Ruby HMAC-SHA Differs from Python

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?

Guy Adini · Accepted Answer · 2012-07-22 09:23:58Z

5

You made two mistakes:

Python's hmac.new takes key, method, digest - so you should write

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

answered Jul 22, 2012 at 9:23

Guy Adini

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Comments

steenslag · Accepted Answer · 2012-07-22 18:53:11Z

4

In addition to Guy Adini's answer - in Ruby SHA is different from python sha which is sha1 (in sha.py: from hashlib import sha1 as sha):

from hashlib import *
import hmac
data = 'sampledata'
data = data.encode('ascii')

algo = [sha1, sha224, sha256, sha512]
for al in algo:
    print al().name, hmac.new("SUPERSECRET", data + "\0", al).hexdigest()[0:16]

produces:

sha1 50c61ea49195f03c
sha224 fd6a418ee0ae21c8
sha256 79deab13bd7b041a
sha512 31561f9c9df69ab2

and in Ruby:

require 'openssl'
data = 'sampledata'
data.encode!('ascii')
%w(sha sha1 sha224 sha256 sha512).each do |al|
  puts "#{al}: #{OpenSSL::HMAC::hexdigest(al, "SUPERSECRET", "#{data}\0")[0,16]}"
end

produces:

sha: 563fdaf11e63277c
sha1: 50c61ea49195f03c
sha224: fd6a418ee0ae21c8
sha256: 79deab13bd7b041a
sha512: 31561f9c9df69ab2

edited Jul 22, 2012 at 18:53

steenslag

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answered Jul 22, 2012 at 9:38

Tisho

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5 Comments

Guy Adini Over a year ago

Cool - so which version of SHA is ruby's default SHA algorithm? And which one is python's? The default version in Python didn't return the same value as the sha1 algorithm.

Tisho Over a year ago

The default digest in Python is md5(if no digest is specified in new() function).

Guy Adini Over a year ago

Thanks - but I mean, when Lander wrote des_key = hmac.new(data + "\0", "SUPERSECRET", sha).digest()[0:8], he got a result which didn't match any of al in algo... So which sha did he get (not md5, I guess).

Tisho Over a year ago

Not quite sure, but the 'SHA' in Ruby seems to be 'SHA0', which is deprecated in Python from a long time, as it is easy to crack...

Lander Over a year ago

Thank you for the info! That's a very nice representation, and since I'm new to Ruby I learned an easy way to write word arrays.

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