public static AsymmetricKeyParameter CreateKey(
			SubjectPublicKeyInfo keyInfo)
        {
            AlgorithmIdentifier algID = keyInfo.AlgorithmID;
			DerObjectIdentifier algOid = algID.ObjectID;

			// TODO See RSAUtil.isRsaOid in Java build
			if (algOid.Equals(PkcsObjectIdentifiers.RsaEncryption)
				|| algOid.Equals(X509ObjectIdentifiers.IdEARsa)
				|| algOid.Equals(PkcsObjectIdentifiers.IdRsassaPss)
				|| algOid.Equals(PkcsObjectIdentifiers.IdRsaesOaep))
			{
				RsaPublicKeyStructure pubKey = RsaPublicKeyStructure.GetInstance(
					keyInfo.GetPublicKey());

				return new RsaKeyParameters(false, pubKey.Modulus, pubKey.PublicExponent);
			}
			else if (algOid.Equals(X9ObjectIdentifiers.DHPublicNumber))
			{
				Asn1Sequence seq = Asn1Sequence.GetInstance(algID.Parameters.ToAsn1Object());

				DHPublicKey dhPublicKey = DHPublicKey.GetInstance(keyInfo.GetPublicKey());

				BigInteger y = dhPublicKey.Y.Value;

				if (IsPkcsDHParam(seq))
					return ReadPkcsDHParam(algOid, y, seq);

				DHDomainParameters dhParams = DHDomainParameters.GetInstance(seq);

				BigInteger p = dhParams.P.Value;
				BigInteger g = dhParams.G.Value;
				BigInteger q = dhParams.Q.Value;

				BigInteger j = null;
				if (dhParams.J != null)
				{
					j = dhParams.J.Value;
				}

				DHValidationParameters validation = null;
				DHValidationParms dhValidationParms = dhParams.ValidationParms;
				if (dhValidationParms != null)
				{
					byte[] seed = dhValidationParms.Seed.GetBytes();
					BigInteger pgenCounter = dhValidationParms.PgenCounter.Value;

					// TODO Check pgenCounter size?

					validation = new DHValidationParameters(seed, pgenCounter.IntValue);
				}

				return new DHPublicKeyParameters(y, new DHParameters(p, g, q, j, validation));
			}
			else if (algOid.Equals(PkcsObjectIdentifiers.DhKeyAgreement))
			{
				Asn1Sequence seq = Asn1Sequence.GetInstance(algID.Parameters.ToAsn1Object());

				DerInteger derY = (DerInteger) keyInfo.GetPublicKey();

				return ReadPkcsDHParam(algOid, derY.Value, seq);
			}
			else if (algOid.Equals(OiwObjectIdentifiers.ElGamalAlgorithm))
			{
				ElGamalParameter para = new ElGamalParameter(
					Asn1Sequence.GetInstance(algID.Parameters.ToAsn1Object()));
				DerInteger derY = (DerInteger) keyInfo.GetPublicKey();

				return new ElGamalPublicKeyParameters(
					derY.Value,
					new ElGamalParameters(para.P, para.G));
			}
			else if (algOid.Equals(X9ObjectIdentifiers.IdDsa)
				|| algOid.Equals(OiwObjectIdentifiers.DsaWithSha1))
			{
				DerInteger derY = (DerInteger) keyInfo.GetPublicKey();
				Asn1Encodable ae = algID.Parameters;

				DsaParameters parameters = null;
				if (ae != null)
				{
					DsaParameter para = DsaParameter.GetInstance(ae.ToAsn1Object());
					parameters = new DsaParameters(para.P, para.Q, para.G);
				}

				return new DsaPublicKeyParameters(derY.Value, parameters);
			}
			else if (algOid.Equals(X9ObjectIdentifiers.IdECPublicKey))
			{
				X962Parameters para = new X962Parameters(
					algID.Parameters.ToAsn1Object());
				X9ECParameters ecP;

				if (para.IsNamedCurve)
				{
					ecP = ECKeyPairGenerator.FindECCurveByOid((DerObjectIdentifier)para.Parameters);
				}
				else
				{
					ecP = new X9ECParameters((Asn1Sequence)para.Parameters);
				}

