gistfile1.rb

require 'digest/sha2'
require 'active_support/secure_random'

class User < ActiveRecord::Base
	validates_presence_of :username, :password, :salt
	
	def password=(pw)
		set_salt unless salt
		write_attribute :password, hash(pw)
	end
	
	def salt=(h)
		raise 'User#salt is readonly'
	end
	
	def test_password(pw)
		password == hash(pw)
	end
	
private
	def set_salt
		write_attribute :salt, SecureRandom.base64(4)
	end
	
	def hash(msg)
		digest = Digest::SHA2.new 512
		digest << salt << msg << salt
		digest.to_s
	end
end