lib/password.rb

require 'digest/sha2'

# This module contains functions for hashing and storing passwords
module Password

  # Generates a new salt and rehashes the password
  def Password.update(password)
    salt = self.salt
    hash = self.hash(password,salt)
    self.store(hash, salt)
  end

  # Checks the password against the stored password
  def Password.check(password, store)
    hash = self.get_hash(store)
    salt = self.get_salt(store)
    if self.hash(password,salt) == hash
      true

    else
      false
    end
  end

  protected

  # Generates a psuedo-random 64 character string

  def Password.salt
    salt = ""
    64.times { salt << (i = Kernel.rand(62); i += ((i < 10) ? 48 : ((i < 36) ? 55 : 61 ))).chr }
    salt
  end

  # Generates a 128 character hash
  def Password.hash(password,salt)
    Digest::SHA512.hexdigest("#{password}:#{salt}")
  end

  # Mixes the hash and salt together for storage
  def Password.store(hash, salt)
    hash + salt
  end

  # Gets the hash from a stored password
  def Password.get_hash(store)
    store[0..127]
  end

  # Gets the salt from a stored password
  def Password.get_salt(store)
    store[128..192]
  end
end