#!/usr/bin/ruby

require 'digest'

# Copyright (c) 2009 Noa Resare (noa@voxbiblia.com)
# This code is licensed using the GPLv3 license.
class PasswordHasher

	# Converts a plaintext password into hashed form suitable for persistent
    # storage.
	def PasswordHasher.hash(plaintext)
		d = Digest::SHA1.new
		salt = get_random_bytes(4)
		d << salt
		d << plaintext
		result = "\001"
		result << salt
		result << ITERATIONS / 128
		result << iterate_sha1(d.digest!, ITERATIONS)
		return [result].pack('m')[0..-2]
	end

	# Verifies that the plaintext password matches the supplied password hash created
	# with the PasswordHasher.hash method
	def PasswordHasher.verify(plaintext, hash)
		hash = hash.unpack('m')[0]
		if hash[0] != 1
			fail "unknown hash format, doesn't start with \\001"		
		end
		d = Digest::SHA1.new
		d << hash[1..4]
		d << plaintext
		s = iterate_sha1(d.digest!, hash[5] * 128)
		return s == hash[6..-1]
	end

	private

	# number of SHA-1 iterations. Need to be a multiple of 128
	ITERATIONS = 1024

	def PasswordHasher.get_random_bytes(count)
		bytes = []
		count.times {
			bytes << rand(0xff)
		}
		return bytes.pack('C*')
	end

	def PasswordHasher.iterate_sha1(input, iterations)
		d = Digest::SHA1.new
		iterations.times {
			d << input
			input = d.digest!()
		}
		return input
	end
end