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The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.4.
package org.bouncycastle.pqc.legacy.crypto.mceliece;
import java.security.SecureRandom;
import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.CryptoServicesRegistrar;
import org.bouncycastle.crypto.Digest;
import org.bouncycastle.crypto.InvalidCipherTextException;
import org.bouncycastle.crypto.digests.SHA1Digest;
import org.bouncycastle.crypto.params.ParametersWithRandom;
import org.bouncycastle.crypto.prng.DigestRandomGenerator;
import org.bouncycastle.pqc.crypto.MessageEncryptor;
import org.bouncycastle.pqc.legacy.math.linearalgebra.ByteUtils;
import org.bouncycastle.pqc.legacy.math.linearalgebra.GF2Vector;
/**
* This class implements the Pointcheval conversion of the McEliecePKCS.
* Pointcheval presents a generic technique to make a CCA2-secure cryptosystem
* from any partially trapdoor one-way function in the random oracle model. For
* details, see D. Engelbert, R. Overbeck, A. Schmidt, "A Summary of McEliece-Type Cryptosystems and their Security", technical report.
* https://www.degruyter.com/document/doi/10.1515/JMC.2007.009/html
*/
public class McEliecePointchevalCipher
implements MessageEncryptor
{
/**
* The OID of the algorithm.
*/
public static final String OID = "1.3.6.1.4.1.8301.3.1.3.4.2.2";
private Digest messDigest;
private SecureRandom sr;
/**
* The McEliece main parameters
*/
private int n, k, t;
McElieceCCA2KeyParameters key;
private boolean forEncryption;
public void init(boolean forEncryption,
CipherParameters param)
{
this.forEncryption = forEncryption;
if (forEncryption)
{
if (param instanceof ParametersWithRandom)
{
ParametersWithRandom rParam = (ParametersWithRandom)param;
this.sr = rParam.getRandom();
this.key = (McElieceCCA2PublicKeyParameters)rParam.getParameters();
this.initCipherEncrypt((McElieceCCA2PublicKeyParameters)key);
}
else
{
this.sr = CryptoServicesRegistrar.getSecureRandom();
this.key = (McElieceCCA2PublicKeyParameters)param;
this.initCipherEncrypt((McElieceCCA2PublicKeyParameters)key);
}
}
else
{
this.key = (McElieceCCA2PrivateKeyParameters)param;
this.initCipherDecrypt((McElieceCCA2PrivateKeyParameters)key);
}
}
/**
* Return the key size of the given key object.
*
* @param key the McElieceCCA2KeyParameters object
* @return the key size of the given key object
* @throws IllegalArgumentException if the key is invalid
*/
public int getKeySize(McElieceCCA2KeyParameters key)
throws IllegalArgumentException
{
if (key instanceof McElieceCCA2PublicKeyParameters)
{
return ((McElieceCCA2PublicKeyParameters)key).getN();
}
if (key instanceof McElieceCCA2PrivateKeyParameters)
{
return ((McElieceCCA2PrivateKeyParameters)key).getN();
}
throw new IllegalArgumentException("unsupported type");
}
protected int decryptOutputSize(int inLen)
{
return 0;
}
protected int encryptOutputSize(int inLen)
{
return 0;
}
private void initCipherEncrypt(McElieceCCA2PublicKeyParameters pubKey)
{
this.messDigest = Utils.getDigest(pubKey.getDigest());
n = pubKey.getN();
k = pubKey.getK();
t = pubKey.getT();
}
private void initCipherDecrypt(McElieceCCA2PrivateKeyParameters privKey)
{
this.messDigest = Utils.getDigest(privKey.getDigest());
n = privKey.getN();
k = privKey.getK();
t = privKey.getT();
}
public byte[] messageEncrypt(byte[] input)
{
if (!forEncryption)
{
throw new IllegalStateException("cipher initialised for decryption");
}
int kDiv8 = k >> 3;
// generate random r of length k div 8 bytes
byte[] r = new byte[kDiv8];
sr.nextBytes(r);
// generate random vector r' of length k bits
GF2Vector rPrime = new GF2Vector(k, sr);
// convert r' to byte array
byte[] rPrimeBytes = rPrime.getEncoded();
// compute (input||r)
byte[] mr = ByteUtils.concatenate(input, r);
// compute H(input||r)
messDigest.update(mr, 0, mr.length);
byte[] hmr = new byte[messDigest.getDigestSize()];
messDigest.doFinal(hmr, 0);
// convert H(input||r) to error vector z
GF2Vector z = Conversions.encode(n, t, hmr);
// compute c1 = E(rPrime, z)
byte[] c1 = McElieceCCA2Primitives.encryptionPrimitive((McElieceCCA2PublicKeyParameters)key, rPrime,
z).getEncoded();
// get PRNG object
DigestRandomGenerator sr0 = new DigestRandomGenerator(new SHA1Digest());
// seed PRNG with r'
sr0.addSeedMaterial(rPrimeBytes);
// generate random c2
byte[] c2 = new byte[input.length + kDiv8];
sr0.nextBytes(c2);
// XOR with input
for (int i = 0; i < input.length; i++)
{
c2[i] ^= input[i];
}
// XOR with r
for (int i = 0; i < kDiv8; i++)
{
c2[input.length + i] ^= r[i];
}
// return (c1||c2)
return ByteUtils.concatenate(c1, c2);
}
public byte[] messageDecrypt(byte[] input)
throws InvalidCipherTextException
{
if (forEncryption)
{
throw new IllegalStateException("cipher initialised for decryption");
}
int c1Len = (n + 7) >> 3;
int c2Len = input.length - c1Len;
// split cipher text (c1||c2)
byte[][] c1c2 = ByteUtils.split(input, c1Len);
byte[] c1 = c1c2[0];
byte[] c2 = c1c2[1];
// decrypt c1 []
GF2Vector c1Vec = GF2Vector.OS2VP(n, c1);
GF2Vector[] c1Dec = McElieceCCA2Primitives.decryptionPrimitive((McElieceCCA2PrivateKeyParameters)key,
c1Vec);
byte[] rPrimeBytes = c1Dec[0].getEncoded();
// [] and obtain error vector z
GF2Vector z = c1Dec[1];
// get PRNG object
DigestRandomGenerator sr0 = new DigestRandomGenerator(new SHA1Digest());
// seed PRNG with r'
sr0.addSeedMaterial(rPrimeBytes);
// generate random sequence
byte[] mrBytes = new byte[c2Len];
sr0.nextBytes(mrBytes);
// XOR with c2 to obtain (m||r)
for (int i = 0; i < c2Len; i++)
{
mrBytes[i] ^= c2[i];
}
// compute H(m||r)
messDigest.update(mrBytes, 0, mrBytes.length);
byte[] hmr = new byte[messDigest.getDigestSize()];
messDigest.doFinal(hmr, 0);
// compute Conv(H(m||r))
c1Vec = Conversions.encode(n, t, hmr);
// check that Conv(H(m||r)) = z
if (!c1Vec.equals(z))
{
throw new InvalidCipherTextException("Bad Padding: Invalid ciphertext.");
}
// split (m||r) to obtain m
int kDiv8 = k >> 3;
byte[][] mr = ByteUtils.split(mrBytes, c2Len - kDiv8);
// return plain text m
return mr[0];
}
}