Class: Crypt::ISAAC

Inherits:
Object
  • Object
show all
Defined in:
lib/crypt/isaac.rb

Overview

ISAAC is a fast, strong random number generator. Details on the algorithm can be found here: burtleburtle.net/bob/rand/isaac.html This provides a consistent and capable algorithm for producing independent streams of quality random numbers.

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(seed = true) ⇒ ISAAC

When a Crypt::ISAAC object is created, it needs to be seeded for random number generation. If the system has a /dev/urandom file, that will be used to do the seeding by default. If false is explictly passed when creating the object, it will instead use /dev/random to generate its seeds. Be warned that this may make for SLOW initialization. If the requested source (/dev/urandom or /dev/random) do not exist, the system will fall back to a simplistic initialization mechanism using the builtin Mersenne Twister PRNG.



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# File 'lib/crypt/isaac.rb', line 23

def initialize(seed = true)
  @mm = []

  if Integer === seed || Random === seed
    self.srand(seed)
  else
    @seed = seed
    rnd_source = ( ( seed == true ) || ( seed == false ) ) ?
      ( seed ? '/dev/urandom' : '/dev/random' ) :
      seed
    if (FileTest.exist? rnd_source)
      @randrsl = []
      File.open(rnd_source,'r') do |r|
        256.times do |t|
          z = r.read(4)
          x = z.unpack('V')[0]
          @randrsl[t] = x
        end
      end
      randinit(true)
    else
      raise "Entropy source (#{rnd_source}) doesn't exist. The ISAAC algorithm can not be seeded."
    end
  end
end

Instance Attribute Details

#aa ⇒ Object

Returns the value of attribute aa.



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# File 'lib/crypt/isaac.rb', line 11

def aa
  @aa
end

#bb ⇒ Object

Returns the value of attribute bb.



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# File 'lib/crypt/isaac.rb', line 11

def bb
  @bb
end

#cc ⇒ Object

Returns the value of attribute cc.



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# File 'lib/crypt/isaac.rb', line 11

def cc
  @cc
end

#mm ⇒ Object

Returns the value of attribute mm.



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# File 'lib/crypt/isaac.rb', line 11

def mm
  @mm
end

#randcnt ⇒ Object

Returns the value of attribute randcnt.



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# File 'lib/crypt/isaac.rb', line 10

def randcnt
  @randcnt
end

#randrsl ⇒ Object

Returns the value of attribute randrsl.



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# File 'lib/crypt/isaac.rb', line 10

def randrsl
  @randrsl
end

Instance Method Details

#==(gen) ⇒ Object 



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# File 'lib/crypt/isaac.rb', line 93

def ==(gen)
  self.state == gen.state
end

#bytes(size) ⇒ Object 



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# File 'lib/crypt/isaac.rb', line 97

def bytes(size)
  buffer = ""
  ( size / 4 ).times { buffer << [rand(4294967295)].pack("L").unpack("aaaa").join }

  if size % 4 != 0
    buffer << [rand(4294967295)].pack("L").unpack("aaaa")[0..(size % 4 - 1)].join
  end

  buffer
end

#isaac ⇒ Object 



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# File 'lib/crypt/isaac.rb', line 108

def isaac
  i = 0
  x = 0
  y = 0

  @cc += 1
  @bb += @cc
  @bb & 0xffffffff

  while (i < 256) do 
    x = @mm[i]
    @aa = (@mm[(i + 128) & 255] + (@aa^(@aa << 13)) ) & 0xffffffff
    @mm[i] = y = (@mm[(x>>2)&255] + @aa + @bb ) & 0xffffffff
    @randrsl[i] = @bb = (@mm[(y>>10)&255] + x ) & 0xffffffff
    i += 1

    x = @mm[i]
    @aa = (@mm[(i+128)&255] + (@aa^(0x03ffffff & (@aa >> 6))) ) & 0xffffffff
    @mm[i] = y = (@mm[(x>>2)&255] + @aa + @bb ) & 0xffffffff
    @randrsl[i] = @bb = (@mm[(y>>10)&255] + x ) & 0xffffffff
    i += 1

    x = @mm[i]
    @aa = (@mm[(i + 128)&255] + (@aa^(@aa << 2)) ) & 0xffffffff
    @mm[i] = y = (@mm[(x>>2)&255] + @aa + @bb ) & 0xffffffff
    @randrsl[i] = @bb = (@mm[(y>>10)&255] + x ) & 0xffffffff
    i += 1

    x = @mm[i]
    @aa = (@mm[(i+128)&255] + (@aa^(0x0000ffff & (@aa >> 16))) ) & 0xffffffff
    @mm[i] = y = (@mm[(x>>2)&255] + @aa + @bb ) & 0xffffffff
    @randrsl[i] = @bb = (@mm[(y>>10)&255] + x ) & 0xffffffff
    i += 1
  end
end

#rand(arg = nil) ⇒ Object

Works just like the standard rand() function. If called with an integer argument, rand() will return positive random number in the range of 0 to (argument - 1). If called without an integer argument, rand() returns a positive floating point number less than 1. If called with a Range, returns a number that is in the range.



