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package org.spongycastle.pqc.crypto.ntru;
import java.nio.ByteBuffer;
import org.spongycastle.crypto.Digest;
/**
* An implementation of the deterministic pseudo-random generator in EESS section 3.7.3.1
*/
public class NTRUSignerPrng
{
private int counter;
private byte[] seed;
private Digest hashAlg;
/**
* Constructs a new PRNG and seeds it with a byte array.
*
* @param seed a seed
* @param hashAlg the hash algorithm to use
*/
NTRUSignerPrng(byte[] seed, Digest hashAlg)
{
counter = 0;
this.seed = seed;
this.hashAlg = hashAlg;
}
/**
* Returns <code>n</code> random bytes
*
* @param n number of bytes to return
* @return the next <code>n</code> random bytes
*/
byte[] nextBytes(int n)
{
ByteBuffer buf = ByteBuffer.allocate(n);
while (buf.hasRemaining())
{
ByteBuffer cbuf = ByteBuffer.allocate(seed.length + 4);
cbuf.put(seed);
cbuf.putInt(counter);
byte[] array = cbuf.array();
byte[] hash = new byte[hashAlg.getDigestSize()];
hashAlg.update(array, 0, array.length);
hashAlg.doFinal(hash, 0);
if (buf.remaining() < hash.length)
{
buf.put(hash, 0, buf.remaining());
}
else
{
buf.put(hash);
}
counter++;
}
return buf.array();
}
}
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