cs/RAND.cs

/*
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regarding copyright ownership.  The ASF licenses this file
to you under the Apache License, Version 2.0 (the
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with the License.  You may obtain a copy of the License at

  http://www.apache.org/licenses/LICENSE-2.0

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software distributed under the License is distributed on an
"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
KIND, either express or implied.  See the License for the
specific language governing permissions and limitations
under the License.
*/

/*
 *   Cryptographic strong random number generator
 *
 *   Unguessable seed -> SHA -> PRNG internal state -> SHA -> random numbers
 *   Slow - but secure
 *
 *   See ftp://ftp.rsasecurity.com/pub/pdfs/bull-1.pdf for a justification
 */

/* Marsaglia & Zaman Random number generator constants */


public class RAND
{
/* Cryptographically strong pseudo-random number generator */

	private const int NK = 21;
	private const int NJ = 6;
	private const int NV = 8;
	private int[] ira = new int[NK]; // random number...
	private int rndptr; // ...array & pointer
	private int borrow;
	private int pool_ptr;
	private sbyte[] pool = new sbyte[32]; // random pool

	public RAND()
	{
		clean();
	}

	private int sbrand()
	{ // Marsaglia & Zaman random number generator
		int i, k;
		long pdiff, t;

		rndptr++;
		if (rndptr < NK)
		{
			return ira[rndptr];
		}
		rndptr = 0;
		for (i = 0,k = NK - NJ;i < NK;i++,k++)
		{ // calculate next NK values
			if (k == NK)
			{
				k = 0;
			}
			t = ((long)ira[k]) & 0xffffffffL;
			pdiff = (t - (((long)ira[i]) & 0xffffffffL) - (long)borrow) & 0xffffffffL;
			if (pdiff < t)
			{
				borrow = 0;
			}
			if (pdiff > t)
			{
				borrow = 1;
			}
			ira[i] = unchecked((int)(pdiff & 0xffffffffL));
		}

		return ira[0];
	}

	public virtual void sirand(int seed)
	{
		int i, @in;
		int t , m = 1;
		borrow = 0;
		rndptr = 0;
		ira[0] ^= seed;
		for (i = 1;i < NK;i++)
		{ // fill initialisation vector
			@in = (NV * i) % NK;
			ira[@in] ^= m; // note XOR
			t = m;
			m = seed - m;
			seed = t;
		}
		for (i = 0;i < 10000;i++)
		{
			sbrand(); // "warm-up" & stir the generator
		}
	}

	private void fill_pool()
	{
		HASH sh = new HASH();
		for (int i = 0;i < 128;i++)
		{
			sh.process(sbrand());
		}
		pool = sh.hash();
		pool_ptr = 0;
	}

	private static int pack(sbyte[] b)
	{ // pack 4 bytes into a 32-bit Word
		return ((((int)b[3]) & 0xff) << 24) | (((int)b[2] & 0xff) << 16) | (((int)b[1] & 0xff) << 8) | ((int)b[0] & 0xff);
	}

/* Initialize RNG with some real entropy from some external source */
	public virtual void seed(int rawlen, sbyte[] raw)
	{ // initialise from at least 128 byte string of raw random entropy
		int i;
		sbyte[] digest;
		sbyte[] b = new sbyte[4];
		HASH sh = new HASH();
		pool_ptr = 0;
		for (i = 0;i < NK;i++)
		{
			ira[i] = 0;
		}
		if (rawlen > 0)
		{
			for (i = 0;i < rawlen;i++)
			{
				sh.process(raw[i]);
			}
			digest = sh.hash();

/* initialise PRNG from distilled randomness */

			for (i = 0;i < 8;i++)
			{
				b[0] = digest[4 * i];
				b[1] = digest[4 * i + 1];
				b[2] = digest[4 * i + 2];
				b[3] = digest[4 * i + 3];
				sirand(pack(b));
			}
		}
		fill_pool();
	}

/* Terminate and clean up */
	public virtual void clean()
	{ // kill internal state
		int i;
		pool_ptr = rndptr = 0;
		for (i = 0;i < 32;i++)
		{
			pool[i] = 0;
		}
		for (i = 0;i < NK;i++)
		{
			ira[i] = 0;
		}
		borrow = 0;
	}

/* get random byte */
	public virtual int Byte
	{
		get
		{
			int r;
			r = pool[pool_ptr++];
			if (pool_ptr >= 32)
			{
				fill_pool();
			}
			return (r & 0xff);
		}
	}

/* test main program */
/*
	public static void main(String[] args) {
		int i;
		byte[] raw=new byte[100];
		RAND rng=new RAND();

		rng.clean();
		for (i=0;i<100;i++) raw[i]=(byte)i;

		rng.seed(100,raw);

		for (i=0;i<1000;i++)
			System.out.format("%03d ",rng.getByte());
	} */
}