current_decryption.rb

require 'openssl'
require 'base64'

key = '7fc4d85e2e4193b8'

crypted_text = Base64.decode64(ARGV[0])

cipher = OpenSSL::Cipher::Cipher.new("aes-128-cbc")
cipher.decrypt
cipher.key = key

decrypted = ""
decrypted << cipher.update(crypted_text)
decrypted << cipher.final

current_encryption.php

<?php
$key = "7fc4d85e2e4193b8";
$text = "Read me! This is a fun message...";
$iv = "OpenSSL for Ruby";

// Add required padding
$pad = 16 - (strlen($crypttext) % 16);
$text = $text . str_repeat(chr($pad), $pad);

// XOR first block due to ruby's openssl performing this when using the static IV
for ($i = 0; $i < 16; $i++) {
  $text[$i] = $text[$i] ^ $iv[$i];
}

$encrypted = base64_encode(mcrypt_encrypt(MCRYPT_RIJNDAEL_128, $key, $text, MCRYPT_MODE_CBC, $iv));

print $encrypted ."\n";
?>

proposed_decryption.rb

require 'openssl'
require 'base64'

key = '7fc4d85e2e4193b8'

crypted_text = Base64.decode64(ARGV[0])
iv = "Random IV Winner"

cipher = OpenSSL::Cipher::Cipher.new("aes-128-cbc")
cipher.decrypt
cipher.key = key
cipher.iv = "OpenSSL NOT Ruby"

decrypted = ""
decrypted << cipher.update(crypted_text)
decrypted << cipher.final

proposed_encryption.php

<?php
$key = "7fc4d85e2e4193b8";
$text = "Read me! This is a fun message...";
$iv = "Random IV Winner";

// Add required padding
$pad = 16 - (strlen($crypttext) % 16);
$text = $text . str_repeat(chr($pad), $pad);

$encrypted = base64_encode(mcrypt_encrypt(MCRYPT_RIJNDAEL_128, $key, $text, MCRYPT_MODE_CBC, $iv));

print $encrypted ."\n";
?>