Question

I’m rewriting some existing code from Python to Ruby, and I’ve across a strange error that I can’t seem to figure out. Here we have the Python code (which works):

import sha, hmac
data = 'sampledata'
data = data.encode('ascii')
des_key = hmac.new(data + "\0", "SUPERSECRET", sha).digest()[0:8]

Output: 0x64F461D377D9930C

And the Ruby (which I’m new to) code:

require 'openssl'
digest  = OpenSSL::Digest::SHA.new
data = 'sampledata'
data.encode!('ascii')
puts OpenSSL::HMAC.hexdigest(digest, "SUPERSECRET", data + "\0")[0, 16]

Output: 0x563FDAF11E63277C

What could be causing this difference?

Answer 1

You made two mistakes:

1. Python’s hmac.new takes key, method, digest – so you should write

   hmac.new(“SUPERSECRET”,data + “\0”, sha)

2. The default digest method for OpenSSL::Digest in Ruby isn’t SHA1 (I’m not sure what it is). You should just use:

   OpenSSL::HMAC.hexdigest(‘sha1’,”SUPERSECRET”,data+”\0″)[0,16]

Both methods (first in Python, second in Ruby) return the same output.