protected string CheckSig()
        {
            var formData = Request.Form;
            var text = formData["txtSign"];
            var sig = formData["txtSig"];

            string output = "INVALID!";

            if (!string.IsNullOrEmpty(sig))
            {
                try
                {
                    ContentInfo contentInfo = new ContentInfo(Encoding.UTF8.GetBytes(text));

                    SignedCms signedCms = new SignedCms(contentInfo, true);

                    signedCms.Decode(Convert.FromBase64String(sig));

                    // This checks if the signature is valid, but doensn't actually verify the cert (TODO)
                    signedCms.CheckSignature(true);

                    output = "Signature valid.";

                    signedCms.CheckSignature(false);

                    output += "<br>Cert valid";
                }
                catch (Exception e)
                {
                    output += "<br>" + e.ToString();
                }
            }

            return output;
        }

        /// <summary> 
        /// Firma el mensaje PKCS #7 con el certificado del firmante
        /// </summary> 
        /// <param name="pMensaje">Mensaje (como cadena de bytes)</param> 
        /// <param name="pCertificadoFirmante">Certificado usado para firmar</param> 
        /// <returns>Mensaje Firmado (como cadena de bytes)</returns> 
        /// <remarks></remarks> 
        public static byte[] FirmarMensaje(byte[] pMensaje, X509Certificate2 pCertificadoFirmante)
        {
            byte[] msjFirmado;

            try
            {
                // Se pone el Mensaje recibido en un objeto ContentInfo                 
                ContentInfo infoContenidoMsj    = new ContentInfo(pMensaje);
                // Se instancia el CMS Firmado con el ContentInfo
                SignedCms cmsFirmado            = new SignedCms(infoContenidoMsj);
                // Se instancia el objeto CmsSigner con las caracteristicas del firmante 
                CmsSigner cmsFirmante = new CmsSigner(pCertificadoFirmante);

                cmsFirmante.IncludeOption = X509IncludeOption.EndCertOnly;

                // Se firma el mensaje PKCS #7 con el certificado
                cmsFirmado.ComputeSignature(cmsFirmante);

                msjFirmado = cmsFirmado.Encode();

                // Retorno el mensaje PKCS #7 firmado . 
                return msjFirmado;
            }
            catch (Exception excepcionAlFirmar)
            {
                throw new Exception("ERROR: Procedimiento: FirmarMensaje. Al intentar firmar el mensaje con el certificado del firmante: " + excepcionAlFirmar.Message);
            }
        }

        public bool ValidateToken(byte[] token, byte[] nonce, byte[] certificate, byte[] signature)
        {
            SignedCms cms = new SignedCms();
            cms.Decode(certificate);

            var certificates = cms.Certificates.Cast<X509Certificate2>().ToArray();

            var leaf = certificates.Single(cert => cert.Extensions.Cast<X509Extension>().Any(usage =>
            {
                var eku = usage as X509EnhancedKeyUsageExtension;
                if (eku != null)
                {
                    return eku.EnhancedKeyUsages.Cast<Oid>().Any(oid => oid.Value == "1.3.6.1.4.1.311.10.5.40");
                }
                return false;
            }));

            var signedData = nonce.Concat(token).ToArray();

            var publicKeyProvider = leaf.PublicKey.Key as System.Security.Cryptography.RSACryptoServiceProvider;

            return publicKeyProvider.VerifyData(signedData, CryptoConfig.MapNameToOID("SHA1"), signature);

            // not working either (same results)
            //
            //SHA1Managed hash = new SHA1Managed();
            //byte[] hashedData;
            //hashedData = hash.ComputeHash(signedData);

            //if (!publicKeyProvider.VerifyHash(hashedData, CryptoConfig.MapNameToOID("SHA1"), signature))
            //    throw new Exception("Invalid or Corrupted HardwareToken");
        }

		public void T1_ValidSignature ()
		{
			byte[] data = GetData ("SignedValidSignaturesTest1.eml");
			SignedCms cms = new SignedCms ();
			cms.Decode (data);
			Assert.IsTrue (CheckHash (cms), "CheckHash");
			Assert.IsTrue (CheckSignature (cms), "CheckSignature");