				ECDomainParameters dParams = new ECDomainParameters(
					ecP.Curve,
					ecP.G,
					ecP.N,
					ecP.H,
					ecP.GetSeed());

				DerBitString bits = keyInfo.PublicKeyData;
				byte[] data = bits.GetBytes();
				Asn1OctetString key = new DerOctetString(data);

				X9ECPoint derQ = new X9ECPoint(dParams.Curve, key);

				return new ECPublicKeyParameters(derQ.Point, dParams);
			}
			else if (algOid.Equals(CryptoProObjectIdentifiers.GostR3410x2001))
			{
				Gost3410PublicKeyAlgParameters gostParams = new Gost3410PublicKeyAlgParameters(
					(Asn1Sequence) algID.Parameters);

				Asn1OctetString key;
				try
				{
					key = (Asn1OctetString) keyInfo.GetPublicKey();
				}
				catch (IOException)
				{
					throw new ArgumentException("invalid info structure in GOST3410 public key");
				}

				byte[] keyEnc = key.GetOctets();
				byte[] x = new byte[32];
				byte[] y = new byte[32];

				for (int i = 0; i != y.Length; i++)
				{
					x[i] = keyEnc[32 - 1 - i];
				}

				for (int i = 0; i != x.Length; i++)
				{
					y[i] = keyEnc[64 - 1 - i];
				}

				ECDomainParameters ecP = ECGost3410NamedCurves.GetByOid(gostParams.PublicKeyParamSet);

				if (ecP == null)
					return null;

				ECPoint q = ecP.Curve.CreatePoint(new BigInteger(1, x), new BigInteger(1, y), false);

				return new ECPublicKeyParameters("ECGOST3410", q, gostParams.PublicKeyParamSet);
			}
			else if (algOid.Equals(CryptoProObjectIdentifiers.GostR3410x94))
			{
				Gost3410PublicKeyAlgParameters algParams = new Gost3410PublicKeyAlgParameters(
					(Asn1Sequence) algID.Parameters);

				DerOctetString derY;
				try
				{
					derY = (DerOctetString) keyInfo.GetPublicKey();
				}
				catch (IOException)
				{
					throw new ArgumentException("invalid info structure in GOST3410 public key");
				}

				byte[] keyEnc = derY.GetOctets();
				byte[] keyBytes = new byte[keyEnc.Length];

				for (int i = 0; i != keyEnc.Length; i++)
				{
					keyBytes[i] = keyEnc[keyEnc.Length - 1 - i]; // was little endian
				}

				BigInteger y = new BigInteger(1, keyBytes);

				return new Gost3410PublicKeyParameters(y, algParams.PublicKeyParamSet);
			}
            else
            {
                throw new SecurityUtilityException("algorithm identifier in key not recognised: " + algOid);
            }
        }
		public static PrivateKeyInfo CreatePrivateKeyInfo(
			AsymmetricKeyParameter key)
		{
			if (key == null)
				throw new ArgumentNullException("key");
			if (!key.IsPrivate)
				throw new ArgumentException("Public key passed - private key expected", "key");

			if (key is ElGamalPrivateKeyParameters)
			{
				ElGamalPrivateKeyParameters _key = (ElGamalPrivateKeyParameters)key;
				return new PrivateKeyInfo(
					new AlgorithmIdentifier(
					OiwObjectIdentifiers.ElGamalAlgorithm,
					new ElGamalParameter(
					_key.Parameters.P,
					_key.Parameters.G).ToAsn1Object()),
					new DerInteger(_key.X));
			}

			if (key is DsaPrivateKeyParameters)
			{
				DsaPrivateKeyParameters _key = (DsaPrivateKeyParameters)key;
				return new PrivateKeyInfo(
					new AlgorithmIdentifier(
					X9ObjectIdentifiers.IdDsa,
					new DsaParameter(
					_key.Parameters.P,
					_key.Parameters.Q,
					_key.Parameters.G).ToAsn1Object()),
					new DerInteger(_key.X));
			}

			if (key is DHPrivateKeyParameters)
			{
				DHPrivateKeyParameters _key = (DHPrivateKeyParameters)key;

