PHP Encryption

<?php
function encrypt_string($input, $key) {
  $key = substr(md5($key),0,24);
  $td = mcrypt_module_open ('tripledes', '', 'ecb', '');
  $iv = mcrypt_create_iv (mcrypt_enc_get_iv_size ($td), MCRYPT_RAND);
  mcrypt_generic_init ($td, $key, $iv);
  $encrypted_data = mcrypt_generic ($td, gzdeflate($input, 9));
  mcrypt_generic_deinit ($td);
  mcrypt_module_close ($td);
  return trim(str_rot13(base64_encode($encrypted_data)));
}

function decrypt_string($input, $key) {
  $input = trim(base64_decode(str_rot13($input)));
  $td = mcrypt_module_open ('tripledes', '', 'ecb', '');
  $key = substr(md5($key),0,24);
  $iv = mcrypt_create_iv (mcrypt_enc_get_iv_size ($td), MCRYPT_RAND);
  mcrypt_generic_init ($td, $key, $iv);
  $decrypted_data = mdecrypt_generic ($td, $input);
  mcrypt_generic_deinit ($td);
  mcrypt_module_close ($td);
  return stripslashes(trim(@gzinflate($decrypted_data)));
}
?>