How to fix "CCertRequest::Submit: The RPC server is unavailable. 0x800706ba" error?

Scenario:
I am learning AWS CloudHSM. So far, I have

• created an EC2 instance with Windows Server 2019 Datacenter as OS
• created a certification authority (root CA) on this server with Dintinguised Name "CN=myservername-CA1" (https://docs.aws.amazon.com/cloudhsm/latest/userguide/win-ca-setup.html )
• while connected to EC2 instance via RDP, I can login to my cloud hsm account and can manage users, create new keys etc.

Details of CA:

• Provider: RSA#Cavium Key Storage Provider
• Key Length: 2048
• Hash Algorithm: SHA256
• Distinguished Name: CN=myservername-CA1
• Cert Database log: C:\Windows\system32\CertLog

Now, I have developed a sample .Net WebAPI application which should send a CSR request to my CA and CA should return the signed certificate to the requester. This application is hosted as a web app on IIS on the same EC2 instance.

Source Code (https://blogs.msdn.microsoft.com/alejacma/2008/09/05/how-to-create-a-certificate-request-with-certenroll-and-net-c/ ):

using CloudHsmDemo.Models;
using System;
using System.Threading.Tasks;
using CERTENROLLLib;
using CERTCLILib;

namespace CloudHsmDemo.Services
{
    public interface ICertificateService
    {
        Task<CertificateSigningResponse> SignAsync(CertificateSigningRequest csr);
    }

    public class CertificateService : ICertificateService
    {
        private const int CC_DEFAULTCONFIG = 0;

        private const int CC_UIPICKCONFIG = 0x1;

        private const int CR_IN_BASE64 = 0x1;

        private const int CR_IN_FORMATANY = 0;

        private const int CR_IN_PKCS10 = 0x100;

        private const int CR_DISP_ISSUED = 0x3;

        private const int CR_DISP_UNDER_SUBMISSION = 0x5;

        private const int CR_OUT_BASE64 = 0x1;

        private const int CR_OUT_CHAIN = 0x100;

        public async Task<CertificateSigningResponse> SignAsync(CertificateSigningRequest csr)
        {
            if (csr.ShouldReturnDummyData)
            {
                return await DummySigningAsync(csr);
            }
            else
            {
                return await ActualSigningAsync(csr);
            }
        }

        private async Task<CertificateSigningResponse> DummySigningAsync(CertificateSigningRequest csr)
        {
            return PopulateCertificateSigningResponse("Sample Certificate", "Sample Message");
        }

        private async Task<CertificateSigningResponse> ActualSigningAsync(CertificateSigningRequest csr)
        {
            //  Create all the objects that will be required

            CCertConfig objCertConfig = new CCertConfigClass();

            CCertRequest objCertRequest = new CCertRequestClass();

            // string strCAConfig;

            string strRequest;

            int iDisposition;

            string strDisposition;

            string strCert;

            CertificateSigningResponse certificateSigningResponse;

            try

            {

                strRequest = await CreateCertificateSigningRequest(csr);


                // Get CA config from UI

                // strCAConfig = objCertConfig.GetConfig(CC_DEFAULTCONFIG);

                //strCAConfig = objCertConfig.GetConfig(CC_UIPICKCONFIG);


                // Submit the request

                iDisposition = objCertRequest.Submit(

                    CR_IN_BASE64 | CR_IN_FORMATANY,

                    strRequest,

                    null,

                    "<my_ec2_instance_public_dns>\\<my_server_name>"

                );

                // Check the submission status

                if (CR_DISP_ISSUED != iDisposition) // Not enrolled

                {

                    strDisposition = objCertRequest.GetDispositionMessage();


                    if (CR_DISP_UNDER_SUBMISSION == iDisposition) // Pending
                    {
                        certificateSigningResponse = PopulateCertificateSigningResponse(string.Empty, $"The submission is pending: {strDisposition}");
                    }

                    else // Failed

                    {
                        certificateSigningResponse = PopulateCertificateSigningResponse(string.Empty, $"The submission failed: {strDisposition}; Last Status: {objCertRequest.GetLastStatus().ToString()}");
                    }

                }


                // Get the certificate

                strCert = objCertRequest.GetCertificate(

                    CR_OUT_BASE64 | CR_OUT_CHAIN

                );


                certificateSigningResponse = PopulateCertificateSigningResponse(strCert, "Certificate signing process succeeded.");

            }

            catch (Exception ex)

            {

                certificateSigningResponse = PopulateCertificateSigningResponse(string.Empty, ex.Message);

            }
            if (certificateSigningResponse == null)
            {
                certificateSigningResponse = PopulateCertificateSigningResponse(string.Empty, "Certificate signing process failed.");
            }
            return certificateSigningResponse;
        }

        // this method creates a request string properly when 
        private async Task<string> CreateCertificateSigningRequest(CertificateSigningRequest csr)
        {
            //  Create all the objects that will be required

            CX509CertificateRequestPkcs10 objPkcs10 = new CX509CertificateRequestPkcs10Class();

            CX509PrivateKey objPrivateKey = new CX509PrivateKeyClass();

            CCspInformation objCSP = new CCspInformationClass();

            CCspInformations objCSPs = new CCspInformationsClass();

