/// <inheritdoc/>
        public async Task <X509CRLCollection> EnumerateCRLs(X509Certificate2 issuer, bool validateUpdateTime = true)
        {
            if (issuer == null)
            {
                throw new ArgumentNullException(nameof(issuer));
            }

            var crls = new X509CRLCollection();

            foreach (X509CRL crl in await EnumerateCRLs().ConfigureAwait(false))
            {
                if (!X509Utils.CompareDistinguishedName(crl.IssuerName, issuer.SubjectName))
                {
                    continue;
                }

                if (!crl.VerifySignature(issuer, false))
                {
                    continue;
                }

                if (!validateUpdateTime ||
                    crl.ThisUpdate <= DateTime.UtcNow && (crl.NextUpdate == DateTime.MinValue || crl.NextUpdate >= DateTime.UtcNow))
                {
                    crls.Add(crl);
                }
            }

            return(crls);
        }
Beispiel #2
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        /// <summary>
        /// Returns the CRLs for the issuer.
        /// </summary>
        public List <X509CRL> EnumerateCRLs(X509Certificate2 issuer, bool validateUpdateTime = true)
        {
            if (issuer == null)
            {
                throw new ArgumentNullException(nameof(issuer));
            }

            List <X509CRL> crls = new List <X509CRL>();

            foreach (X509CRL crl in EnumerateCRLs())
            {
                if (!X509Utils.CompareDistinguishedName(crl.Issuer, issuer.Subject))
                {
                    continue;
                }

                if (!crl.VerifySignature(issuer, false))
                {
                    continue;
                }

                if (!validateUpdateTime ||
                    crl.ThisUpdate <= DateTime.UtcNow && (crl.NextUpdate == DateTime.MinValue || crl.NextUpdate >= DateTime.UtcNow))
                {
                    crls.Add(crl);
                }
            }

            return(crls);
        }
Beispiel #3
0
        /// <summary>
        /// Finds a certificate in the specified collection.
        /// </summary>
        /// <param name="collection">The collection.</param>
        /// <param name="thumbprint">The thumbprint of the certificate.</param>
        /// <param name="subjectName">Subject name of the certificate.</param>
        /// <param name="needPrivateKey">if set to <c>true</c> [need private key].</param>
        /// <returns></returns>
        public static X509Certificate2 Find(X509Certificate2Collection collection, string thumbprint, string subjectName, bool needPrivateKey)
        {
            // find by thumbprint.
            if (!String.IsNullOrEmpty(thumbprint))
            {
                collection = collection.Find(X509FindType.FindByThumbprint, thumbprint, false);

                foreach (X509Certificate2 certificate in collection)
                {
                    if (!needPrivateKey || certificate.HasPrivateKey)
                    {
                        if (String.IsNullOrEmpty(subjectName))
                        {
                            return(certificate);
                        }

                        List <string> subjectName2 = X509Utils.ParseDistinguishedName(subjectName);

                        if (X509Utils.CompareDistinguishedName(certificate, subjectName2))
                        {
                            return(certificate);
                        }
                    }
                }

                return(null);
            }
            // find by subject name.
            if (!String.IsNullOrEmpty(subjectName))
            {
                List <string> subjectName2 = X509Utils.ParseDistinguishedName(subjectName);

                foreach (X509Certificate2 certificate in collection)
                {
                    if (X509Utils.CompareDistinguishedName(certificate, subjectName2))
                    {
                        if ((!needPrivateKey || certificate.HasPrivateKey) && X509Utils.GetRSAPublicKeySize(certificate) >= 0)
                        {
                            return(certificate);
                        }
                    }
                }

                collection = collection.Find(X509FindType.FindBySubjectName, subjectName, false);

                foreach (X509Certificate2 certificate in collection)
                {
                    if ((!needPrivateKey || certificate.HasPrivateKey) && X509Utils.GetRSAPublicKeySize(certificate) >= 0)
                    {
                        return(certificate);
                    }
                }
            }

