Blum Blum Shub Pseudo Random Number Generator

blumblumshub.coffee

# An implementation of assert.
AssertException = (message) ->
  @message = message
assert = (exp, message) ->
  throw new AssertException(message)  unless exp
AssertException::toString = ->
  "AssertException: " + @message



# Implementation of Blum Blum Shub 
# p - Large Prime 1. Should be congruent to 3 mod 4.
# q - Large Prime 2. Should be to congruent to 3 mod 4.
# s - The seed. Should be a co-prime of the product of p and q.

blum_blum_shub = (p,q,s,i) ->
  # Primes p and q must be congruent to 3 mod 4
  assert((p % 4) == 3, "Error: Prime P is not congruent to 3 mod 4")
  assert((q % 4) == 3, "Error: Prime Q is not congruent to 3 mod 4")

  m = p * q
  
  x = s

  for step in [0..i]
    x = (x * x) % m
  
  x