From: Anth <davidlundquist@...>
Date: 2009-09-01T21:35:05+09:00
Subject: Re: AES encryption between c# and ruby

On Sep 1, 3:00 pm, Brian Candler <b.cand...@pobox.com> wrote:
> Anth wrote:
> > Having some issues getting this to work, dont know much about
> > encryption and I think im just doing a silly misstake somewhere. Would
> > appreciate a pointer or two in the correct direction.
>
> > Encrypting "a" in c# using AES 256 bit cbc yields
>
> > RZ8NxW9+S1qfzd9VRtzV4sFuHFuXJ3mzBpjwCTzbxJQ=
>
> > Whilst in ruby I get: uNL1Ogvi+mQyWGniJRY88g==
>
> > Ruby code:http://pastie.org/601527
> > c# code:http://pastie.org/601526
>
> Observe that the first gives 32 bytes (256 bits), while the second gives
> 16 bytes (128 bits).
>
> >> "RZ8NxW9+S1qfzd9VRtzV4sFuHFuXJ3mzBpjwCTzbxJQ=".unpack("m").first.size
> => 32
> >> "uNL1Ogvi+mQyWGniJRY88g==".unpack("m").first.size
>
> => 16
>
> You should seehttp://en.wikipedia.org/wiki/Aes256
>
> "AES has a fixed block size of 128 bits and a key size of 128, 192, or
> 256 bits, whereas Rijndael can be specified with block and key sizes in
> any multiple of 32 bits, with a minimum of 128 bits and a maximum of 256
> bits."
>
> Your C# code appears to be using Rijndael, presumably with a 256 bit
> block size, whereas Openssl is using AES.
>
> Anyway, I can get the same results from both Ruby and the openssl
> command line tool, if I modify your Ruby program as follows:
>
>     cipher_enc.iv = "\x00" * 16
>     cipher_enc.key = "\x00" * 32
>     ...
>     puts output_str.unpack("H*").first
>
> $ echo -n "a" | openssl aes-256-cbc -K 0 -iv 0 | hexdump -C
> 00000000  b4 a5 e9 8a f6 81 0a 83  bd f5 2b 14 ae 82 2c 37
> |..........+...,7|
> 00000010
>
> This demonstrates you are doing AES encryption properly. But AES with a
> 256 bit key and a 128 bit block size is not the same as Rijndael with a
> 256 bit block size.
>
> You may find the AES test vectors on the Wikipedia page helpful too.
>
> HTH,
>
> Brian.
> --
> Posted viahttp://www.ruby-forum.com/.

Thanks alot for the clarification. Problem now is that I want the ruby
code to decrypt the c# code (the way the c# code works is the way the
ruby code is supposed to work) but the documentation for this is
horrid, how would I go about decrypting the string I would get from
the c# example (eg rijndael 256 bit blocksize) any idea?

Cheers
David