iteration-guesser.rb

#!/usr/bin/env ruby

require 'openssl'

SHA1 = OpenSSL::Digest::SHA1.new

# Verified functionality against
# Test Vector (http://tools.ietf.org/html/draft-josefsson-pbkdf2-test-vectors-06#page-3)
#      Input:
#       P = "password" (8 octets)
#       S = "salt" (4 octets)
#       c = 4096
#       dkLen = 20
#
#     Output:
#       DK = 4b 00 79 01 b7 65 48 9a
#            be ad 49 d9 26 f7 21 d0
#            65 a4 29 c1             (20 octets)

# With a known salt and password and derived key, we can brute force the
# number of iterations it took to derive the key.
def bf_iteration(salt, password, derived_key, pbkdf2_dKeyLen)
	(1..65536).each do |i|
		try_iteration(salt, password, derived_key, pbkdf2_dKeyLen, i)
	end
	puts "Sorry, number of iterations not found"
end

def try_iteration(salt, password, hash, pbkdf2_dKeyLen, pbkdf2_num_iterations)
		dk = OpenSSL::PKCS5.pbkdf2_hmac_sha1(password, salt, pbkdf2_num_iterations, pbkdf2_dKeyLen)
		if dk == hash
			puts "!!! Found, form of PBKDF2(salt, password, dKLen:#{pbkdf2_dKeyLen}, Iterations:#{pbkdf2_num_iterations})"
			puts "input hash:#{hash.unpack('H*')[0]} generated hash:#{dk.unpack('H*')[0]}"
			exit
		elsif ((hash.length == 20) and (SHA1.digest(dk) == hash))
			puts "!!! Found, form of SHA1(PBKDF2(salt, password, dKlen:#{pbkdf2_dKeyLen}, Iterations:#{pbkdf2_num_iterations}))"
			puts "input hash:#{hash.unpack('H*')[0]} generated hash:#{SHA1.digest(dk).unpack('H*')[0]}"
			exit
		end
end

if ARGV.length != 3
	puts "Usage: #{$0} password salt hash\n"
	puts "Password: The password"
	puts "Salt: salt bytes as a hex string"
	puts "Hash: hash bytes as a hex string"
	exit
end
password = ARGV[0]
salt_hex = ARGV[1]
hash_hex = ARGV[2]
unless ((salt_hex =~ /[0-9a-zA-z]/) and ((salt_hex.length % 2) == 0))
	puts "Error: Invalid salt, try again"
	exit
end
unless ((hash_hex =~ /[0-9a-zA-z]/) and ((hash_hex.length % 2) == 0))
	puts "Error: Invalid key, try again"
	exit
end

salt = [salt_hex].pack('H*')
hash = [hash_hex].pack('H*')
#bf_iteration(salt, password, hash, 20)
#[20, 24].each do |dklen|
(1..1024).each do |dklen|
	puts "12,345 iterations: trying with derived key length of #{dklen}(#{dklen*8}bits)"
	try_iteration(salt, password, hash, dklen, 12345)
end