5

I have an encrypted bit of text that I need to decrypt. It's encrypted with AES-256-CBC. I have the encrypted text, key, and iv. However, no matter what I try I just can't seem to get it to work.

The internet has suggested that mcrypt's Rijndael cypher should be able to do this, so here's what I have now:

function decrypt_data($data, $iv, $key) { $cypher = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '', MCRYPT_MODE_CBC, ''); // initialize encryption handle if (mcrypt_generic_init($cypher, $key, $iv) != -1) { // decrypt $decrypted = mdecrypt_generic($cypher, $data); // clean up mcrypt_generic_deinit($cypher); mcrypt_module_close($cypher); return $decrypted; } return false; }

As it stands now I get 2 warnings and the output is gibberish:

Warning: mcrypt_generic_init() [function.mcrypt-generic-init]: Key size too large; supplied length: 64, max: 32 in /var/www/includes/function.decrypt_data.php on line 8 Warning: mcrypt_generic_init() [function.mcrypt-generic-init]: Iv size incorrect; supplied length: 32, needed: 16 in /var/www/includes/function.decrypt_data.php on line 8

Any help would be appreciated.

Improve this question

2 Answers 2

Reset to default
6

I'm not terribly familiar with this stuff, but it seems like trying MCRYPT_RIJNDAEL_256 in place of MCRYPT_RIJNDAEL_128 would be an obvious next step...

Edit: You're right -- this isn't what you need. MCRYPT_RIJNDAEL_128 is in fact the right choice. According to the link you provided, your key and IV are twice as long as they should be:

// How do you do 256-bit AES encryption in PHP vs. 128-bit AES encryption??? // The answer is: Give it a key that's 32 bytes long as opposed to 16 bytes long. // For example: $key256 = '12345678901234561234567890123456'; $key128 = '1234567890123456'; // Here's our 128-bit IV which is used for both 256-bit and 128-bit keys. $iv = '1234567890123456';
Improve this answer
Sign up to request clarification or add additional context in comments.

5 Comments

Yeah, I tried it. According to chilkatsoft.com/p/php_aes.asp that is the block size, not the key size.
Good catch. The link you provided has the answer to your question: You have to provide a 32 byte key, and a 16 byte IV. You're passing in values that are twice as long as they need to be.
It turns out the were hex encoded and just needed to be run through pack('H*', $var).
Sorry for sounding dumb, but what exactly do you pack() ? Ive been trying to do this myself, without any luck..
@NilsMunch You use pack() to convert the Hex representation to the actual binary 128/256 bit representation.
1

I send to you one example, Please, check the code, ok

$data_to_encrypt = "2~1~000024~0910~20130723092446~T~00002000~USD~F~375019001012120~0~0~00000000000~"; $key128 = "abcdef0123456789abcdef0123456789"; $iv = "0000000000000000"; $cc = $data_to_encrypt; $key = $key128; $iv = $iv; $length = strlen($cc); $cipher = mcrypt_module_open(MCRYPT_RIJNDAEL_128,'','cbc',''); mcrypt_generic_init($cipher, $key, $iv); $encrypted = base64_encode(mcrypt_generic($cipher,$cc)); mcrypt_generic_deinit($cipher); mcrypt_generic_init($cipher, $key, $iv); $decrypted = mdecrypt_generic($cipher,base64_decode($encrypted)); mcrypt_generic_deinit($cipher); echo "encrypted: " . $encrypted; echo "<br/>"; echo "length:".strlen($encrypted); echo "<br/>"; echo "decrypted: " . substr($decrypted, 0, $length);
Improve this answer

1 Comment

Worked for me! The only suggestion I have is to use rtrim instead of substr for the decrypted text since you may not always know the length. rtrim($decrypted, "\0")

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.