/*
Licensed to the Apache Software Foundation (ASF) under one
or more contributor license agreements.  See the NOTICE file
distributed with this work for additional information
regarding copyright ownership.  The ASF licenses this file
to you under the Apache License, Version 2.0 (the
"License"); you may not use this file except in compliance
with the License.  You may obtain a copy of the License at

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

Unless required by applicable law or agreed to in writing,
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 static final int NK=21;
	private static final int NJ=6;
	private static final int NV=8;
	private int[] ira=new int[NK];  /* random number...   */
	private int rndptr;   /* ...array & pointer */
	private int borrow;
	private int pool_ptr;
	private byte[] pool=new byte[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]=(int)(pdiff&0xffffffffL);
		}

		return ira[0];
	}

	public 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(byte[] 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 void seed(int rawlen,byte[] raw)
	{ /* initialise from at least 128 byte string of raw random entropy */
		int i;
		byte [] digest;
		byte [] b=new byte[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 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 int getByte()
	{
		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());
	} */
}