How can I mcrypt 128 CFB to Ruby? - php

Question

I need to exchange with a PHP API which crypts the requests and answers. On my side I am in rails 4.0.0 (ruby 2.0) and I cannot make it work.
I have read a lot of answers on this subject and have tried to understand how mcrypt works, e.g. http://www.chilkatsoft.com/p/php_aes.asp, but without success. I still cannot decrypt the encrypted from PHP or encrypt something that the PHP can decrypt
Could you help me please and see what I am doing wrong?
PHP code:
$secretKey = "1234567891234567";
$encrypt = urlencode( base64_encode( mcrypt_encrypt(
MCRYPT_RIJNDAEL_128,
md5($secretKey),
$cleartext,
MCRYPT_MODE_CFB,
$secretKey
) ) );
$input = urldecode($input);
$decrypt = mcrypt_decrypt( MCRYPT_RIJNDAEL_128,
md5($secretKey),
base64_decode($input),
MCRYPT_MODE_CFB,
$secretKey );
Ruby code:
def self.encode(params = {})
cipher = OpenSSL::Cipher::AES.new(256, :CFB)
cipher.encrypt
cipher.key = Digest::MD5.hexdigest("1234567891234567")
cipher.iv = "1234567891234567"
encrypted = cipher.update(params.to_query) + cipher.final
CGI.escape(Base64.strict_encode64(encrypted))
end
def self.decode(answer)
decrypted = Base64.decode64(CGI.unescape(answer))
decipher = OpenSSL::Cipher::AES.new(256, :CFB)
decipher.decrypt
decipher.key = Digest::MD5.hexdigest("1234567891234567")
decipher.iv = "1234567891234567"
decoded = decipher.update(decrypted) + decipher.final
end

Answer 1

You have to use 'ncfb' instead of MCRYPT_MODE_CFB in the PHP code. PHP defaults to an 8 bit feed back instead of a feed back of the full block size.
Alternatively you can specify :CFB8 to be compatible with PHP in Ruby. This one I guessed after reading the documentation for CFB in the OpenSSL documentation.
Many thanks to this Q/A on IT security which I only found because I knew what I was looking for.

Answer 2

take a look at https://github.com/kingpong/ruby-mcrypt
in your gem file add
gem "ruby-mcrypt", :lib => "mcrypt"
Usage
crypto = Mcrypt.new(:twofish, :cbc, MY_KEY, MY_IV, :pkcs)
# encryption and decryption in one step
ciphertext = crypto.encrypt(plaintext)
plaintext = crypto.decrypt(ciphertext)
# encrypt in smaller steps
while chunk = $stdin.read(4096)
$stdout << crypto.encrypt_more(chunk)
end
$stdout << crypto.encrypt_finish
# or decrypt:
while chunk = $stdin.read(4096)
$stdout << crypto.decrypt_more(chunk)
end
$stdout << crypto.decrypt_finish
you can also check out https://stackoverflow.com/a/21489711/1380867