php：如何为同一个字符串生成不同的输出

Question

Is there some way to generate different output for same given string, here is example:

echo md5('test');

That always generates same fb469d7ef430b0baf0cab6c436e70375 for the given input. How do I generate different encrypted text each time and be able to decrypt it later if needed ?

I have seen functions such as md5, base64_encode, crypt, sha1, etc but they generate same output and secondly I cannot decrypt later if needed.

P.S: I know I can go with one way encryption and compare encrypted texts but for a particular scenario, I have requirement to be able to decrypt text completely if needed later however I am not able to figure out if there is some way or function in php for it.

Any help will be greatly appreciated. Thanks

Answer 1

To encrypt the same plaintext so that it generates different ciphertext you change the key (and/or Initialization Vector (IV) depending on the mode of the algorithm, like CBC).

Example:

$string = 'Some Secret thing I want to encrypt'; 
$iv = '12345678'; 
$passphrase = '8chrsLng'; 

$encryptedString = encryptString($string, $passphrase, $iv); 
// Expect: 7DjnpOXG+FrUaOuc8x6vyrkk3atSiAf425ly5KpG7lOYgwouw2UATw== 

function encryptString($unencryptedText, $passphrase, $iv) { 
  $enc = mcrypt_encrypt(MCRYPT_BLOWFISH, $passphrase, $unencryptedText, MCRYPT_MODE_CBC, $iv); 
  return base64_encode($enc); 
}

Both the same IV and the passphrase must be used when decrypting in CBC mode. The passphrase MUST be kept a secret (from eavesdroppers) while the IV can be transmitted in the clear.

You CAN (but should not) use the same passphrase for every message/data but you should ALWAYS change the IV for each message/data.

This is the basics of encryption but depending on you needs you may need to modify your architecture to keep the system secure.