Cannot decrypt openssl_encrypt() output on command line

Question

I've written a small class for symmetric encryption with openssl, and it encrypts and decrypts fine within PHP, but I cannot seem to either decrypt the output using the command line, or encrypt the same data in the same way.

My class is:

Class SimpleCrypt {

    public static function encrypt($password, $data, $enc_method='AES-256-CBC', $hash_method='SHA512') {
        self::check_methods($enc_method, $hash_method);
        $iv = self::hashIV($password, $hash_method, openssl_cipher_iv_length($enc_method));
        $infostr = sprintf('$%s$%s$', $enc_method, $hash_method);
        return $infostr . openssl_encrypt($data, $enc_method, $password, false, $iv);
    }

    public static function decrypt($password, $edata) {
        $e_arr = explode('$', $edata);
        if( count($e_arr) != 4 ) {
            Throw new Exception('Given data is missing crucial sections.');
        }
        $enc_method = $e_arr[1];
        $hash_method = $e_arr[2];
        self::check_methods($enc_method, $hash_method);
        $iv = self::hashIV($password, $hash_method, openssl_cipher_iv_length($enc_method));
        return openssl_decrypt($e_arr[3], $enc_method, $password, false, $iv);
    }

    private static function hashIV($password, $method, $iv_size) {
        $myhash = hash($method, $password, TRUE);
        while( strlen($myhash) < $iv_size ) {
            $myhash .= hash($method, $myhash, TRUE);
        }
        return substr($myhash, 0, $iv_size);
    }

    private static function check_methods($enc, $hash) {
        if( ! function_exists('openssl_encrypt') ) {
            Throw new Exception('openssl_encrypt() not supported.');
        } else if( ! in_array($enc, openssl_get_cipher_methods()) ) {
            Throw new Exception('Encryption method ' . $enc . ' not supported.');
        } else if( ! in_array(strtolower($hash), hash_algos()) ) {
            Throw new Exception('Hashing method ' . $hash . ' not supported.');
        }
    }

} // -- end class SimpleCrypt -- //


$enc = SimpleCrypt::encrypt('pass', 'test data');
$dec = SimpleCrypt::decrypt('pass', $enc);
echo $enc . "\n" . $dec;
// Output:
// $AES-256-CBC$SHA512$yH0uN95Vya0pTwcoJRFb+g==
// test data

This bit of code reproduces the IV:

php -r 'echo strtoupper(bin2hex(substr(hash("SHA512", "pass", true), 0, openssl_cipher_iv_length("AES-256-CBC"))));'
//output: 5B722B307FCE6C944905D132691D5E4A

But this code gives me garbled otuput that doesn't resemble the input:

$ echo yH0uN95Vya0pTwcoJRFb+g== | base64 -d | openssl enc -AES-256-CBC -d -nosalt -nopad -k pass -iv 5B722B307FCE6C944905D132691D5E4A
ã`ÈAgè}½5øÍÝEÞ
00000000  e3 60 c8 41 67 e8 7d bd  35 00 f8 cd dd 45 13 de  |.`.Ag.}.5....E..|

Encoding the data from the command line gives me:

$ echo "test data" | openssl enc -e -AES-256-CBC -nosalt -k pass -iv 5B722B307FCE6C944905D132691D5E4A | hexdump -C
00000000  ca fc 84 6a 95 51 8f 0e  61 14 96 77 4e 22 dd 39  |...j.Q..a..wN".9|

$ echo "test data" | openssl enc -e -AES-256-CBC -nosalt -k pass -iv 5B722B307FCE6C944905D132691D5E4A | base64
yvyEapVRjw5hFJZ3TiLdOQ==

Can anyone tell me what I've done incorrectly in my PHP code?

Solution

Just to recap the solution from the Daniel's answer, we need to use the -K argument to openssl rather than -k or -pass and it expects a hex representation of the string. eg:

echo strtoupper(bin2hex('pass'));
//output: 70617373

And then the proper command is:

echo yH0uN95Vya0pTwcoJRFb+g== | base64 -d | openssl enc -AES-256-CBC -d -nosalt -K 70617373 -iv 5B722B307FCE6C944905D132691D5E4A | hexdump -C
00000000  74 65 73 74 20 64 61 74  61                       |test data|

Daniel Roethlisberger · Accepted Answer · 2013-02-23 20:12:12Z

1

The badly named password argument to PHP's openssl_encrypt() is not a password, it is the actual key. When using command line openssl enc with lower-case -k, OpenSSL will derive a key from the password using a key derivation function. You want to use openssl enc with upper-case -K and a hexadecimal representation of the key; and make sure to hand openssl_encrypt() a long enough key in the password argument.

See also the very first user-contributed note in the PHP manual on openssl_encrypt().

answered Feb 23, 2013 at 20:12

Daniel Roethlisberger

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