            // certificate not found.
            return(null);
        }
        /// <summary>
        /// Returns the issuers for the certificates.
        /// </summary>
        public async Task <bool> GetIssuers(X509Certificate2Collection certificates, List <CertificateIdentifier> issuers)
        {
            bool isTrusted = false;
            CertificateIdentifier issuer      = null;
            X509Certificate2      certificate = certificates[0];

            CertificateIdentifierCollection collection = new CertificateIdentifierCollection();

            for (int ii = 1; ii < certificates.Count; ii++)
            {
                collection.Add(new CertificateIdentifier(certificates[ii]));
            }

            do
            {
                issuer = await GetIssuer(certificate, m_trustedCertificateList, m_trustedCertificateStore, true);

                if (issuer == null)
                {
                    issuer = await GetIssuer(certificate, m_issuerCertificateList, m_issuerCertificateStore, true);

                    if (issuer == null)
                    {
                        issuer = await GetIssuer(certificate, collection, null, true);
                    }
                }
                else
                {
                    isTrusted = true;
                }

                if (issuer != null)
                {
                    issuers.Add(issuer);
                    certificate = await issuer.Find(false);

                    // check for root.
                    if (X509Utils.CompareDistinguishedName(certificate.Subject, certificate.Issuer))
                    {
                        break;
                    }
                }
            }while (issuer != null);

            return(isTrusted);
        }
Beispiel #5
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        /// <summary>
        /// Adds a CRL to the store.
        /// </summary>
        public void AddCRL(X509CRL crl)
        {
            if (crl == null)
            {
                throw new ArgumentNullException(nameof(crl));
            }

            X509Certificate2           issuer       = null;
            X509Certificate2Collection certificates = null;

            certificates = Enumerate().Result;
            foreach (X509Certificate2 certificate in certificates)
            {
                if (X509Utils.CompareDistinguishedName(certificate.Subject, crl.Issuer))
                {
                    if (crl.VerifySignature(certificate, false))
                    {
                        issuer = certificate;
                        break;
                    }
                }
            }

            if (issuer == null)
            {
                throw new ServiceResultException(StatusCodes.BadCertificateInvalid, "Could not find issuer of the CRL.");
            }

            StringBuilder builder = new StringBuilder();

            builder.Append(m_directory.FullName);

            builder.Append(Path.DirectorySeparatorChar).Append("crl").Append(Path.DirectorySeparatorChar);
            builder.Append(GetFileName(issuer));
            builder.Append(".crl");

            FileInfo fileInfo = new FileInfo(builder.ToString());

            if (!fileInfo.Directory.Exists)
            {
                fileInfo.Directory.Create();
            }

            File.WriteAllBytes(fileInfo.FullName, crl.RawData);
        }
Beispiel #6
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        /// <summary>
        /// Get the certificate by issuer and serial number.
        /// </summary>
        public static async Task <X509Certificate2> FindIssuerCABySerialNumberAsync(
            ICertificateStore store,
            string issuer,
            string serialnumber)
        {
            X509Certificate2Collection certificates = await store.Enumerate();

            foreach (var certificate in certificates)
            {
                if (X509Utils.CompareDistinguishedName(certificate.Subject, issuer) &&
                    Utils.IsEqual(certificate.SerialNumber, serialnumber))
                {
                    return(certificate);
                }
            }

            return(null);
        }
        /// <summary>
        /// Returns true if the certificate matches the criteria.
        /// </summary>
        private bool Match(
            X509Certificate2 certificate,
            string subjectName,
            string serialNumber,
            string authorityKeyId)
        {
            // check for null.
            if (certificate == null)
            {
                return(false);
            }

            // check for subject name match.
            if (!X509Utils.CompareDistinguishedName(certificate.SubjectName.Name, subjectName))
            {
                return(false);
            }

            // check for serial number match.
            if (!String.IsNullOrEmpty(serialNumber))
            {
                if (certificate.SerialNumber != serialNumber)
                {
                    return(false);
                }
            }