			X509Certificate2 ee = GetCertificate ("ValidCertificatePathTest1EE.crt");
			// certificates aren't in any particuliar order
			Assert.IsTrue (cms.Certificates.Contains (ee), "EE");
			Assert.IsTrue (cms.Certificates.Contains (GoodCACert), "GoodCACert");
			Assert.IsFalse (cms.Detached, "Detached");
			Assert.AreEqual (1, cms.Version, "Version");
			Assert.AreEqual ("1.2.840.113549.1.7.1", cms.ContentInfo.ContentType.Value, "ContentInfo.Oid");
			Assert.AreEqual ("43-6F-6E-74-65-6E-74-2D-54-79-70-65-3A-20-74-65-78-74-2F-70-6C-61-69-6E-3B-20-63-68-61-72-73-65-74-3D-69-73-6F-2D-38-38-35-39-2D-31-0D-0A-43-6F-6E-74-65-6E-74-2D-54-72-61-6E-73-66-65-72-2D-45-6E-63-6F-64-69-6E-67-3A-20-37-62-69-74-0D-0A-0D-0A-54-68-69-73-20-69-73-20-61-20-73-61-6D-70-6C-65-20-73-69-67-6E-65-64-20-6D-65-73-73-61-67-65-2E", BitConverter.ToString (cms.ContentInfo.Content), "ContentInfo.Content");
			Assert.AreEqual (1, cms.SignerInfos.Count, "SignerInfos.Count");
			Assert.AreEqual (ee, cms.SignerInfos[0].Certificate, "SignerInfos[0].Certificate");
			Assert.AreEqual (0, cms.SignerInfos[0].CounterSignerInfos.Count, "SignerInfos[0].CounterSignerInfos.Count");
			Assert.AreEqual ("1.3.14.3.2.26", cms.SignerInfos[0].DigestAlgorithm.Value, "cms.SignerInfos[0].DigestAlgorithm");
			Assert.AreEqual (0, cms.SignerInfos[0].SignedAttributes.Count, "SignerInfos[0].SignedAttributes.Count");
			Assert.AreEqual (SubjectIdentifierType.IssuerAndSerialNumber, cms.SignerInfos[0].SignerIdentifier.Type, "SignerInfos[0].SignerIdentifier.Type");
			X509IssuerSerial xis = (X509IssuerSerial) cms.SignerInfos[0].SignerIdentifier.Value;
			Assert.AreEqual ("CN=Good CA, O=Test Certificates, C=US", xis.IssuerName, "SignerInfos[0].SignerIdentifier.Value.IssuerName");
			Assert.AreEqual ("01", xis.SerialNumber, "SignerInfos[0].SignerIdentifier.Value.SerialNumber");
			Assert.AreEqual (0, cms.SignerInfos[0].UnsignedAttributes.Count, "SignerInfos[0].UnsignedAttributes.Count");
			Assert.AreEqual (1, cms.SignerInfos[0].Version, "SignerInfos[0].Version");
		}

		private void DefaultProperties (SignedCms sp, int version) 
		{
			// unaffected by constructors
			Assert.AreEqual (0, sp.Certificates.Count, "Certificates");
			Assert.AreEqual (0, sp.SignerInfos.Count, "SignerInfos");
			Assert.AreEqual (version, sp.Version, "Version");
		}

        /// <summary> 
        /// Firma mensaje 
        /// </summary> 
        /// <param name="argBytesMsg">Bytes del mensaje</param> 
        /// <param name="argCertFirmante">Certificado usado para firmar</param> 
        /// <returns>Bytes del mensaje firmado</returns> 
        /// <remarks></remarks> 
        public static byte[] FirmaBytesMensaje(byte[] argBytesMsg, X509Certificate2 argCertFirmante)
        {
            try
            {
                // Pongo el mensaje en un objeto ContentInfo (requerido para construir el obj SignedCms)
                ContentInfo infoContenido = new ContentInfo(argBytesMsg);
                SignedCms cmsFirmado = new SignedCms(infoContenido);

