$i] = mcrypt_ecb(MCRYPT_RIJNDAEL_128, $key, $blocks[$i], MCRYPT_ENCRYPT);
$enc .= $blocks[$i];
}
return $enc;
}
<?php
function strip_pkcs7($padded_str)
{
$len = strlen($padded_str);
$pad = ord($padded_str[$len - 1]);
if (substr($padded_str, $len - $pad) != str_repeat(chr($pad), $pad)) {
throw new Exception(__FUNCTION__ . '(): Bad padding.');
}
return substr($padded_str, 0, $len - $pad);
}
function pad_pkcs7($string)
{
$bsize = mcrypt_get_block_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_ECB);
$padding = $bsize - strlen($string) % $bsize;
$string .= str_repeat(chr($padding), $padding);
return $string;
}
$padded = pad_pkcs7('BANKAI!');
try {
echo strip_pkcs7($padded);
} catch (Exception $e) {
echo $e->getMessage(), PHP_EOL;
}