				DHParameter p = new DHParameter(
					_key.Parameters.P, _key.Parameters.G, _key.Parameters.L);

				return new PrivateKeyInfo(
					new AlgorithmIdentifier(_key.AlgorithmOid, p.ToAsn1Object()),
					new DerInteger(_key.X));
			}

			if (key is RsaKeyParameters)
			{
				AlgorithmIdentifier algID = new AlgorithmIdentifier(
					PkcsObjectIdentifiers.RsaEncryption, DerNull.Instance);

				RsaPrivateKeyStructure keyStruct;
				if (key is RsaPrivateCrtKeyParameters)
				{
					RsaPrivateCrtKeyParameters _key = (RsaPrivateCrtKeyParameters)key;

					keyStruct = new RsaPrivateKeyStructure(
						_key.Modulus,
						_key.PublicExponent,
						_key.Exponent,
						_key.P,
						_key.Q,
						_key.DP,
						_key.DQ,
						_key.QInv);
				}
				else
				{
					RsaKeyParameters _key = (RsaKeyParameters) key;

					keyStruct = new RsaPrivateKeyStructure(
						_key.Modulus,
						BigInteger.Zero,
						_key.Exponent,
						BigInteger.Zero,
						BigInteger.Zero,
						BigInteger.Zero,
						BigInteger.Zero,
						BigInteger.Zero);
				}

				return new PrivateKeyInfo(algID, keyStruct.ToAsn1Object());
			}

			if (key is ECPrivateKeyParameters)
			{
				ECPrivateKeyParameters _key = (ECPrivateKeyParameters)key;
				AlgorithmIdentifier algID;
				ECPrivateKeyStructure ec;

				if (_key.AlgorithmName == "ECGOST3410")
				{
					if (_key.PublicKeyParamSet == null)
						throw Platform.CreateNotImplementedException("Not a CryptoPro parameter set");

					Gost3410PublicKeyAlgParameters gostParams = new Gost3410PublicKeyAlgParameters(
						_key.PublicKeyParamSet, CryptoProObjectIdentifiers.GostR3411x94CryptoProParamSet);

					algID = new AlgorithmIdentifier(
						CryptoProObjectIdentifiers.GostR3410x2001,
						gostParams.ToAsn1Object());

					// TODO Do we need to pass any parameters here?
					ec = new ECPrivateKeyStructure(_key.D);
				}
				else
				{
					X962Parameters x962;
					if (_key.PublicKeyParamSet == null)
					{
						ECDomainParameters kp = _key.Parameters;
						X9ECParameters ecP = new X9ECParameters(kp.Curve, kp.G, kp.N, kp.H, kp.GetSeed());

						x962 = new X962Parameters(ecP);
					}
					else
					{
						x962 = new X962Parameters(_key.PublicKeyParamSet);
					}

					Asn1Object x962Object = x962.ToAsn1Object();

					// TODO Possible to pass the publicKey bitstring here?
					ec = new ECPrivateKeyStructure(_key.D, x962Object);

					algID = new AlgorithmIdentifier(X9ObjectIdentifiers.IdECPublicKey, x962Object);
				}

				return new PrivateKeyInfo(algID, ec.ToAsn1Object());
			}

			if (key is Gost3410PrivateKeyParameters)
			{
				Gost3410PrivateKeyParameters _key = (Gost3410PrivateKeyParameters)key;

				if (_key.PublicKeyParamSet == null)
					throw Platform.CreateNotImplementedException("Not a CryptoPro parameter set");

				byte[] keyEnc = _key.X.ToByteArrayUnsigned();
				byte[] keyBytes = new byte[keyEnc.Length];

				for (int i = 0; i != keyBytes.Length; i++)
				{
					keyBytes[i] = keyEnc[keyEnc.Length - 1 - i]; // must be little endian
				}

