Sunday, June 03, 2007

Ruby vs. JRuby - The path to consistent behavior + OpenSSL

In Ola Bini's recent post There can be only one, a tale about Ruby, IronRuby, MS and whatnot, he stresses the importance of documenting Ruby's API so that other implementations can match MRI's behavior. I have to strongly agree. We've recently been bitten by this, which I'll outline using OpenSSL as an example.

Ruby's OpenSSL library does not strictly enforce a ciphers's initialization vector (IV) size specification. It simply truncates to the appropriate size.

Ola's JRuby OpenSSL library (which is awesome btw!) leverages the Bouncy Castle's JCE implementation which strictly enforces IV specifications.

Below is a simple example that works fine on MRI, and fails on JRuby.

require 'openssl'
text = "abc123"
cipher ="des-ecb")

#The DES Cipher specifies a length of 8 bytes, the below IV exceeds that
key, iv = "1234567890", "1234567890"

cipher.key, cipher.iv = key, iv
encrypted = cipher.update(text) <<


#I double the length of the cipher here, just to prove that MRI truncates it.
cipher.key, cipher.iv = key*2, iv*2
decrypted = cipher.update(encrypted) <<
puts "#{text} == #{decrypted}"

> jruby test_openssl_iv.rb DES key too long - should be 8 bytes
at org.bouncycastle.jce.provider.JCEBlockCipher.engineInit(Unknown Source)
at org.bouncycastle.jce.provider.JCEBlockCipher.engineInit(Unknown Source)
at javax.crypto.Cipher.init(DashoA12275)
at javax.crypto.Cipher.init(DashoA12275)
at org.jruby.ext.openssl.Cipher.doInitialize(
at org.jruby.ext.openssl.Cipher.update(

> ruby test_openssl_iv.rb 
Result is: abc123 == abc123

Yes, this is obviously an edge case, and one could argue that the Java implementation is more correct than MRI's, but the goal is any piece of code should run the same on either platform.

Charles Nutter (Headius) has started a RubySpec Wiki where I've noted this issue there.

I've submitted a bug against JRuby to track the issue, but arguably its not a JRuby bug. Its a difference between BouncyCastle and SSLeay's implementation. I'd be interested in some community feedback on how to correctly implement this. For now, we've worked around this by simply truncating if the RUBY_PLATFORM =~ /java/, which I know if horrible, but it allows me to move on.

1 comment:

Anonymous said...

D:\>jruby try.rb
abc123 == abc123

D:\>ruby try.rb
abc123 == abc123

Now I got the same result with JRuby 1.1.6.