I Have just found this on siamnet: hope this is of some use
<?php
function get_rnd_iv ($iv_len) {
$iv = '';
while ($iv_len-- > 0) {
$iv .= chr(mt_rand() & 0xff);
}
return $iv;
}
function md5_encrypt ($plain_text, $password, $iv_len = 16) {
$plain_text .= "\x13";
$n = strlen($plain_text);
if ($n % 16) $plain_text .= str_repeat("\0", 16 - ($n % 16));
$i = 0;
$enc_text = get_rnd_iv($iv_len);
$iv = substr($password ^ $enc_text, 0, 512);
while ($i < $n) {
$block = substr($plain_text, $i, 16) ^ pack('H*', md5($iv));
$enc_text .= $block;
$iv = substr($block . $iv, 0, 512) ^ $password;
$i += 16;
}
return base64_encode($enc_text);
}
function md5_decrypt ($enc_text, $password, $iv_len = 16) {
$enc_text = base64_decode($enc_text);
$n = strlen($enc_text);
$i = $iv_len;
$plain_text = '';
$iv = substr($password ^ substr($enc_text, 0, $iv_len), 0, 512);
while ($i < $n) {
$block = substr($enc_text, $i, 16);
$plain_text .= $block ^ pack('H*', md5($iv));
$iv = substr($block . $iv, 0, 512) ^ $password;
$i += 16;
}
return preg_replace('/\\x13\\x00*$/', '', $plain_text);
}
// split and encrypt file
#$file = "test.txt";
$file = "u/robot.png";
$filesize = filesize($file);
$salt = "Th1s Is a gr3aT sALT!!!";
$numberOfFiles = 3;
$handle = fopen($file, "r");
$sizePerSplitFile = ceil($filesize / $numberOfFiles);
exec("split --bytes={$sizePerSplitFile} {$file} {$file}-");
$a_splits = glob("{$file}-*");
$encFileContents = "";
foreach ($a_splits as $k=>$files) {
$encFileContents = md5_encrypt(file_get_contents($files), $salt);
file_put_contents($files, $encFileContents);
}
// decrypt and un-split file
$decryptedFile = "e/robot.png";
$encFileContents = "";
foreach ($a_splits as $k=>$files) {
$encFileContents .= md5_decrypt(file_get_contents($files), $salt);
}
file_put_contents($decryptedFile, $encFileContents);