				Gost3410PublicKeyAlgParameters algParams = new Gost3410PublicKeyAlgParameters(
					_key.PublicKeyParamSet, CryptoProObjectIdentifiers.GostR3411x94CryptoProParamSet, null);

				AlgorithmIdentifier algID = new AlgorithmIdentifier(
					CryptoProObjectIdentifiers.GostR3410x94,
					algParams.ToAsn1Object());

				return new PrivateKeyInfo(algID, new DerOctetString(keyBytes));
			}

			throw new ArgumentException("Class provided is not convertible: " + key.GetType().FullName);
		}
		/// <summary>
        /// Create a Subject Public Key Info object for a given public key.
        /// </summary>
        /// <param name="key">One of ElGammalPublicKeyParameters, DSAPublicKeyParameter, DHPublicKeyParameters, RsaKeyParameters or ECPublicKeyParameters</param>
        /// <returns>A subject public key info object.</returns>
        /// <exception cref="Exception">Throw exception if object provided is not one of the above.</exception>
        public static SubjectPublicKeyInfo CreateSubjectPublicKeyInfo(
			AsymmetricKeyParameter key)
        {
			if (key == null)
				throw new ArgumentNullException("key");
            if (key.IsPrivate)
                throw new ArgumentException("Private key passed - public key expected.", "key");

			if (key is ElGamalPublicKeyParameters)
            {
				ElGamalPublicKeyParameters _key = (ElGamalPublicKeyParameters)key;
				ElGamalParameters kp = _key.Parameters;

				SubjectPublicKeyInfo info = new SubjectPublicKeyInfo(
					new AlgorithmIdentifier(
						OiwObjectIdentifiers.ElGamalAlgorithm,
						new ElGamalParameter(kp.P, kp.G).ToAsn1Object()),
						new DerInteger(_key.Y));

				return info;
            }

			if (key is DsaPublicKeyParameters)
            {
                DsaPublicKeyParameters _key = (DsaPublicKeyParameters) key;
				DsaParameters kp = _key.Parameters;
				Asn1Encodable ae = kp == null
					?	null
					:	new DsaParameter(kp.P, kp.Q, kp.G).ToAsn1Object();

				return new SubjectPublicKeyInfo(
                    new AlgorithmIdentifier(X9ObjectIdentifiers.IdDsa, ae),
					new DerInteger(_key.Y));
            }

			if (key is DHPublicKeyParameters)
            {
                DHPublicKeyParameters _key = (DHPublicKeyParameters) key;
				DHParameters kp = _key.Parameters;

				SubjectPublicKeyInfo info = new SubjectPublicKeyInfo(
                    new AlgorithmIdentifier(
						_key.AlgorithmOid,
						new DHParameter(kp.P, kp.G, kp.L).ToAsn1Object()),
						new DerInteger(_key.Y));

				return info;
            } // End of DH

            if (key is RsaKeyParameters)
            {
                RsaKeyParameters _key = (RsaKeyParameters) key;

				SubjectPublicKeyInfo info = new SubjectPublicKeyInfo(
					new AlgorithmIdentifier(PkcsObjectIdentifiers.RsaEncryption, DerNull.Instance),
					new RsaPublicKeyStructure(_key.Modulus, _key.Exponent).ToAsn1Object());

				return info;
            } // End of RSA.

			if (key is ECPublicKeyParameters)
            {
                ECPublicKeyParameters _key = (ECPublicKeyParameters) key;

				if (_key.AlgorithmName == "ECGOST3410")
				{
					if (_key.PublicKeyParamSet == null)
						throw Platform.CreateNotImplementedException("Not a CryptoPro parameter set");

					ECPoint q = _key.Q;
					BigInteger bX = q.X.ToBigInteger();
					BigInteger bY = q.Y.ToBigInteger();

					byte[] encKey = new byte[64];
					ExtractBytes(encKey, 0, bX);
					ExtractBytes(encKey, 32, bY);

