Data encrypted with phpseclib cannot be decrypted using openssl - php

Question

I am using phpseclib to encode the contents of a json file using a random key as follows:
$plainkey = openssl_random_pseudo_bytes(32);
$iv = openssl_random_pseudo_bytes(16);
$payload_plain = file_get_contents("file.json");
$cipher = new Crypt_AES(CRYPT_AES_MODE_CBC);
$cipher->setKeyLength(256);
$cipher->setKey($plainkey);
$cipher->setIV($iv);
$enc_payload = $cipher->encrypt($payload_plain);
At this point, $enc_payload contains the ciphertext, and calling $cipher->decode on it returns the plaintext, as expected. So far so good.
The problem arises when i write this encrypted data to a file and then try to decrypt it using openssl, using a command such as the one below:
openssl enc -d -aes-256-cbc -iv 17741abad138acc10ab340aaa7c4b790 -K d96ab4a30d73313d4c525844fce61d9f925e119cf178761b27ad0deab92a32bf -in encrypted.txt -out plain.txt
whereby the values for -iv and -K have been obtained by using bin2hex on the random byte values obtained in the script above.
Running that command gives me an error and plain.txt contains a half correct / half scrambled version of the original json string.
Error:
bad decrypt
13124:error:0606506D:digital envelope routines:EVP_DecryptFinal_ex:wrong final block length:.\crypto\evp\evp_enc.c:323:
What am i missing? I am thinking maybe the part where i use bin2hex on the key / iv is incorrect, but I have tried using the byte strings directly without any success. How is this done normally? Or am i missing anything obvious?
Thanks

Answer 1

It worked fine for me. My code (adapted from yours):
<?php
include('Crypt/AES.php');
$plainkey = pack('H*', 'd96ab4a30d73313d4c525844fce61d9f925e119cf178761b27ad0deab92a32bf');
$iv = pack('H*', '17741abad138acc10ab340aaa7c4b790');
$payload_plain = file_get_contents('plaintext.txt');
$cipher = new Crypt_AES(CRYPT_AES_MODE_CBC);
$cipher->setKeyLength(256);
$cipher->setKey($plainkey);
$cipher->setIV($iv);
$enc_payload = $cipher->encrypt($payload_plain);
file_put_contents('ciphertext.txt', $enc_payload);
I decrypted with this:
openssl enc -d -aes-256-cbc -iv 17741abad138acc10ab340aaa7c4b790 -K d96ab4a30d73313d4c525844fce61d9f925e119cf178761b27ad0deab92a32bf -nosalt -p -in encrypted.txt -out plaintext.txt
The difference is that I have -p and -nosalt. -p just prints the keys out but maybe -nosalt is what you need.
Or maybe the problem is simpler than even this. In the code snippet you posted you're not echo'ing or saving the key / iv anywhere. Maybe you're not outputting the right values.
I got the OpenSSL parameters from http://phpseclib.sourceforge.net/interop.html#aes,p1openssl,p2phpseclib