            // check for authority key id match.
            if (!String.IsNullOrEmpty(authorityKeyId))
            {
                X509SubjectKeyIdentifierExtension subjectKeyId = X509Extensions.FindExtension <X509SubjectKeyIdentifierExtension>(certificate);

                if (subjectKeyId != null)
                {
                    if (subjectKeyId.SubjectKeyIdentifier != authorityKeyId)
                    {
                        return(false);
                    }
                }
            }

            // found match.
            return(true);
        }
Beispiel #8
0
        /// <summary>
        /// Checks if issuer has revoked the certificate.
        /// </summary>
        public StatusCode IsRevoked(X509Certificate2 issuer, X509Certificate2 certificate)
        {
            if (issuer == null)
            {
                throw new ArgumentNullException(nameof(issuer));
            }

            if (certificate == null)
            {
                throw new ArgumentNullException(nameof(certificate));
            }

            // check for CRL.
            DirectoryInfo info = new DirectoryInfo(this.Directory.FullName + Path.DirectorySeparatorChar + "crl");

            if (info.Exists)
            {
                bool crlExpired = true;

                foreach (FileInfo file in info.GetFiles("*.crl"))
                {
                    X509CRL crl = null;

                    try
                    {
                        crl = new X509CRL(file.FullName);
                    }
                    catch (Exception e)
                    {
                        Utils.LogError(e, "Could not parse CRL file.");
                        continue;
                    }

                    if (!X509Utils.CompareDistinguishedName(crl.Issuer, issuer.Subject))
                    {
                        continue;
                    }

                    if (!crl.VerifySignature(issuer, false))
                    {
                        continue;
                    }

                    if (crl.IsRevoked(certificate))
                    {
                        return(StatusCodes.BadCertificateRevoked);
                    }

                    if (crl.ThisUpdate <= DateTime.UtcNow && (crl.NextUpdate == DateTime.MinValue || crl.NextUpdate >= DateTime.UtcNow))
                    {
                        crlExpired = false;
                    }
                }

                // certificate is fine.
                if (!crlExpired)
                {
                    return(StatusCodes.Good);
                }
            }

            // can't find a valid CRL.
            return(StatusCodes.BadCertificateRevocationUnknown);
        }
Beispiel #9
0
        /// <summary>
        /// Loads the private key from a PFX file in the certificate store.
        /// </summary>
        public X509Certificate2 LoadPrivateKey(string thumbprint, string subjectName, string password)
        {
            if (m_certificateSubdir == null || !m_certificateSubdir.Exists)
            {
                return(null);
            }

            if (string.IsNullOrEmpty(thumbprint) && string.IsNullOrEmpty(subjectName))
            {
                return(null);
            }

            foreach (FileInfo file in m_certificateSubdir.GetFiles("*.der"))
            {
                try
                {
                    X509Certificate2 certificate = new X509Certificate2(file.FullName);

                    if (!String.IsNullOrEmpty(thumbprint))
                    {
                        if (!string.Equals(certificate.Thumbprint, thumbprint, StringComparison.CurrentCultureIgnoreCase))
                        {
                            continue;
                        }
                    }

                    if (!String.IsNullOrEmpty(subjectName))
                    {
                        if (!X509Utils.CompareDistinguishedName(subjectName, certificate.Subject))
                        {
                            if (subjectName.Contains('='))
                            {
                                continue;
                            }

                            if (!X509Utils.ParseDistinguishedName(certificate.Subject).Any(s => s.Equals("CN=" + subjectName, StringComparison.OrdinalIgnoreCase)))
                            {
                                continue;
                            }
                        }
                    }

                    // skip if not RSA certificate
                    if (X509Utils.GetRSAPublicKeySize(certificate) < 0)
                    {
                        continue;
                    }

                    string fileRoot = file.Name.Substring(0, file.Name.Length - file.Extension.Length);

                    StringBuilder filePath = new StringBuilder()
                                             .Append(m_privateKeySubdir.FullName)
                                             .Append(Path.DirectorySeparatorChar)
                                             .Append(fileRoot);

