/// <summary>
/// The McEliece decryption primitive
/// </summary>
///
/// <param name="PrivateKey">The private key</param>
/// <param name="C">The ciphertext vector <c>c = m*G + z</c></param>
///
/// <returns>The message vector <c>m</c> and the error vector <c>z</c></returns>
public static GF2Vector[] Decrypt(MPKCPrivateKey PrivateKey, GF2Vector C)
{
// obtain values from private key
int k = PrivateKey.K;
Permutation p = PrivateKey.P1;
GF2mField field = PrivateKey.GF;
PolynomialGF2mSmallM gp = PrivateKey.GP;
GF2Matrix h = PrivateKey.H;
PolynomialGF2mSmallM[] q = PrivateKey.QInv;
// 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 });
}
/// <summary>
/// The McEliece decryption primitive
/// </summary>
///
/// <param name="PrivateKey">The private key</param>
/// <param name="C">The ciphertext vector <c>c = m*G + z</c></param>
///
/// <returns>The message vector <c>m</c> and the error vector <c>z</c></returns>
public static GF2Vector[] Decrypt(MPKCPrivateKey PrivateKey, GF2Vector C)
{
// obtain values from private key
int k = PrivateKey.K;
Permutation p = PrivateKey.P1;
GF2mField field = PrivateKey.GF;
PolynomialGF2mSmallM gp = PrivateKey.GP;
GF2Matrix h = PrivateKey.H;
PolynomialGF2mSmallM[] q = PrivateKey.QInv;
// 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 };
}
private void TestEncode()
{
MPKCParameters mpar = (MPKCParameters)MPKCParamSets.MPKCFM11T40S256.DeepCopy();
MPKCKeyGenerator mkgen = new MPKCKeyGenerator(mpar);
IAsymmetricKeyPair akp = mkgen.GenerateKeyPair();
MPKCPublicKey pub = (MPKCPublicKey)akp.PublicKey;
byte[] enc = pub.ToBytes();
using (MPKCPublicKey pub2 = MPKCPublicKey.From(enc))
{
if (!pub.Equals(pub2))
{
throw new Exception("EncryptionKey: public key comparison test failed!");
}
if (pub.GetHashCode() != pub2.GetHashCode())
{
throw new Exception("EncryptionKey: public key hash test failed!");
}
}
OnProgress(new TestEventArgs("Passed public key serialization"));
MemoryStream pubstr = pub.ToStream();
using (MPKCPublicKey pub2 = MPKCPublicKey.From(pubstr))
{
if (!pub.Equals(pub2))
{
throw new Exception("EncryptionKey: public key comparison test failed!");
}
if (pub.GetHashCode() != pub2.GetHashCode())
{
throw new Exception("EncryptionKey: public key hash test failed!");
}
}
pubstr.Dispose();
OnProgress(new TestEventArgs("Passed public key stream test"));
MPKCPrivateKey pri = (MPKCPrivateKey)akp.PrivateKey;
enc = pri.ToBytes();
using (MPKCPrivateKey pri2 = new MPKCPrivateKey(enc))
{
if (!pri.Equals(pri2))
{
throw new Exception("EncryptionKey: private key comparison test failed!");
}
if (pri.GetHashCode() != pri2.GetHashCode())
{
throw new Exception("EncryptionKey: private key hash test failed!");
}
}
OnProgress(new TestEventArgs("Passed private key serialization"));
MemoryStream pristr = pri.ToStream();
using (MPKCPrivateKey pri2 = MPKCPrivateKey.From(pristr))
{
if (!pri.Equals(pri2))
{
throw new Exception("EncryptionKey: private key comparison test failed!");
}
if (pri.GetHashCode() != pri2.GetHashCode())
{
throw new Exception("EncryptionKey: private key hash test failed!");
}
}
pristr.Dispose();
OnProgress(new TestEventArgs("Passed private key stream test"));
using (MPKCEncrypt mpe = new MPKCEncrypt(mpar))
{
mpe.Initialize(akp.PublicKey);
int sz = mpe.MaxPlainText - 1;
byte[] data = new byte[sz];
new VTDev.Libraries.CEXEngine.Crypto.Prng.CSPPrng().GetBytes(data);
enc = mpe.Encrypt(data);
mpe.Initialize(akp.PrivateKey);
byte[] dec = mpe.Decrypt(enc);
if (!Evaluate.AreEqual(dec, data))
{
throw new Exception("EncryptionKey: decryption failure!");
}
OnProgress(new TestEventArgs("Passed encryption test"));
}
pri.Dispose();
pub.Dispose();
}
