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package org.spongycastle.pqc.crypto.gmss.util;
import org.spongycastle.crypto.Digest;
/**
* This class provides a PRNG for GMSS
*/
public class GMSSRandom
{
/**
* Hash function for the construction of the authentication trees
*/
private Digest messDigestTree;
/**
* Constructor
*
* @param messDigestTree2
*/
public GMSSRandom(Digest messDigestTree2)
{
this.messDigestTree = messDigestTree2;
}
/**
* computes the next seed value, returns a random byte array and sets
* outseed to the next value
*
* @param outseed byte array in which ((1 + SEEDin +RAND) mod 2^n) will be
* stored
* @return byte array of H(SEEDin)
*/
public byte[] nextSeed(byte[] outseed)
{
// RAND <-- H(SEEDin)
byte[] rand = new byte[outseed.length];
messDigestTree.update(outseed, 0, outseed.length);
rand = new byte[messDigestTree.getDigestSize()];
messDigestTree.doFinal(rand, 0);
// SEEDout <-- (1 + SEEDin +RAND) mod 2^n
addByteArrays(outseed, rand);
addOne(outseed);
// System.arraycopy(outseed, 0, outseed, 0, outseed.length);
return rand;
}
private void addByteArrays(byte[] a, byte[] b)
{
byte overflow = 0;
int temp;
for (int i = 0; i < a.length; i++)
{
temp = (0xFF & a[i]) + (0xFF & b[i]) + overflow;
a[i] = (byte)temp;
overflow = (byte)(temp >> 8);
}
}
private void addOne(byte[] a)
{
byte overflow = 1;
int temp;
for (int i = 0; i < a.length; i++)
{
temp = (0xFF & a[i]) + overflow;
a[i] = (byte)temp;
overflow = (byte)(temp >> 8);
}
}
}
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