                    X509KeyStorageFlags[] storageFlags =
                    {
                        X509KeyStorageFlags.Exportable | X509KeyStorageFlags.MachineKeySet,
                        X509KeyStorageFlags.Exportable | X509KeyStorageFlags.UserKeySet
                    };

                    FileInfo privateKeyFile = new FileInfo(filePath.ToString() + ".pfx");
                    password = password ?? String.Empty;
                    foreach (var flag in storageFlags)
                    {
                        try
                        {
                            certificate = new X509Certificate2(
                                privateKeyFile.FullName,
                                password,
                                flag);
                            if (X509Utils.VerifyRSAKeyPair(certificate, certificate, true))
                            {
                                return(certificate);
                            }
                        }
                        catch (Exception)
                        {
                            certificate?.Dispose();
                            certificate = null;
                        }
                    }
                }
                catch (Exception e)
                {
                    Utils.LogError(e, "Could not load private key for certificate " + subjectName);
                }
            }

            return(null);
        }
 /// <summary>
 /// Check for self signed certificate if there is match of the Subject/Issuer.
 /// </summary>
 /// <param name="certificate">The certificate to test.</param>
 /// <returns>True if self signed.</returns>
 public static bool IsSelfSigned(X509Certificate2 certificate)
 {
     return(X509Utils.CompareDistinguishedName(certificate.SubjectName, certificate.IssuerName));
 }
        private static ServiceResult CheckChainStatus(X509ChainStatus status, CertificateIdentifier id, CertificateIdentifier issuer, bool isIssuer)
        {
            switch (status.Status)
            {
            case X509ChainStatusFlags.NotValidForUsage:
            {
                return(ServiceResult.Create(
                           (isIssuer) ? StatusCodes.BadCertificateUseNotAllowed : StatusCodes.BadCertificateIssuerUseNotAllowed,
                           "Certificate may not be used as an application instance certificate. {0}: {1}",
                           status.Status,
                           status.StatusInformation));
            }

            case X509ChainStatusFlags.NoError:
            case X509ChainStatusFlags.OfflineRevocation:
            case X509ChainStatusFlags.InvalidBasicConstraints:
            {
                break;
            }

            case X509ChainStatusFlags.PartialChain:
            case X509ChainStatusFlags.UntrustedRoot:
            {
                // self signed cert signature validation
                // .Net Core ChainStatus returns NotSignatureValid only on Windows,
                // so we have to do the extra cert signature check on all platforms
                if (issuer == null && !isIssuer &&
                    id.Certificate != null && X509Utils.CompareDistinguishedName(id.Certificate.Subject, id.Certificate.Issuer))
                {
                    if (!IsSignatureValid(id.Certificate))
                    {
                        goto case X509ChainStatusFlags.NotSignatureValid;
                    }
                }

                // ignore this error because the root check is done
                // by looking the certificate up in the trusted issuer stores passed to the validator.
                // the ChainStatus uses the trusted issuer stores.
                break;
            }

            case X509ChainStatusFlags.RevocationStatusUnknown:
            {
                if (issuer != null)
                {
                    if ((issuer.ValidationOptions & CertificateValidationOptions.SuppressRevocationStatusUnknown) != 0)
                    {
                        break;
                    }
                }

                // check for meaning less errors for self-signed certificates.
                if (id.Certificate != null && X509Utils.CompareDistinguishedName(id.Certificate.Subject, id.Certificate.Subject))
                {
                    break;
                }

                return(ServiceResult.Create(
                           (isIssuer) ? StatusCodes.BadCertificateIssuerRevocationUnknown : StatusCodes.BadCertificateRevocationUnknown,
                           "Certificate revocation status cannot be verified. {0}: {1}",
                           status.Status,
                           status.StatusInformation));
            }

            case X509ChainStatusFlags.Revoked:
            {
                return(ServiceResult.Create(
                           (isIssuer) ? StatusCodes.BadCertificateIssuerRevoked : StatusCodes.BadCertificateRevoked,
                           "Certificate has been revoked. {0}: {1}",
                           status.Status,
                           status.StatusInformation));
            }

