ODP: CSR creation using pkcs11 dynamic engine

Fri May 28 17:43:41 UTC 2021

Ok, i have found out that dotnet OpenSsl library has it's own code for verification is key private. For this it needs the whole data of private key from which this method:

static int HasNoPrivateKey(RSA* rsa)

 which is in ./src/Native/Unix/System.Security.Cryptography.Native/pal_rsa.c of dotnet verifies occurence of all private parameters. Unfortunately from what i know private keys are not extractable from tokens because of CKA_EXTRACTABLE=false parameter.

Correct me if i'm wrong but from what i know about openssl, when i'm switching to a closed engine the whole cryptography is being made by the engine module. I think that there should be some other method verifing if key is private. Maybe somebody could give me a hint?

BR
Piotr
________________________________
Od: openssl-users <openssl-users-bounces at openssl.org> w imieniu użytkownika Piotr Lobacz <piotr.lobacz at softgent.com>
Wysłane: piątek, 28 maja 2021 13:10
Do: openssl-users at openssl.org <openssl-users at openssl.org>
Temat: CSR creation using pkcs11 dynamic engine

Hi all,
i'm trying to generate CSR using C# System.SecurityCryptography.Openssl library together with pkcs11 token library. The whole proces for this in command line works without any problems. For execution of this process i use command:

openssl req -new -subj '/C=PL/ST=Gdansk/L=Gdansk/CN=softgent.com/' -sha256 -engine pkcs11 -keyform engine -key "pkcs11:token=foo;object=tls;type=private;pin-value=1234567890"

The CSR is being generated and the output is like this:

Now i'm trying to do all that programatically. In order to do that i have added some OpenSsl C# missing support for the engines and used the ENGINE_load_private_key method to retrieve SafeEvpPKeyHandle which is being retrieved (i have checked it with changing the key id value). The key which i'm using is "label_" + myKeyId i.e. "label_tls". The code looks like this:

public virtual SafeEvpPKeyHandle GetPrivKey(string label)
{
    string keyId = "label_" + label;
    SafeEvpPKeyHandle pkey = SafeNativeMethods.ENGINE_load_private_key(engine, keyId, IntPtr.Zero, IntPtr.Zero);
    if(pkey.IsInvalid)
    {
         throw new InvalidOperationException("engine: unable to find private key with label='{label}'");
    }

    return pkey;
}

This is being returnin me SafeEvpPKeyHandle. The problem is in calling CreateSigningRequest from System.Security.Cryptography.OpenSsl.dll. I have this method:

public virtual string GetCSR(SafeEvpPKeyHandle pkey, string ext, HashAlgorithmName name)
{
    // FIXME: determine key type
    RSA rsa = new RSAOpenSsl(pkey);

    CertificateRequest req = new CertificateRequest("CN=potato", rsa, name, RSASignaturePadding.Pkcs1); // this method is only for RSA key different is for EC, DSA etc.
    byte[] requestDer = req.CreateSigningRequest();
    string requestPem = new string(PemEncoding.Write("CERTIFICATE REQUEST", requestDer));
    return requestPem;
}

and i'm getting this error:

