Edit report at https://bugs.php.net/bug.php?id=67304&edit=1
ID: 67304
Comment by: albertcasademont at gmail dot com
Reported by: birki456 at hotmail dot com
Summary: openssl_decrypt fails with GCM mode
Status: Open
Type: Feature/Change Request
Package: OpenSSL related
Operating System: all
PHP Version: 5.5.12
Block user comment: N
Private report: N
New Comment:
This would be indeed very useful. Right now we have to do it in 2 steps with an hmac
Previous Comments:
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[2014-05-19 17:00:18] birki456 at hotmail dot com
Description:
------------
While the gcm mode (which is authenticated encryption) is reported in openssl_get_cipher_methods()
(e.g. [106] => aes-256-gcm), neither openssl_encrypt nor openssl_decrypt support it. There simply
is no code to supply/return the authentication tag. It should be fairly simple to add however it
possibly requires a change of the return type, because ciphertext and tag need to be returned in the
encryption case and ciphertext and tag need to be supplied for decryption. It should also be
possible to distinguish between decryption failure due to authentication failure vs. other failure.
The code below *should*, as last line, print 'recovered: Hello World', however decryption
with gcm always fails.
Test script:
---------------
echo print_r(openssl_get_cipher_methods(), true);
$cipher = 'aes-256-gcm';
$ivlen = openssl_cipher_iv_length($cipher);
echo "iv len: " . $ivlen . "\n";
$iv = openssl_random_pseudo_bytes($ivlen);
$hexiv = bin2hex($iv);
echo "iv: " . $hexiv . "\n";
$plaintext = "Hello World";
echo "plaintext: " . $plaintext . "\n";
$clearpass = 'passphrase';
$pbkdfsalt = openssl_random_pseudo_bytes(16);
$password = hash_pbkdf2('sha256', $clearpass, $pbkdfsalt, 1001, 32, true);
echo "clearpass: " . $clearpass . "\n";
echo "pbkdfsalt: " . bin2hex($pbkdfsalt) . "\n";
echo "password: " . bin2hex($password) . "\n";
// This is the important part:
$ciphertext = openssl_encrypt($plaintext, $cipher, $password, 0, $iv);
echo "ciphertext: " . print_r($ciphertext, true) . "\n";
$recovered = openssl_decrypt($ciphertext, $cipher, $password, 0, $iv);
echo "recovered: " . $recovered . "\n";
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Edit this bug report at https://bugs.php.net/bug.php?id=67304&edit=1