            case X509ChainStatusFlags.NotTimeNested:
            {
                if (id != null && ((id.ValidationOptions & CertificateValidationOptions.SuppressCertificateExpired) != 0))
                {
                    // TODO: add logging
                    break;
                }

                return(ServiceResult.Create(
                           StatusCodes.BadCertificateIssuerTimeInvalid,
                           "Issuer Certificate has expired or is not yet valid. {0}: {1}",
                           status.Status,
                           status.StatusInformation));
            }

            case X509ChainStatusFlags.NotTimeValid:
            {
                if (id != null && ((id.ValidationOptions & CertificateValidationOptions.SuppressCertificateExpired) != 0))
                {
                    // TODO: add logging
                    break;
                }

                return(ServiceResult.Create(
                           (isIssuer) ? StatusCodes.BadCertificateIssuerTimeInvalid : StatusCodes.BadCertificateTimeInvalid,
                           "Certificate has expired or is not yet valid. {0}: {1}",
                           status.Status,
                           status.StatusInformation));
            }

            case X509ChainStatusFlags.NotSignatureValid:
            default:
            {
                return(ServiceResult.Create(
                           StatusCodes.BadCertificateInvalid,
                           "Certificate validation failed. {0}: {1}",
                           status.Status,
                           status.StatusInformation));
            }
            }

            return(null);
        }
        /// <summary>
        /// Throws an exception if validation fails.
        /// </summary>
        /// <param name="certificates">The certificates to be checked.</param>
        /// <exception cref="ServiceResultException">If certificate[0] cannot be accepted</exception>
        protected virtual async Task InternalValidate(X509Certificate2Collection certificates)
        {
            X509Certificate2 certificate = certificates[0];

            // check for previously validated certificate.
            X509Certificate2 certificate2 = null;

            if (m_validatedCertificates.TryGetValue(certificate.Thumbprint, out certificate2))
            {
                if (Utils.IsEqual(certificate2.RawData, certificate.RawData))
                {
                    return;
                }
            }

            CertificateIdentifier trustedCertificate = await GetTrustedCertificate(certificate);

            // get the issuers (checks the revocation lists if using directory stores).
            List <CertificateIdentifier> issuers = new List <CertificateIdentifier>();
            bool isIssuerTrusted = await GetIssuers(certificates, issuers);

            // setup policy chain
            X509ChainPolicy policy = new X509ChainPolicy();

            policy.RevocationFlag    = X509RevocationFlag.EntireChain;
            policy.RevocationMode    = X509RevocationMode.NoCheck;
            policy.VerificationFlags = X509VerificationFlags.NoFlag;

            foreach (CertificateIdentifier issuer in issuers)
            {
                if ((issuer.ValidationOptions & CertificateValidationOptions.SuppressRevocationStatusUnknown) != 0)
                {
                    policy.VerificationFlags |= X509VerificationFlags.IgnoreCertificateAuthorityRevocationUnknown;
                    policy.VerificationFlags |= X509VerificationFlags.IgnoreCtlSignerRevocationUnknown;
                    policy.VerificationFlags |= X509VerificationFlags.IgnoreEndRevocationUnknown;
                    policy.VerificationFlags |= X509VerificationFlags.IgnoreRootRevocationUnknown;
                }

                // we did the revocation check in the GetIssuers call. No need here.
                policy.RevocationMode = X509RevocationMode.NoCheck;
                policy.ExtraStore.Add(issuer.Certificate);
            }

            // build chain.
            X509Chain chain = new X509Chain();

            chain.ChainPolicy = policy;
            chain.Build(certificate);

            // check the chain results.
            CertificateIdentifier target = trustedCertificate;

            if (target == null)
            {
                target = new CertificateIdentifier(certificate);
            }

            ServiceResult sresult = null;

            for (int ii = 0; ii < chain.ChainElements.Count; ii++)
            {
                X509ChainElement element = chain.ChainElements[ii];

