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package org.bouncycastle.pqc.crypto.ntru;
import java.nio.ByteBuffer;
import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.Digest;
import org.bouncycastle.pqc.math.ntru.polynomial.IntegerPolynomial;
import org.bouncycastle.pqc.math.ntru.polynomial.Polynomial;
/**
* Signs, verifies data and generates key pairs.
* @deprecated the NTRUSigner algorithm was broken in 2012 by Ducas and Nguyen. See
*
* https://www.di.ens.fr/~ducas/NTRUSign_Cryptanalysis/DucasNguyen_Learning.pdf
* for details.
*/
public class NTRUSigner
{
private NTRUSigningParameters params;
private Digest hashAlg;
private NTRUSigningPrivateKeyParameters signingKeyPair;
private NTRUSigningPublicKeyParameters verificationKey;
/**
* Constructs a new instance with a set of signature parameters.
*
* @param params signature parameters
*/
public NTRUSigner(NTRUSigningParameters params)
{
this.params = params;
}
/**
* Resets the engine for signing a message.
*
* @param forSigning
* @param params
*/
public void init(boolean forSigning, CipherParameters params)
{
if (forSigning)
{
this.signingKeyPair = (NTRUSigningPrivateKeyParameters)params;
}
else
{
this.verificationKey = (NTRUSigningPublicKeyParameters)params;
}
hashAlg = this.params.hashAlg;
hashAlg.reset();
}
/**
* Adds data to sign or verify.
*
* @param b data
*/
public void update(byte b)
{
if (hashAlg == null)
{
throw new IllegalStateException("Call initSign or initVerify first!");
}
hashAlg.update(b);
}
/**
* Adds data to sign or verify.
*
* @param m data
* @param off offset
* @param length number of bytes
*/
public void update(byte[] m, int off, int length)
{
if (hashAlg == null)
{
throw new IllegalStateException("Call initSign or initVerify first!");
}
hashAlg.update(m, off, length);
}
/**
* Adds data to sign and computes a signature over this data and any data previously added via {@link #update(byte[], int, int)}.
*
* @return a signature
* @throws IllegalStateException if initSign was not called
*/
public byte[] generateSignature()
{
if (hashAlg == null || signingKeyPair == null)
{
throw new IllegalStateException("Call initSign first!");
}
byte[] msgHash = new byte[hashAlg.getDigestSize()];
hashAlg.doFinal(msgHash, 0);
return signHash(msgHash, signingKeyPair);
}
private byte[] signHash(byte[] msgHash, NTRUSigningPrivateKeyParameters kp)
{
int r = 0;
IntegerPolynomial s;
IntegerPolynomial i;
NTRUSigningPublicKeyParameters kPub = kp.getPublicKey();
do
{
r++;
if (r > params.signFailTolerance)
{
throw new IllegalStateException("Signing failed: too many retries (max=" + params.signFailTolerance + ")");
}
i = createMsgRep(msgHash, r);
s = sign(i, kp);
}
while (!verify(i, s, kPub.h));
byte[] rawSig = s.toBinary(params.q);
ByteBuffer sbuf = ByteBuffer.allocate(rawSig.length + 4);
sbuf.put(rawSig);
sbuf.putInt(r);
return sbuf.array();
}
private IntegerPolynomial sign(IntegerPolynomial i, NTRUSigningPrivateKeyParameters kp)
{
int N = params.N;
int q = params.q;
int perturbationBases = params.B;
NTRUSigningPrivateKeyParameters kPriv = kp;
NTRUSigningPublicKeyParameters kPub = kp.getPublicKey();
IntegerPolynomial s = new IntegerPolynomial(N);
int iLoop = perturbationBases;
while (iLoop >= 1)
{
Polynomial f = kPriv.getBasis(iLoop).f;
Polynomial fPrime = kPriv.getBasis(iLoop).fPrime;
IntegerPolynomial y = f.mult(i);
y.div(q);
y = fPrime.mult(y);
IntegerPolynomial x = fPrime.mult(i);
x.div(q);
x = f.mult(x);
IntegerPolynomial si = y;
si.sub(x);
s.add(si);
IntegerPolynomial hi = (IntegerPolynomial)kPriv.getBasis(iLoop).h.clone();
if (iLoop > 1)
{
hi.sub(kPriv.getBasis(iLoop - 1).h);
}
else
{
hi.sub(kPub.h);
}
i = si.mult(hi, q);
iLoop--;
}
Polynomial f = kPriv.getBasis(0).f;
Polynomial fPrime = kPriv.getBasis(0).fPrime;
IntegerPolynomial y = f.mult(i);
y.div(q);
y = fPrime.mult(y);
IntegerPolynomial x = fPrime.mult(i);
x.div(q);
x = f.mult(x);
y.sub(x);
s.add(y);
s.modPositive(q);
return s;
}
/**
* Verifies a signature for any data previously added via {@link #update(byte[], int, int)}.
*
* @param sig a signature
* @return whether the signature is valid
* @throws IllegalStateException if initVerify was not called
*/
public boolean verifySignature(byte[] sig)
{
if (hashAlg == null || verificationKey == null)
{
throw new IllegalStateException("Call initVerify first!");
}
byte[] msgHash = new byte[hashAlg.getDigestSize()];
hashAlg.doFinal(msgHash, 0);
return verifyHash(msgHash, sig, verificationKey);
}
private boolean verifyHash(byte[] msgHash, byte[] sig, NTRUSigningPublicKeyParameters pub)
{
ByteBuffer sbuf = ByteBuffer.wrap(sig);
byte[] rawSig = new byte[sig.length - 4];
sbuf.get(rawSig);
IntegerPolynomial s = IntegerPolynomial.fromBinary(rawSig, params.N, params.q);
int r = sbuf.getInt();
return verify(createMsgRep(msgHash, r), s, pub.h);
}
private boolean verify(IntegerPolynomial i, IntegerPolynomial s, IntegerPolynomial h)
{
int q = params.q;
double normBoundSq = params.normBoundSq;
double betaSq = params.betaSq;
IntegerPolynomial t = h.mult(s, q);
t.sub(i);
long centeredNormSq = (long)(s.centeredNormSq(q) + betaSq * t.centeredNormSq(q));
return centeredNormSq <= normBoundSq;
}
protected IntegerPolynomial createMsgRep(byte[] msgHash, int r)
{
int N = params.N;
int q = params.q;
int c = 31 - Integer.numberOfLeadingZeros(q);
int B = (c + 7) / 8;
IntegerPolynomial i = new IntegerPolynomial(N);
ByteBuffer cbuf = ByteBuffer.allocate(msgHash.length + 4);
cbuf.put(msgHash);
cbuf.putInt(r);
NTRUSignerPrng prng = new NTRUSignerPrng(cbuf.array(), params.hashAlg);
for (int t = 0; t < N; t++)
{
byte[] o = prng.nextBytes(B);
int hi = o[o.length - 1];
hi >>= 8 * B - c;
hi <<= 8 * B - c;
o[o.length - 1] = (byte)hi;
ByteBuffer obuf = ByteBuffer.allocate(4);
obuf.put(o);
obuf.rewind();
// reverse byte order so it matches the endianness of java ints
i.coeffs[t] = Integer.reverseBytes(obuf.getInt());
}
return i;
}
}
