php openssl的到期时间？

Question

I'm not very familiar with encryption, and we are now using PHP's openssl_encrypt/decrypt in our application.

Is it possible to make the encryption/decryption work only before an expiry time? e.g. maybe the keys expire?

Answer 1

Yes, it is possible, you have to append the creation timestamp as bytes before what you need to encrypt:

$time = pack('N', time());
$enc = openssl_encrypt($time . $other_data, ...);

When you decrypt:

$dec = openssl_decrypt($encrypted, ...);
$time = unpack('N', substr($dec, 0, 4));
$other_data = substr($dec, 4);
if (time() - $time[1] > $EXPIRY_SECONDS)
   die('Expired');

The N flag i've used in pack/unpack is for Big Endian byte order, you can also use V for little endian or L for machine-dependent, because the timestamp fit in 32 bit integer (4 bytes).