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package org.bouncycastle.pqc.crypto.mceliece;
import org.bouncycastle.pqc.math.linearalgebra.GF2Matrix;
import org.bouncycastle.pqc.math.linearalgebra.GF2Vector;
import org.bouncycastle.pqc.math.linearalgebra.GF2mField;
import org.bouncycastle.pqc.math.linearalgebra.GoppaCode;
import org.bouncycastle.pqc.math.linearalgebra.Permutation;
import org.bouncycastle.pqc.math.linearalgebra.PolynomialGF2mSmallM;
import org.bouncycastle.pqc.math.linearalgebra.Vector;
/**
* Core operations for the CCA-secure variants of McEliece.
*/
public final class McElieceCCA2Primitives
{
/**
* Default constructor (private).
*/
private McElieceCCA2Primitives()
{
}
/**
* The McEliece encryption primitive.
*
* @param pubKey the public key
* @param m the message vector
* @param z the error vector
* @return <tt>m*G + z</tt>
*/
public static GF2Vector encryptionPrimitive(McElieceCCA2PublicKeyParameters pubKey,
GF2Vector m, GF2Vector z)
{
GF2Matrix matrixG = pubKey.getMatrixG();
Vector mG = matrixG.leftMultiplyLeftCompactForm(m);
return (GF2Vector)mG.add(z);
}
/**
* The McEliece decryption primitive.
*
* @param privKey the private key
* @param c the ciphertext vector <tt>c = m*G + z</tt>
* @return the message vector <tt>m</tt> and the error vector <tt>z</tt>
*/
public static GF2Vector[] decryptionPrimitive(
McElieceCCA2PrivateKeyParameters privKey, GF2Vector c)
{
// obtain values from private key
int k = privKey.getK();
Permutation p = privKey.getP();
GF2mField field = privKey.getField();
PolynomialGF2mSmallM gp = privKey.getGoppaPoly();
GF2Matrix h = privKey.getH();
PolynomialGF2mSmallM[] q = privKey.getQInv();
// compute inverse permutation P^-1
Permutation pInv = p.computeInverse();
// multiply c with permutation P^-1
GF2Vector cPInv = (GF2Vector)c.multiply(pInv);
// compute syndrome of cP^-1
GF2Vector syndVec = (GF2Vector)h.rightMultiply(cPInv);
// decode syndrome
GF2Vector errors = GoppaCode.syndromeDecode(syndVec, field, gp, q);
GF2Vector mG = (GF2Vector)cPInv.add(errors);
// multiply codeword and error vector with P
mG = (GF2Vector)mG.multiply(p);
errors = (GF2Vector)errors.multiply(p);
// extract plaintext vector (last k columns of mG)
GF2Vector m = mG.extractRightVector(k);
// return vectors
return new GF2Vector[]{m, errors};
}
}
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