security - AES encrypt in Terminal and decrypt in PHP

Question

I have come accross other threads with similar questions but due to recent changes in PHP (ie. mcrypt removal), I am seeking some advice as to how I'd best go about this using OpenSSL in 2017/18.

Using echo 'this string will be encrypted' | openssl enc -aes-256-cbc -a -pass pass:123 in the Mac Terminal, I was able to password encrypt the string and would now like to pass this (as a parameter) into a server-side PHP function to decrypt.

Having studied this question, I can see that it is possible but it uses the now removed mcrypt function. Further reading in the PHP manual, I am no closer to figuring out how to reverse this encryption command into its PHP decryption equivalent.

This recent answer is what I have implemented so far, yet again, it just won't work with a Terminal generated encryption, only one which was created in PHP (not shown here).

<?php
  $encrypted_string = $_GET['data'];
  $password = '123';
  $decrypted_data = openssl_decrypt($encrypted_string, "AES-256-CBC", $password);
  print "Decrypted Data: <$decrypted_data>
";
?>

The OpenSSL PHP manual states that either plain text or base64 encoded strings can be passed in and be decrypted. As I have used the -a flag during encryption, I would expect base64 to be passed in, thus eliminating the source as a potential reason why no decrypted data is returned.

I have taken care of URL encoding such that any + symbols produced by the encryption algorithm are replaced with their - %2B - URL-Safe equivalent as they would otherwise be turned into a space character, thus breaking the parameter string. This further ensures that the encoded input string is correctly addressed by the decryption algorithm.

Questions: Why won't my PHP function decrypt the string generated by the terminal command, although both use the same method and password? What is missing from my PHP code that would enable this to work?

Cheers everyone.

UPDATE

I am now using Terminal command:
echo 'blah' | openssl enc -aes-256-cbc -a -K B374A26A71490437AA024E4FADD5B497FDFF1A8EA6FF12F6FB65AF2720B59CCF -iv 64299685b2cc8da5 which encrypts to: Y4xelTtEJPUHytB5ARwUHQ==

I pass this to PHP using www.example.com/?data=Y4xelTtEJPUHytB5ARwUHQ==

PHP should take data param and decrypt. Currently, that function looks like this:

<?php
$encrypted_string = base64_decode($_GET['data']);
$key = 'B374A26A71490437AA024E4FADD5B497FDFF1A8EA6FF12F6FB65AF2720B59CCF';
$iv = '64299685b2cc8da5';

$output = openssl_decrypt($encrypted_string, 'AES-256-CBC', hex2bin($key), OPENSSL_RAW_DATA, hex2bin($iv));
print "Decrypted Data: <$output>
";
?>

Answer 1

OpenSSL uses a proprietary KDF that you probably don't want to put the effort in to reproduce in PHP code. However, you can pass your key as pure hex instead, avoiding the KDF, by using the -K flag:

echo 'blah' | openssl enc -aes-256-cbc -K 0000000000000000000000000000000000000000000000000000000000000000

Here, the large hex string is your 256-bit key, hex encoded. This encryption operation will be compatible with your PHP.