Decrypt Data in Ruby using OpenSSL

Question

I have the following code in Python that works well. It decrypts the data in the variable encrypted_data using the mcrypt module. I want to perform the same operations in Ruby. Therefore I required the openssl module. Unfortunately the Ruby version does not work. This is the error:

`final': bad decrypt (OpenSSL::Cipher::CipherError)

EDIT I created a GitHub repository for you to test this. Download the sourcecode here: github.com/ph3nx/ruby-decrypt

EDIT 2 The bad decrypt error does not appear anymore. I fixed this by setting d.padding = 0. Problem is: the decrypted data is still not correct. I can't view the image.

If you need additional Information about my system or anything else feel free to ask. Any help is highly appreciated. Thanks!

Python

import base64
import mcrypt

encrypted_data = "placeholder: This is the encrypted data."

key = base64.b64decode("6vYJkO5beHNlwOm+aMqUTTzSpRw9jR3faHqu0wVoAG0=")
iv = base64.b64decode("EbuuKuVF4+DzDbWsvQi/ZA==")

m = mcrypt.MCRYPT("rijndael-128", "cbc")
m.init(key, iv)
decrypted_data = m.decrypt(encrypted_data)

Ruby

require 'base64'
require 'openssl'

encrypted_data = "placeholder: This is the encrypted data."

key = Base64.decode64("6vYJkO5beHNlwOm+aMqUTTzSpRw9jR3faHqu0wVoAG0=")
iv = Base64.decode64("EbuuKuVF4+DzDbWsvQi/ZA==")

d = OpenSSL::Cipher::AES128.new :CBC
d.decrypt
d.padding = 0
d.key = key
d.iv = iv
decrypted_data = d.update(encrypted_data) << d.final

Decryption is not decoding. Ciphertext contains random bytes so it should not be converted directly to/from a string. — Maarten Bodewes
– Maarten Bodewes, Commented Mar 7, 2014 at 2:30
@owlstead Yes, you are right! The program derypts data. I changed the code accordingly. — ph3nx
– ph3nx, Commented Mar 7, 2014 at 9:24
@tsundoku The data is loaded from a different server. I don't know which programming language is used to encrypt the data. Why is this important? — ph3nx
– ph3nx, Commented Mar 7, 2014 at 9:26
There are a couple of settings to tweak, e.g. if you set d.padding = 0, from here: stackoverflow.com/questions/19661508/… — tsundoku
– tsundoku, Commented Mar 7, 2014 at 9:31

bbozo · Accepted Answer · 2014-03-14 07:50:30Z

1

+50

I have found OpenSSL integration to be lacking in Ruby, and generally more cumbersome (uglier api / less convention over configuration) for cryptographic work then mcrypt.

If you're using mcrypt in python successfully, why not use mcrypt in ruby too? https://github.com/kingpong/ruby-mcrypt

Something in the lines of:

require 'rubygems'
require 'mcrypt'
crypto = Mcrypt.new("rijndael-128", :cbc, key, iv)
decrypted_data = crypto.decrypt(encrypted_data)

should work in your case.

I can extend on this answer later today or tomorrow, got some traveling to do first

edited Mar 14, 2014 at 7:50

answered Mar 14, 2014 at 5:45

bbozo

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2 Comments

ph3nx Over a year ago

You're a genius! This works exactly how I wanted. Do you know if there are differences in performance between mcrypt and openssl?

bbozo Over a year ago

Lol thank you :) I'm glad it helped :) I don't know about performance differences, but they're all C-binded libs so mcrypt performance should be pretty good. We used ruby-mcrypt for encrypting some 10 million records or so in a live system with 700k users and we didn't run into any bottlenecks in performance there

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