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package org.bouncycastle.pqc.crypto.gmss.util;
import org.bouncycastle.crypto.Digest;
/**
* This class implements signature verification of the Winternitz one-time
* signature scheme (OTSS), described in C.Dods, N.P. Smart, and M. Stam, "Hash
* Based Digital Signature Schemes", LNCS 3796, pages 96–115, 2005. The
* class is used by the GMSS classes.
*/
public class WinternitzOTSVerify
{
private Digest messDigestOTS;
private int mdsize;
/**
* The Winternitz parameter
*/
private int w;
/**
* The constructor
*
* @param digest the name of the hash function used by the OTS and the provider
* name of the hash function
* @param w the Winternitz parameter
*/
public WinternitzOTSVerify(Digest digest, int w)
{
this.w = w;
messDigestOTS = digest;
mdsize = messDigestOTS.getDigestSize();
}
/**
* @return The length of the one-time signature
*/
public int getSignatureLength()
{
int mdsize = messDigestOTS.getDigestSize();
int size = ((mdsize << 3) + (w - 1)) / w;
int logs = getLog((size << w) + 1);
size += (logs + w - 1) / w;
return mdsize * size;
}
/**
* This method computes the public OTS key from the one-time signature of a
* message. This is *NOT* a complete OTS signature verification, but it
* suffices for usage with CMSS.
*
* @param message the message
* @param signature the one-time signature
* @return The public OTS key
*/
public byte[] Verify(byte[] message, byte[] signature)
{
byte[] hash = new byte[mdsize]; // hash of message m
// create hash of message m
messDigestOTS.update(message, 0, message.length);
messDigestOTS.doFinal(hash, 0);
int size = ((mdsize << 3) + (w - 1)) / w;
int logs = getLog((size << w) + 1);
int keysize = size + (logs + w - 1) / w;
int testKeySize = mdsize * keysize;
if (testKeySize != signature.length)
{
return null;
}
byte[] testKey = new byte[testKeySize];
int c = 0;
int counter = 0;
int test;
if (8 % w == 0)
{
int d = 8 / w;
int k = (1 << w) - 1;
// verify signature
for (int i = 0; i < hash.length; i++)
{
for (int j = 0; j < d; j++)
{
test = hash[i] & k;
c += test;
hashSignatureBlock(signature, counter * mdsize, k - test, testKey, counter * mdsize);
hash[i] = (byte)(hash[i] >>> w);
counter++;
}
}
c = (size << w) - c;
for (int i = 0; i < logs; i += w)
{
test = c & k;
hashSignatureBlock(signature, counter * mdsize, k - test, testKey, counter * mdsize);
c >>>= w;
counter++;
}
}
else if (w < 8)
{
int d = mdsize / w;
int k = (1 << w) - 1;
long big8;
int ii = 0;
// create signature
// first d*w bytes of hash
for (int i = 0; i < d; i++)
{
big8 = 0;
for (int j = 0; j < w; j++)
{
big8 ^= (hash[ii] & 0xff) << (j << 3);
ii++;
}
for (int j = 0; j < 8; j++)
{
test = (int)(big8 & k);
c += test;
hashSignatureBlock(signature, counter * mdsize, k - test, testKey, counter * mdsize);
big8 >>>= w;
counter++;
}
}
// rest of hash
d = mdsize % w;
big8 = 0;
for (int j = 0; j < d; j++)
{
big8 ^= (hash[ii] & 0xff) << (j << 3);
ii++;
}
d <<= 3;
for (int j = 0; j < d; j += w)
{
test = (int)(big8 & k);
c += test;
hashSignatureBlock(signature, counter * mdsize, k - test, testKey, counter * mdsize);
big8 >>>= w;
counter++;
}
// check bytes
c = (size << w) - c;
for (int i = 0; i < logs; i += w)
{
test = c & k;
hashSignatureBlock(signature, counter * mdsize, k - test, testKey, counter * mdsize);
c >>>= w;
counter++;
}
}// end if(w<8)
else if (w < 57)
{
int d = (mdsize << 3) - w;
int k = (1 << w) - 1;
byte[] hlp = new byte[mdsize];
long big8, test8;
int r = 0;
int s, f, rest, ii;
// create signature
// first a*w bits of hash where a*w <= 8*mdsize < (a+1)*w
while (r <= d)
{
s = r >>> 3;
rest = r % 8;
r += w;
f = (r + 7) >>> 3;
big8 = 0;
ii = 0;
for (int j = s; j < f; j++)
{
big8 ^= (hash[j] & 0xff) << (ii << 3);
ii++;
}
big8 >>>= rest;
test8 = (big8 & k);
c += test8;
System.arraycopy(signature, counter * mdsize, hlp, 0, mdsize);
while (test8 < k)
{
messDigestOTS.update(hlp, 0, hlp.length);
messDigestOTS.doFinal(hlp, 0);
test8++;
}
System.arraycopy(hlp, 0, testKey, counter * mdsize, mdsize);
counter++;
}
// rest of hash
s = r >>> 3;
if (s < mdsize)
{
rest = r % 8;
big8 = 0;
ii = 0;
for (int j = s; j < mdsize; j++)
{
big8 ^= (hash[j] & 0xff) << (ii << 3);
ii++;
}
big8 >>>= rest;
test8 = (big8 & k);
c += test8;
System.arraycopy(signature, counter * mdsize, hlp, 0, mdsize);
while (test8 < k)
{
messDigestOTS.update(hlp, 0, hlp.length);
messDigestOTS.doFinal(hlp, 0);
test8++;
}
System.arraycopy(hlp, 0, testKey, counter * mdsize, mdsize);
counter++;
}
// check bytes
c = (size << w) - c;
for (int i = 0; i < logs; i += w)
{
test8 = (c & k);
System.arraycopy(signature, counter * mdsize, hlp, 0, mdsize);
while (test8 < k)
{
messDigestOTS.update(hlp, 0, hlp.length);
messDigestOTS.doFinal(hlp, 0);
test8++;
}
System.arraycopy(hlp, 0, testKey, counter * mdsize, mdsize);
c >>>= w;
counter++;
}
}// end if(w<57)
messDigestOTS.update(testKey, 0, testKey.length);
byte[] TKey = new byte[mdsize];
messDigestOTS.doFinal(TKey, 0);
return TKey;
}
/**
* This method returns the least integer that is greater or equal to the
* logarithm to the base 2 of an integer intValue.
*
* @param intValue an integer
* @return The least integer greater or equal to the logarithm to the base
* 256 of intValue
*/
public int getLog(int intValue)
{
int log = 1;
int i = 2;
while (i < intValue)
{
i <<= 1;
log++;
}
return log;
}
private void hashSignatureBlock(byte[] sig, int sigOff, int rounds, byte[] buf, int bufOff)
{
if (rounds < 1)
{
System.arraycopy(sig, sigOff, buf, bufOff, mdsize);
}
else
{
messDigestOTS.update(sig, sigOff, mdsize);
messDigestOTS.doFinal(buf, bufOff);
while (--rounds > 0)
{
messDigestOTS.update(buf, bufOff, mdsize);
messDigestOTS.doFinal(buf, bufOff);
}
}
}
}