                CertificateIdentifier issuer = null;

                if (ii < issuers.Count)
                {
                    issuer = issuers[ii];
                }
                // check for chain status errors.
                if (element.ChainElementStatus.Length > 0)
                {
                    foreach (X509ChainStatus status in element.ChainElementStatus)
                    {
                        ServiceResult result = CheckChainStatus(status, target, issuer, (ii != 0));
                        if (ServiceResult.IsBad(result))
                        {
                            sresult = new ServiceResult(result, sresult);
                        }
                    }
                }

                if (issuer != null)
                {
                    target = issuer;
                }
            }

            // check whether the chain is complete (if there is a chain)
            bool issuedByCA      = !X509Utils.CompareDistinguishedName(certificate.Subject, certificate.Issuer);
            bool chainIncomplete = false;

            if (issuers.Count > 0)
            {
                var rootCertificate = issuers[issuers.Count - 1].Certificate;
                if (!X509Utils.CompareDistinguishedName(rootCertificate.Subject, rootCertificate.Issuer))
                {
                    chainIncomplete = true;
                }
            }
            else
            {
                if (issuedByCA)
                {
                    // no issuer found at all
                    chainIncomplete = true;
                }
            }

            // check if certificate issuer is trusted.
            if (issuedByCA && !isIssuerTrusted && trustedCertificate == null)
            {
                var message = CertificateMessage("Certificate issuer is not trusted.", certificate);
                sresult = new ServiceResult(StatusCodes.BadCertificateUntrusted,
                                            null,
                                            null,
                                            message,
                                            null,
                                            sresult
                                            );
            }

            // check if certificate is trusted.
            if (trustedCertificate == null && !isIssuerTrusted)
            {
                if (m_applicationCertificate == null || !Utils.IsEqual(m_applicationCertificate.RawData, certificate.RawData))
                {
                    var message = CertificateMessage("Certificate is not trusted.", certificate);
                    sresult = new ServiceResult(StatusCodes.BadCertificateUntrusted,
                                                null,
                                                null,
                                                message,
                                                null,
                                                sresult
                                                );
                }
            }

            // check if certificate is valid for use as app/sw or user cert
            X509KeyUsageFlags certificateKeyUsage = X509Utils.GetKeyUsage(certificate);

            if ((certificateKeyUsage & X509KeyUsageFlags.DataEncipherment) == 0)
            {
                sresult = new ServiceResult(StatusCodes.BadCertificateUseNotAllowed,
                                            null,
                                            null,
                                            "Usage of certificate is not allowed.",
                                            null,
                                            sresult
                                            );
            }

            // check if minimum requirements are met
            if (m_rejectSHA1SignedCertificates && IsSHA1SignatureAlgorithm(certificate.SignatureAlgorithm))
            {
                sresult = new ServiceResult(StatusCodes.BadCertificatePolicyCheckFailed,
                                            null,
                                            null,
                                            "SHA1 signed certificates are not trusted.",
                                            null,
                                            sresult
                                            );
            }

            int keySize = X509Utils.GetRSAPublicKeySize(certificate);

            if (keySize < m_minimumCertificateKeySize)
            {
                sresult = new ServiceResult(StatusCodes.BadCertificatePolicyCheckFailed,
                                            null,
                                            null,
                                            "Certificate doesn't meet minimum key length requirement.",
                                            null,
                                            sresult
                                            );
            }

            if (issuedByCA && chainIncomplete)
            {
                var message = CertificateMessage("Certificate chain validation incomplete.", certificate);
                sresult = new ServiceResult(StatusCodes.BadCertificateChainIncomplete,
                                            null, null, message, null, sresult);
            }
            if (sresult != null)
            {
                throw new ServiceResultException(sresult);
            }
        }
        /// <summary>
        /// Returns the certificate information for a trusted issuer certificate.
        /// </summary>
        private async Task <CertificateIdentifier> GetIssuer(
            X509Certificate2 certificate,
            CertificateIdentifierCollection explicitList,
            CertificateStoreIdentifier certificateStore,
            bool checkRecovationStatus)
        {
            // check if self-signed.
            if (X509Utils.CompareDistinguishedName(certificate.Subject, certificate.Issuer))
            {
                return(null);
            }

            string subjectName  = certificate.IssuerName.Name;
            string keyId        = null;
            string serialNumber = null;

