Description:
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openssl_decrypt fails to decrypt the result from openssl_encrypt for GCM based authenticated encryption methods supported in openssl like 'aes-128-gcm'.

The below example works for aes-128-cbc and other cipher methods, but not 'aes-128-gcm','aes-192-gcm','aes-256-gcm', despite all of those being listed as supported in openssl_get_cipher_methods().

The reason it fails, is because openssl_encrypt does not insert the "authenticated encryption tag" into the encrypted string.

This affects PHP 5.6, 7.0, 7.1.0RC5.


Test script:
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<?php
$methods = openssl_get_cipher_methods();
$method='aes-128-gcm';
//$method='aes-128-cbc';

$data = 'junk data';
$key = openssl_random_pseudo_bytes(16);
$iv = openssl_random_pseudo_bytes(openssl_cipher_iv_length($method));
$encrypted = openssl_encrypt($data, $method, $key, $options=0, $iv);
$decrypted = openssl_decrypt($encrypted, $method, $key, $options=0, $iv);
echo $data."\n";
echo $encrypted."\n";
echo $decrypted."\n";


Expected result:
----------------
junk data
iu8Ijn2SndGXJll4qpxLWL0rsEsTiNoAMw==
junk data


Actual result:
--------------
junk data
iu8Ijn2SndGX