                // Creo objeto CmsSigner que tiene las caracteristicas del firmante
                CmsSigner cmsFirmante = new CmsSigner(argCertFirmante);
                cmsFirmante.IncludeOption = X509IncludeOption.EndCertOnly;

                if (VerboseMode)
                {
                    Console.WriteLine("***Firmando bytes del mensaje...");
                }
                // Firmo el mensaje PKCS #7
                cmsFirmado.ComputeSignature(cmsFirmante);

                if (VerboseMode)
                {
                    Console.WriteLine("***OK mensaje firmado");
                }

                // Encodeo el mensaje PKCS #7.
                return cmsFirmado.Encode();
            }
            catch (Exception excepcionAlFirmar)
            {
                throw new Exception("***Error al firmar: " + excepcionAlFirmar.Message);
            }
        }

 internal SignerInfo(SignedCms signedCms, System.Security.Cryptography.SafeLocalAllocHandle pbCmsgSignerInfo)
 {
     this.m_signedCms = signedCms;
     this.m_parentSignerInfo = null;
     this.m_encodedSignerInfo = null;
     this.m_pbCmsgSignerInfo = pbCmsgSignerInfo;
     this.m_cmsgSignerInfo = (System.Security.Cryptography.CAPI.CMSG_SIGNER_INFO) Marshal.PtrToStructure(pbCmsgSignerInfo.DangerousGetHandle(), typeof(System.Security.Cryptography.CAPI.CMSG_SIGNER_INFO));
 }

 public byte[] Sign(byte[] data)
 {
     ContentInfo contentInfo = new ContentInfo(_md5.ComputeHash(data));
     SignedCms signedCms = new SignedCms(contentInfo);
     CmsSigner cmsSigner = new CmsSigner(_cert);
     cmsSigner.IncludeOption = X509IncludeOption.WholeChain;
     signedCms.ComputeSignature(cmsSigner);
     return signedCms.Encode();
 }

        internal SignerInfo (SignedCms signedCms, SafeLocalAllocHandle pbCmsgSignerInfo) {
            // Sanity check.
            Debug.Assert(signedCms != null && pbCmsgSignerInfo != null && !pbCmsgSignerInfo.IsInvalid);

            m_signedCms = signedCms;
            m_parentSignerInfo = null;
            m_encodedSignerInfo = null;
            m_pbCmsgSignerInfo = pbCmsgSignerInfo;
            m_cmsgSignerInfo = (CAPI.CMSG_SIGNER_INFO) Marshal.PtrToStructure(pbCmsgSignerInfo.DangerousGetHandle(), typeof(CAPI.CMSG_SIGNER_INFO));
        }

        /// <summary>
        /// Gets certificates contained in pkcs 7.
        /// </summary>
        /// <returns>Returns certificates contained in pkcs 7. Returns null if no certificates.</returns>
        public X509Certificate2Collection GetCertificates()
        {
            if(this.Data == null){
                return null;
            }

            SignedCms signedCms = new SignedCms();
            signedCms.Decode(this.Data);

            return signedCms.Certificates;
        }

        public static void CheckSig(byte[] sig, byte[] data)
        {
            ContentInfo contentInfo = new ContentInfo(data);

            SignedCms signedCms = new SignedCms(contentInfo, true);

            signedCms.Decode(sig);

            // This checks if the signature is valid, but doensn't actually verify the cert (TODO)
            signedCms.CheckSignature(true);

            signedCms.CheckSignature(false);
        }

 public static bool VerifySign(byte[] data)
 {
     try
     {
         SignedCms signed = new SignedCms();
         signed.Decode(data);
     }
     catch
     {
         return false; // Arquivo não assinado
     }
     return true;
 }

 public bool Verify(byte[] data, byte[] signature)
 {
     var signedCms = new SignedCms();
     signedCms.Decode(signature);
     try
     {
         signedCms.CheckSignature(_certificate2Collection, false);
     }
     catch(Exception e)
     {
         return false;
     }
     return signedCms.ContentInfo.Content.SequenceEqual(_md5.ComputeHash(data));
 }