            // find the authority key identifier.
            X509AuthorityKeyIdentifierExtension authority = X509Extensions.FindExtension <X509AuthorityKeyIdentifierExtension>(certificate);

            if (authority != null)
            {
                keyId        = authority.KeyIdentifier;
                serialNumber = authority.SerialNumber;
            }

            // check in explicit list.
            if (explicitList != null)
            {
                for (int ii = 0; ii < explicitList.Count; ii++)
                {
                    X509Certificate2 issuer = await explicitList[ii].Find(false);

                    if (issuer != null)
                    {
                        if (!X509Utils.IsIssuerAllowed(issuer))
                        {
                            continue;
                        }

                        if (Match(issuer, subjectName, serialNumber, keyId))
                        {
                            // can't check revocation.
                            return(new CertificateIdentifier(issuer, CertificateValidationOptions.SuppressRevocationStatusUnknown));
                        }
                    }
                }
            }

            // check in certificate store.
            if (certificateStore != null)
            {
                ICertificateStore store = certificateStore.OpenStore();

                try
                {
                    X509Certificate2Collection certificates = await store.Enumerate();

                    for (int ii = 0; ii < certificates.Count; ii++)
                    {
                        X509Certificate2 issuer = certificates[ii];

                        if (issuer != null)
                        {
                            if (!X509Utils.IsIssuerAllowed(issuer))
                            {
                                continue;
                            }

                            if (Match(issuer, subjectName, serialNumber, keyId))
                            {
                                CertificateValidationOptions options = certificateStore.ValidationOptions;

                                // already checked revocation for file based stores. windows based stores always suppress.
                                options |= CertificateValidationOptions.SuppressRevocationStatusUnknown;

                                if (checkRecovationStatus)
                                {
                                    StatusCode status = store.IsRevoked(issuer, certificate);

                                    if (StatusCode.IsBad(status) && status != StatusCodes.BadNotSupported)
                                    {
                                        if (status == StatusCodes.BadCertificateRevocationUnknown)
                                        {
                                            if (X509Utils.IsCertificateAuthority(certificate))
                                            {
                                                status.Code = StatusCodes.BadCertificateIssuerRevocationUnknown;
                                            }

                                            if (m_rejectUnknownRevocationStatus)
                                            {
                                                throw new ServiceResultException(status);
                                            }
                                        }
                                        else
                                        {
                                            throw new ServiceResultException(status);
                                        }
                                    }
                                }

                                return(new CertificateIdentifier(certificates[ii], options));
                            }
                        }
                    }
                }
                finally
                {
                    store.Close();
                }
            }

            // not a trusted issuer.
            return(null);
        }
        /// <summary>
        /// Loads the private key from a PFX/PEM file in the certificate store.
        /// </summary>
        public async Task <X509Certificate2> LoadPrivateKey(string thumbprint, string subjectName, string password)
        {
            if (NoPrivateKeys || m_certificateSubdir == null || !m_certificateSubdir.Exists)
            {
                return(null);
            }

            if (string.IsNullOrEmpty(thumbprint) && string.IsNullOrEmpty(subjectName))
            {
                return(null);
            }

            // on some platforms, specifically in virtualized environments,
            // reloading a previously created and saved private key may fail on the first attempt.
            const int retryDelay   = 100;
            int       retryCounter = 3;

            while (retryCounter-- > 0)
            {
                bool      certificateFound = false;
                Exception importException  = null;
                foreach (FileInfo file in m_certificateSubdir.GetFiles("*.der"))
                {
                    try
                    {
                        X509Certificate2 certificate = new X509Certificate2(file.FullName);

                        if (!String.IsNullOrEmpty(thumbprint))
                        {
                            if (!string.Equals(certificate.Thumbprint, thumbprint, StringComparison.OrdinalIgnoreCase))
                            {
                                continue;
                            }
                        }