            CX500DistinguishedName objDN = new CX500DistinguishedNameClass();

            CX509Enrollment objEnroll = new CX509EnrollmentClass();

            CObjectIds objObjectIds = new CObjectIdsClass();

            CObjectId objObjectId = new CObjectIdClass();

            CX509ExtensionKeyUsage objExtensionKeyUsage = new CX509ExtensionKeyUsageClass();

            CX509ExtensionEnhancedKeyUsage objX509ExtensionEnhancedKeyUsage = new CX509ExtensionEnhancedKeyUsageClass();

            string strRequest;


            try

            {
                //  Initialize the csp object using the desired Cryptograhic Service Provider (CSP)

                objCSP.InitializeFromName("Microsoft Enhanced Cryptographic Provider v1.0");


                //objCSP.InitializeFromName("Cavium Key Storage Provider");

                //  Add this CSP object to the CSP collection object

                objCSPs.Add(objCSP);


                //  Provide key container name, key length and key spec to the private key object

                objPrivateKey.Length = csr.KeySize;

                objPrivateKey.KeySpec = X509KeySpec.XCN_AT_SIGNATURE;

                objPrivateKey.KeyUsage = X509PrivateKeyUsageFlags.XCN_NCRYPT_ALLOW_ALL_USAGES;

                objPrivateKey.MachineContext = false;


                //  Provide the CSP collection object (in this case containing only 1 CSP object)

                //  to the private key object

                objPrivateKey.CspInformations = objCSPs;


                //  Create the actual key pair
                objPrivateKey.Create();


                //  Initialize the PKCS#10 certificate request object based on the private key.

                //  Using the context, indicate that this is a user certificate request and don't

                //  provide a template name

                objPkcs10.InitializeFromPrivateKey(X509CertificateEnrollmentContext.ContextUser, objPrivateKey, "");


                // Key Usage Extension

                objExtensionKeyUsage.InitializeEncode(

                    X509KeyUsageFlags.XCN_CERT_DIGITAL_SIGNATURE_KEY_USAGE |

                    X509KeyUsageFlags.XCN_CERT_NON_REPUDIATION_KEY_USAGE |

                    X509KeyUsageFlags.XCN_CERT_KEY_ENCIPHERMENT_KEY_USAGE |

                    X509KeyUsageFlags.XCN_CERT_DATA_ENCIPHERMENT_KEY_USAGE

                );

                objPkcs10.X509Extensions.Add((CX509Extension)objExtensionKeyUsage);


                // Enhanced Key Usage Extension

                objObjectId.InitializeFromValue("1.3.6.1.5.5.7.3.2"); // OID for Client Authentication usage

                objObjectIds.Add(objObjectId);

                objX509ExtensionEnhancedKeyUsage.InitializeEncode(objObjectIds);

                objPkcs10.X509Extensions.Add((CX509Extension)objX509ExtensionEnhancedKeyUsage);


                //  Encode the name in using the Distinguished Name object

                objDN.Encode("CN=<myservername>-CA1", X500NameFlags.XCN_CERT_NAME_STR_NONE);


                //  Assing the subject name by using the Distinguished Name object initialized above

                objPkcs10.Subject = objDN;


                // Create enrollment request

                objEnroll.InitializeFromRequest(objPkcs10);

                strRequest = objEnroll.CreateRequest(

                    EncodingType.XCN_CRYPT_STRING_BASE64

                );
            }
            catch (Exception ex)
            {
                throw ex;
            }
            return strRequest;
        }

        private CertificateSigningResponse PopulateCertificateSigningResponse(string certificate, string message)
        {
            var responseObject = new CertificateSigningResponse
            {
                Certificate = certificate,
                Message = message,
                DateTimeInUTC = DateTime.UtcNow,
                Status = string.IsNullOrWhiteSpace(certificate) == true ? "Fail" : "Success"
            };
            return responseObject;
        }
    }
}

My sample JSON request:

{
    "CommonName":"My Test CSR",
    "Organization":"My Office",
    "OrganizationalUnit":"My Department",
    "CityOrLocality":"Sydney",
    "StateOrProvince":"NSW",
    "CountryOrRegion":"AU",
    "KeySize":2048,
    "ShouldReturnDummyData": false
}

Problem(s):

• when "Cavium Key Storage Provider" or "RSA#Cavium Key Storage Provider" is used to initialize objCSP, "Invalid provider specified. (Exception from HRESULT: 0x80090013)" exception is thrown

• when "Microsoft Enhanced Cryptographic Provider v1.0" is used to initialize objCSP, "CCertRequest::Submit: The RPC server is unavailable. 0x800706ba" exception is thrown

To resolve the "The RPC server is unavailable" issue, I have followed the steps https://itworldjd.wordpress.com/2015/10/21/pki-certificates-troubleshooting-certificate-enrollment-rpc-server-is-unavailable/ but no luck.

I hit this error too. Hopefully someone can benefit from how I addressed it.

After requesting a new cert over web enrollment I also got the error.

CCertRequest::Submit: The RPC server is unavailable. 0x800706ba (WIN32: 1722 RPC_S_SERVER_UNAVAILABLE)

Without going into all the detail of DCOM permissions you need to ensure you are accessing the Certificate web server remotely and not locally from the CA server.