        /// <summary>
        /// Gets signed mime content. Value null means no content.
        /// </summary>
        /// <returns>Returns signed mime content. Value null means no content.</returns>
        /// <remarks>This method is valid only if <b>Content-Type</b> parameter <b>smime-type=signed-data</b>.</remarks>
        /// <exception cref="InvalidOperationException">Is raised when <b>smime-type != signed-data</b>.</exception>
        public MIME_Message GetSignedMime()
        {
            if(!string.Equals(this.Entity.ContentType.Parameters["smime-type"],"signed-data",StringComparison.InvariantCultureIgnoreCase)){
                throw new InvalidOperationException("The VerifySignature method is only valid if Content-Type parameter smime-type=signed-data.");
            }

            if(this.Data != null){
                SignedCms signedCms = new SignedCms();
                signedCms.Decode(this.Data);

                return MIME_Message.ParseFromStream(new MemoryStream(signedCms.ContentInfo.Content));
            }
            else{
                return null;
            }
        }

        public static String CheckFileSignature(ContentInfo content, byte[] signature)
        {
            var verifyCms = new SignedCms(content, true);
            verifyCms.Decode(signature);

            var cert = verifyCms.SignerInfos[0].Certificate;

            try
            {
                verifyCms.CheckSignature(new X509Certificate2Collection(cert), false);
                return @"Signature is valid";
            }
            catch (CryptographicException)
            {
                return @"Signature is not valid for content";
            }
        }

        private byte[] FirmaBytesMensaje( byte[] argBytesMsg, X509Certificate2 argCertFirmante )
        {
            ContentInfo infoContenido = new ContentInfo( argBytesMsg );
            SignedCms cmsFirmado = new SignedCms( infoContenido );
            CmsSigner cmsFirmante = new CmsSigner( argCertFirmante );

            try
            {
                cmsFirmante.IncludeOption = X509IncludeOption.EndCertOnly;
                cmsFirmado.ComputeSignature( cmsFirmante );

            }
            catch ( Exception error )
            {
                this.manejadorErrores.ManejarError( error, "FirmaBytesMensaje", error.Message );
            }
            return cmsFirmado.Encode();
        }

        public static bool IsSignedBy(this X509Certificate thisCertificate, X509Certificate signerCertificate)
        {
            X509Certificate2 c = new X509Certificate2(thisCertificate.GetTbsCertificate());
            X509Certificate2 i = new X509Certificate2(signerCertificate.GetTbsCertificate());
            X509Certificate2 c2 = new X509Certificate2(@"c:\temp\der.cer");
            X509Certificate2 i2 = new X509Certificate2(@"c:\temp\cader.cer");
            /*byte[] pvSubject = thisCertificate.GetTbsCertificate();
            byte[] pvIssuer = signerCertificate.GetTbsCertificate();
            */
            System.Text.Encoding.ASCII.GetString(c.RawData);
            IntPtr pvSubject = c.Handle;
            IntPtr pvIssuer = i.Handle;
            int res = SspiProvider.CryptVerifyCertificateSignatureEx(IntPtr.Zero, X509_ASN_ENCODING,
                                                           CRYPT_VERIFY_CERT_SIGN_SUBJECT_CERT, pvSubject,
                                                           CRYPT_VERIFY_CERT_SIGN_ISSUER_CERT, pvIssuer, 0,
                                                           IntPtr.Zero);
            Marshal.GetLastWin32Error();
            CmsSigner signer = new CmsSigner(i);
            SignedCms signedMessage = new SignedCms();
            // deserialize PKCS #7 byte array

            signedMessage.Decode(thisCertificate.GetTbsCertificate());
            Log.Write("Veryfy old");
            Log.Write("EndVeryfy old");
            Log.Write("Get signer's public key");
            var publicKey = signerCertificate.GetPublicKey();
            Log.Write("Got signer's public key");
            try
            {
                Log.Write("Veryfy signature");
                //TODO: log errors
                thisCertificate.Verify(publicKey);
                Log.Write("Verified");
            }
            catch (CertificateException)
            {
                return false;
            }
            catch (InvalidKeyException)
            {
                return false;
            }
            return true;
        }

