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(noblock = 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(noblock = true)
	@mm = []
	@randrsl = []
	# Best initialization of the generator would be by pulling
	# numbers from /dev/random.
	rnd_source = noblock ? '/dev/urandom' : '/dev/random'
	if (FileTest.exist? rnd_source)
		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
	else
		# If urandom isn't available, the standard Ruby PRNG makes an
		# adequate fallback.
		256.times do |t|
			@randrsl[t] = Kernel.rand(4294967295)
		end
	end
	randinit(true)
	nil
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

#isaac ⇒ Object 



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# File 'lib/crypt-isaac.rb', line 66

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(*num) ⇒ 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.



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# File 'lib/crypt-isaac.rb', line 53

def rand(*num)
	if (@randcnt == 1)
		isaac
		@randcnt = 256
	end
	@randcnt -= 1
	if num[0].to_i > 0
		@randrsl[@randcnt].modulo(num[0])
	else
		".#{@randrsl[@randcnt]}".to_f
	end
end

#randinit(flag) ⇒ Object 



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# File 'lib/crypt-isaac.rb', line 102

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