                        if (!String.IsNullOrEmpty(subjectName))
                        {
                            if (!X509Utils.CompareDistinguishedName(subjectName, certificate.Subject))
                            {
                                if (subjectName.Contains('='))
                                {
                                    continue;
                                }

                                if (!X509Utils.ParseDistinguishedName(certificate.Subject).Any(s => s.Equals("CN=" + subjectName, StringComparison.Ordinal)))
                                {
                                    continue;
                                }
                            }
                        }

                        // skip if not RSA certificate
                        if (X509Utils.GetRSAPublicKeySize(certificate) < 0)
                        {
                            continue;
                        }

                        string fileRoot = file.Name.Substring(0, file.Name.Length - file.Extension.Length);

                        StringBuilder filePath = new StringBuilder()
                                                 .Append(m_privateKeySubdir.FullName)
                                                 .Append(Path.DirectorySeparatorChar)
                                                 .Append(fileRoot);

                        X509KeyStorageFlags[] storageFlags =
                        {
                            X509KeyStorageFlags.Exportable | X509KeyStorageFlags.MachineKeySet,
                            X509KeyStorageFlags.Exportable | X509KeyStorageFlags.UserKeySet
                        };

                        FileInfo privateKeyFilePfx = new FileInfo(filePath + ".pfx");
                        FileInfo privateKeyFilePem = new FileInfo(filePath + ".pem");
                        password = password ?? String.Empty;
                        if (privateKeyFilePfx.Exists)
                        {
                            certificateFound = true;
                            foreach (var flag in storageFlags)
                            {
                                try
                                {
                                    certificate = new X509Certificate2(
                                        privateKeyFilePfx.FullName,
                                        password,
                                        flag);
                                    if (X509Utils.VerifyRSAKeyPair(certificate, certificate, true))
                                    {
                                        Utils.LogInfo(Utils.TraceMasks.Security, "Imported the PFX private key for [{0}].", certificate.Thumbprint);
                                        return(certificate);
                                    }
                                }
                                catch (Exception ex)
                                {
                                    importException = ex;
                                    certificate?.Dispose();
                                }
                            }
                        }
                        // if PFX file doesn't exist, check for PEM file.
                        else if (privateKeyFilePem.Exists)
                        {
                            certificateFound = true;
                            try
                            {
                                byte[] pemDataBlob = File.ReadAllBytes(privateKeyFilePem.FullName);
                                certificate = CertificateFactory.CreateCertificateWithPEMPrivateKey(certificate, pemDataBlob, password);
                                if (X509Utils.VerifyRSAKeyPair(certificate, certificate, true))
                                {
                                    Utils.LogInfo(Utils.TraceMasks.Security, "Imported the PEM private key for [{0}].", certificate.Thumbprint);
                                    return(certificate);
                                }
                            }
                            catch (Exception exception)
                            {
                                certificate?.Dispose();
                                importException = exception;
                            }
                        }
                        else
                        {
                            Utils.LogError(Utils.TraceMasks.Security, "A private key for the certificate with thumbprint [{0}] does not exist.", certificate.Thumbprint);
                            continue;
                        }
                    }
                    catch (Exception e)
                    {
                        Utils.LogError(e, "Could not load private key for certificate {0}", subjectName);
                    }
                }

                // found a certificate, but some error occurred
                if (certificateFound)
                {
                    Utils.LogError(Utils.TraceMasks.Security, "The private key for the certificate with subject {0} failed to import.", subjectName);
                    if (importException != null)
                    {
                        Utils.LogError(importException, "Certificate import failed.");
                    }
                }
                else
                {
                    if (!String.IsNullOrEmpty(thumbprint))
                    {
                        Utils.LogError(Utils.TraceMasks.Security, "A Private key for the certificate with thumbpint {0} was not found.", thumbprint);
                    }
                    // if no private key was found, no need to retry
                    break;
                }

                // retry within a few ms
                if (retryCounter > 0)
                {
                    Utils.LogInfo(Utils.TraceMasks.Security, "Retry to import private key after {0} ms.", retryDelay);
                    await Task.Delay(retryDelay).ConfigureAwait(false);
                }
            }

            return(null);
        }