        private MailMessage GenerateHtmlMessage(string from, string to, string subject, string content, string[] attachmentFilepaths)
        {
            MailMessage mail = new MailMessage();
            mail.From = new MailAddress(from);
            mail.To.Add(to);
            mail.Subject = subject;
            string body = null;
            if (attachmentFilepaths != null && attachmentFilepaths.Length > 0)
            {
                StringBuilder sb = new StringBuilder();
                sb.Append("MIME-Version: 1.0\r\n");
                sb.Append("Content-Type: multipart/mixed; boundary=unique-boundary-1\r\n");
                sb.Append("\r\n");
                sb.Append("This is a multi-part message in MIME format.\r\n");
                sb.Append("--unique-boundary-1\r\n");
                sb.Append("Content-Type: text/html\r\n");  //could use text/plain as well here if you want a plaintext message
                sb.Append("Content-Transfer-Encoding: 7Bit\r\n\r\n");
                sb.Append(content);
                if (!content.EndsWith("\r\n"))
                    sb.Append("\r\n");
                sb.Append("\r\n\r\n");
                foreach (string filepath in attachmentFilepaths)
                {
                    sb.Append(GenerateRawAttachement(filepath));
                }
                body = sb.ToString();
            }
            else
            {
                body = "Content-Type: text/html\r\nContent-Transfer-Encoding: 7Bit\r\n\r\n" + content;
            }
            //input your certification and private key.
            X509Certificate2 cert = new X509Certificate2("emailcertification.pfx", "6522626", X509KeyStorageFlags.Exportable | X509KeyStorageFlags.PersistKeySet);
            ContentInfo contentInfo = new ContentInfo(Encoding.UTF8.GetBytes(body));
            SignedCms signedCms = new SignedCms(contentInfo, false);
            CmsSigner Signer = new CmsSigner(SubjectIdentifierType.IssuerAndSerialNumber, cert);
            signedCms.ComputeSignature(Signer);
            byte[] signedBytes = signedCms.Encode();
            MemoryStream stream = new MemoryStream(signedBytes);
            AlternateView view = new AlternateView(stream, "application/pkcs7-mime; smime-type=signed-data;name=smime.p7m");
            mail.AlternateViews.Add(view);

            return mail;
        }

        /// <summary>
        /// 
        /// </summary>
        /// <param name="message"></param>
        /// <param name="signingCertificate"></param>
        /// <param name="encryptionCertificate"></param>
        /// <returns></returns>
        internal static byte[] GetSignature(Byte[] message, X509Certificate2 signingCertificate, X509Certificate2 encryptionCertificate)
        {
            SignedCms signedCms = new SignedCms(new ContentInfo(message), true);

            CmsSigner cmsSigner = new CmsSigner(SubjectIdentifierType.IssuerAndSerialNumber, signingCertificate);
            cmsSigner.IncludeOption = X509IncludeOption.WholeChain;

            if (encryptionCertificate != null)
            {
                cmsSigner.Certificates.Add(encryptionCertificate);
            }

            Pkcs9SigningTime signingTime = new Pkcs9SigningTime();
            cmsSigner.SignedAttributes.Add(signingTime);

            signedCms.ComputeSignature(cmsSigner, false);

            return signedCms.Encode();
        }

        public static SignatureResponse Sign(byte[] data)
        {
            // TODO:
            // padding configuration
            // algorithm configuration
            // encoding configuration
            /*
            SHA1Managed sha1 = new SHA1Managed();
            byte[] hash = sha1.ComputeHash(data);

            var sig = csp.SignHash(hash, CryptoConfig.MapNameToOID("SHA1"));
            //sig = csp.SignData(Encoding.UTF8.GetBytes(text), CryptoConfig.MapNameToOID("SHA1"));

            MessageBox.Show("SignData");
            */

            var content = new ContentInfo(data);
            var cms = new SignedCms(content, true); // TODO detached config
            var signer = new CmsSigner();
            signer.IncludeOption = X509IncludeOption.EndCertOnly;

            cms.ComputeSignature(signer, false);
            var sig = cms.Encode();

            //ensure my signature is correct before continuing.
            cms.CheckSignature(true);

            var newCMS = new SignedCms(content, false);
            newCMS.Decode(sig);
            newCMS.CheckSignature(true);

            var cert = cms.Certificates[0];
            CheckSig(sig, data);
            return new SignatureResponse
            {
                publicKey = Convert.ToBase64String(cert.PublicKey.EncodedKeyValue.RawData),
                signature = Convert.ToBase64String(sig),
                fullSig = null // TODO
            };
        }