					Gost3410PublicKeyAlgParameters gostParams = new Gost3410PublicKeyAlgParameters(
						_key.PublicKeyParamSet, CryptoProObjectIdentifiers.GostR3411x94CryptoProParamSet);

					AlgorithmIdentifier algID = new AlgorithmIdentifier(
						CryptoProObjectIdentifiers.GostR3410x2001,
						gostParams.ToAsn1Object());

					return new SubjectPublicKeyInfo(algID, new DerOctetString(encKey));
				}
				else
				{
					X962Parameters x962;
					if (_key.PublicKeyParamSet == null)
					{
						ECDomainParameters kp = _key.Parameters;
						X9ECParameters ecP = new X9ECParameters(kp.Curve, kp.G, kp.N, kp.H, kp.GetSeed());

						x962 = new X962Parameters(ecP);
					}
					else
					{
						x962 = new X962Parameters(_key.PublicKeyParamSet);
					}

					Asn1OctetString p = (Asn1OctetString)(new X9ECPoint(_key.Q).ToAsn1Object());

					AlgorithmIdentifier algID = new AlgorithmIdentifier(
						X9ObjectIdentifiers.IdECPublicKey, x962.ToAsn1Object());

					return new SubjectPublicKeyInfo(algID, p.GetOctets());
				}
			} // End of EC

			if (key is Gost3410PublicKeyParameters)
			{
				Gost3410PublicKeyParameters _key = (Gost3410PublicKeyParameters) key;

				if (_key.PublicKeyParamSet == null)
					throw Platform.CreateNotImplementedException("Not a CryptoPro parameter set");

				byte[] keyEnc = _key.Y.ToByteArrayUnsigned();
				byte[] keyBytes = new byte[keyEnc.Length];

				for (int i = 0; i != keyBytes.Length; i++)
				{
					keyBytes[i] = keyEnc[keyEnc.Length - 1 - i]; // must be little endian
				}

				Gost3410PublicKeyAlgParameters algParams = new Gost3410PublicKeyAlgParameters(
					_key.PublicKeyParamSet, CryptoProObjectIdentifiers.GostR3411x94CryptoProParamSet);

				AlgorithmIdentifier algID = new AlgorithmIdentifier(
					CryptoProObjectIdentifiers.GostR3410x94,
					algParams.ToAsn1Object());

				return new SubjectPublicKeyInfo(algID, new DerOctetString(keyBytes));
			}

			throw new ArgumentException("Class provided no convertible: " + key.GetType().FullName);
		}
		public static AsymmetricKeyParameter CreateKey(
			PrivateKeyInfo keyInfo)
        {
            AlgorithmIdentifier algID = keyInfo.AlgorithmID;
			DerObjectIdentifier algOid = algID.ObjectID;

			// TODO See RSAUtil.isRsaOid in Java build
			if (algOid.Equals(PkcsObjectIdentifiers.RsaEncryption)
				|| algOid.Equals(X509ObjectIdentifiers.IdEARsa)
				|| algOid.Equals(PkcsObjectIdentifiers.IdRsassaPss)
				|| algOid.Equals(PkcsObjectIdentifiers.IdRsaesOaep))
			{
				RsaPrivateKeyStructure keyStructure = new RsaPrivateKeyStructure(
					Asn1Sequence.GetInstance(keyInfo.PrivateKey));

				return new RsaPrivateCrtKeyParameters(
					keyStructure.Modulus,
					keyStructure.PublicExponent,
					keyStructure.PrivateExponent,
					keyStructure.Prime1,
					keyStructure.Prime2,
					keyStructure.Exponent1,
					keyStructure.Exponent2,
					keyStructure.Coefficient);
			}
			// TODO?
//			else if (algOid.Equals(X9ObjectIdentifiers.DHPublicNumber))
			else if (algOid.Equals(PkcsObjectIdentifiers.DhKeyAgreement))
			{
				DHParameter para = new DHParameter(
					Asn1Sequence.GetInstance(algID.Parameters.ToAsn1Object()));
				DerInteger derX = (DerInteger)keyInfo.PrivateKey;