Unhandled exception. Interop+Crypto+OpenSslCryptographicException: error:04075093:rsa routines:RSA_sign:value missing
   at System.Security.Cryptography.RSAOpenSsl.TrySignHash(ReadOnlySpan`1 hash, Span`1 destination, HashAlgorithmName hashAlgorithm, RSASignaturePadding padding, Boolean allocateSignature, Int32& bytesWritten, Byte[]& signature)
   at System.Security.Cryptography.RSAOpenSsl.SignHash(Byte[] hash, HashAlgorithmName hashAlgorithm, RSASignaturePadding padding)
   at System.Security.Cryptography.RSA.SignData(Byte[] data, Int32 offset, Int32 count, HashAlgorithmName hashAlgorithm, RSASignaturePadding padding)
   at System.Security.Cryptography.RSA.SignData(Byte[] data, HashAlgorithmName hashAlgorithm, RSASignaturePadding padding)
   at System.Security.Cryptography.X509Certificates.RSAPkcs1X509SignatureGenerator.SignData(Byte[] data, HashAlgorithmName hashAlgorithm)
   at System.Security.Cryptography.X509Certificates.Pkcs10CertificationRequestInfo.ToPkcs10Request(X509SignatureGenerator signatureGenerator, HashAlgorithmName hashAlgorithm)
   at System.Security.Cryptography.X509Certificates.CertificateRequest.CreateSigningRequest(X509SignatureGenerator signatureGenerator)
   at System.Security.Cryptography.X509Certificates.CertificateRequest.CreateSigningRequest()
   at System.Security.Cryptography.Engine.GetCSR(SafeEvpPKeyHandle pkey, String ext, HashAlgorithmName name) in /home/plobacz/workspace/OpenSsl.DynamicEngine/Engine.cs:line 72
   at Flexgent.Services.CryptoSubsystem.CryptoSubsystem.Configure(String config) in /home/plobacz/workspace/crypto-subsystem/flexgent/extensions/security/crypto-subsystem/src/CryptoSubsystem.cs:line 145
   at Flexgent.Core.Service.Flexgent.Core.IService.Configure(String config) in /home/plobacz/workspace/crypto-subsystem/flexgent/core/library/src/Classes/Service.cs:line 42
   at Flexgent.Core.ServiceRunner`1.Run(ServiceRunnerOptions options, Action`1 mainLoop, IEnumerable`1 standaloneConnectInterfaces) in /home/plobacz/workspace/crypto-subsystem/flexgent/core/library/src/Classes/ServiceRunner.cs:line 50
   at Flexgent.Services.CryptoSubsystem.CryptoSubsystemMain.<>c.<Main>b__1_0(ServiceRunnerOptions o) in /home/plobacz/workspace/crypto-subsystem/flexgent/extensions/security/crypto-subsystem/src/ServiceMain.cs:line 20
   at CommandLine.ParserResultExtensions.WithParsed[T](ParserResult`1 result, Action`1 action)
   at Flexgent.Services.CryptoSubsystem.CryptoSubsystemMain.Main(String[] args) in /home/plobacz/workspace/crypto-subsystem/flexgent/extensions/security/crypto-subsystem/src/ServiceMain.cs:line 19

I suspect that this happens, because the key in SafeEvpPKeyHandle isn't private. But when i cal this:

pkcs11-tool --module /usr/lib/libtpm2_pkcs11.so --list-objects -l --pin 1234567890

I can see that there is private and public object:

ERROR:fapi:src/tss2-fapi/api/Fapi_List.c:221:Fapi_List_Finish() FAPI not provisioned.
ERROR:fapi:src/tss2-fapi/api/Fapi_List.c:81:Fapi_List() ErrorCode (0x00060034) Entities_List
ERROR: Listing FAPI token objects failed.
Using slot 0 with a present token (0x1)
Public Key Object; RSA 1024 bits
  label:      tls
  ID:         cd924ad983bc51ca1f15f446630901fa835f7b45
  Usage:      encrypt, verify, wrap
  Access:     local
Private Key Object; RSA
  label:      tls
  ID:         cd924ad983bc51ca1f15f446630901fa835f7b45
  Usage:      decrypt, sign, unwrap
  Access:     sensitive, always sensitive, never extractable, local
  Allowed mechanisms: RSA-X-509,RSA-PKCS-OAEP,RSA-PKCS,SHA1-RSA-PKCS,SHA256-RSA-PKCS,SHA384-RSA-PKCS,SHA512-RSA-PKCS,RSA-PKCS-PSS,SHA1-RSA-PKCS-PSS,SHA256-RSA-PKCS-PSS,SHA384-RSA-PKCS-PSS,SHA512-RSA-PKCS-PSS

Maybe i'm giving some wrong parameters for retrievieng the private key from the engine?

BR
Piotr
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