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# File 'lib/crypt/isaac.rb', line 68

def rand(arg = nil)
  if (@randcnt == 1)
    isaac
    @randcnt = 256
  end
  @randcnt -= 1
  if arg.nil?
    ( @randrsl[@randcnt] / 536870912.0 ) % 1
  elsif Integer === arg || Float === arg
    @randrsl[@randcnt] % arg
  elsif Range === arg
    arg.min + @randrsl[@randcnt] % (arg.max - arg.min)
  else
    @randrsl[@randcnt] % Integer(arg)
  end
end

#randinit(flag) ⇒ Object 



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# File 'lib/crypt/isaac.rb', line 144

def randinit(flag)
  i = 0
  a = 0
  b = 0
  c = 0
  d = 0
  e = 0
  f = 0
  g = 0
  @aa = @bb = @cc = 0
  a = b = c = d = e = f = g = h = 0x9e3779b9

  while (i < 4) do
    a ^= b<<1; d += a; b += c
    b ^= 0x3fffffff & (c>>2); e += b; c += d
    c ^= d << 8; f += c; d += e
    d ^= 0x0000ffff & (e >> 16); g += d; e += f
    e ^= f << 10; h += e; f += g
    f ^= 0x0fffffff & (g >> 4); a += f; g += h
    g ^= h << 8; b += g; h += a
    h ^= 0x007fffff & (a >> 9); c += h; a += b
    i += 1
  end

  i = 0
  while (i < 256) do
    if (flag)
      a+=@randrsl[i  ].to_i; b+=@randrsl[i+1].to_i;
      c+=@randrsl[i+2]; d+=@randrsl[i+3];
      e+=@randrsl[i+4]; f+=@randrsl[i+5];
      g+=@randrsl[i+6]; h+=@randrsl[i+7];
    end

    a^=b<<11; d+=a; b+=c;
    b^=0x3fffffff & (c>>2);  e+=b; c+=d;
    c^=d<<8;  f+=c; d+=e;
    d^=0x0000ffff & (e>>16); g+=d; e+=f;
    e^=f<<10; h+=e; f+=g;
    f^=0x0fffffff & (g>>4);  a+=f; g+=h;
    g^=h<<8;  b+=g; h+=a;
    h^=0x007fffff & (a>>9);  c+=h; a+=b;
    @mm[i]=a;@mm[i+1]=b; @mm[i+2]=c; @mm[i+3]=d;
    @mm[i+4]=e; @mm[i+5]=f; @mm[i+6]=g; @mm[i+7]=h;
    i += 8
  end

  if flag
    i = 0
    while (i < 256)
      a+=@mm[i  ]; b+=@mm[i+1]; c+=@mm[i+2]; d+=@mm[i+3];
      e+=@mm[i+4]; f+=@mm[i+5]; g+=@mm[i+6]; h+=@mm[i+7];
      a^=b<<11; d+=a; b+=c;
      b^=0x3fffffff & (c>>2);  e+=b; c+=d;
      c^=d<<8;  f+=c; d+=e;
      d^=0x0000ffff & (e>>16); g+=d; e+=f;
      e^=f<<10; h+=e; f+=g;
      f^=0x0fffffff & (g>>4);  a+=f; g+=h;
      g^=h<<8;  b+=g; h+=a;
      h^=0x007fffff & (a>>9);  c+=h; a+=b;
      @mm[i  ]=a; @mm[i+1]=b; @mm[i+2]=c; @mm[i+3]=d;
      @mm[i+4]=e; @mm[i+5]=f; @mm[i+6]=g; @mm[i+7]=h;
      i += 8
    end
  end

  isaac()
  @randcnt=256;        # /* prepare to use the first set of results */
end

#seed ⇒ Object 



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# File 'lib/crypt/isaac.rb', line 85

def seed
  Random === @seed ? @seed.seed : @seed
end

#srand(seed) ⇒ Object

If seeded with an integer, use that to seed a standard Ruby Mersenne Twister PRNG, and then use that to generate seed value for ISAAC. This is mostly useful for producing repeated, deterministic results, which may be needed for testing.



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# File 'lib/crypt/isaac.rb', line 52

def srand(seed)
  @seed = seed
  @randrsl = []
  seed_prng = ( Random === seed ) ? seed : Random.new(seed)
  256.times do |t|
    @randrsl[t] = seed_prng.rand(4294967295)
  end
  randinit(true)
end

#state ⇒ Object 



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# File 'lib/crypt/isaac.rb', line 89

def state
  @randrsl + [@randcnt]
end