				BigInteger lVal = para.L;
				int l = lVal == null ? 0 : lVal.IntValue;
				DHParameters dhParams = new DHParameters(para.P, para.G, null, l);

				return new DHPrivateKeyParameters(derX.Value, dhParams, algOid);
			}
			else if (algOid.Equals(OiwObjectIdentifiers.ElGamalAlgorithm))
			{
				ElGamalParameter  para = new ElGamalParameter(
					Asn1Sequence.GetInstance(algID.Parameters.ToAsn1Object()));
				DerInteger derX = (DerInteger)keyInfo.PrivateKey;

				return new ElGamalPrivateKeyParameters(
					derX.Value,
					new ElGamalParameters(para.P, para.G));
			}
			else if (algOid.Equals(X9ObjectIdentifiers.IdDsa))
			{
				DerInteger derX = (DerInteger) keyInfo.PrivateKey;
				Asn1Encodable ae = algID.Parameters;

				DsaParameters parameters = null;
				if (ae != null)
				{
					DsaParameter para = DsaParameter.GetInstance(ae.ToAsn1Object());
					parameters = new DsaParameters(para.P, para.Q, para.G);
				}

				return new DsaPrivateKeyParameters(derX.Value, parameters);
			}
			else if (algOid.Equals(X9ObjectIdentifiers.IdECPublicKey))
			{
				X962Parameters para = new X962Parameters(algID.Parameters.ToAsn1Object());
				X9ECParameters ecP;

				if (para.IsNamedCurve)
				{
					ecP = ECKeyPairGenerator.FindECCurveByOid((DerObjectIdentifier) para.Parameters);
				}
				else
				{
					ecP = new X9ECParameters((Asn1Sequence) para.Parameters);
				}

				ECDomainParameters dParams = new ECDomainParameters(
					ecP.Curve,
					ecP.G,
					ecP.N,
					ecP.H,
					ecP.GetSeed());

				ECPrivateKeyStructure ec = new ECPrivateKeyStructure(
					Asn1Sequence.GetInstance(keyInfo.PrivateKey));

				return new ECPrivateKeyParameters(ec.GetKey(), dParams);
			}
			else if (algOid.Equals(CryptoProObjectIdentifiers.GostR3410x2001))
			{
				Gost3410PublicKeyAlgParameters gostParams = new Gost3410PublicKeyAlgParameters(
					Asn1Sequence.GetInstance(algID.Parameters.ToAsn1Object()));

				ECPrivateKeyStructure ec = new ECPrivateKeyStructure(
					Asn1Sequence.GetInstance(keyInfo.PrivateKey));

				ECDomainParameters ecP = ECGost3410NamedCurves.GetByOid(gostParams.PublicKeyParamSet);

				if (ecP == null)
					return null;

				return new ECPrivateKeyParameters("ECGOST3410", ec.GetKey(), gostParams.PublicKeyParamSet);
			}
			else if (algOid.Equals(CryptoProObjectIdentifiers.GostR3410x94))
			{
				Gost3410PublicKeyAlgParameters gostParams = new Gost3410PublicKeyAlgParameters(
					Asn1Sequence.GetInstance(algID.Parameters.ToAsn1Object()));

				DerOctetString derX = (DerOctetString) keyInfo.PrivateKey;
				byte[] keyEnc = derX.GetOctets();
				byte[] keyBytes = new byte[keyEnc.Length];

				for (int i = 0; i != keyEnc.Length; i++)
				{
					keyBytes[i] = keyEnc[keyEnc.Length - 1 - i]; // was little endian
				}

				BigInteger x = new BigInteger(1, keyBytes);

				return new Gost3410PrivateKeyParameters(x, gostParams.PublicKeyParamSet);
			}
			else
			{
				throw new SecurityUtilityException("algorithm identifier in key not recognised");
			}
        }