The CryptVerifyDetachedMessageSignature function verifies a signed message's signature.

C# Signature:

    [DllImport("Crypt32.dll", SetLastError = true)]
    static internal extern bool CryptVerifyDetachedMessageSignature(
        ref CRYPT_VERIFY_MESSAGE_PARA pVerifyPara,
        int dwSignerIndex,
        byte[] pbDetachedSignBlob,
        int cbDetachedSignBlob,
        int cToBeSigned,
        IntPtr[] rgpbToBeSigned,
        int[] rgcbToBeSigned,
        IntPtr ppSignerCert);

VB Signature:

Declare Function CryptVerifyDetachedMessageSignature Lib "crypt32.dll" (TODO) As TODO

User-Defined Types:

None.

Notes:

None.

Tips & Tricks:

Please add some!

Sample Code:

  public void VerifyDetachedMessageSignature2(byte[] messageData, byte[] signatureData, out byte[] p_x509)
  {
    CRYPT_VERIFY_MESSAGE_PARA verifyParams;
    IntPtr buffer = Marshal.AllocCoTaskMem(Marshal.SizeOf(typeof(byte)) * messageData.Length);
    Marshal.Copy(messageData, 0, buffer, messageData.Length);
    IntPtr[] rgpbToBeSigned = new IntPtr[1] { buffer };
    int[] rgcbToBeSigned = new int[1] { messageData.Length };

    p_x509 = null;
    GCHandle pCertContext;

    verifyParams = new CRYPT_VERIFY_MESSAGE_PARA();
    verifyParams.cbSize = (int)Marshal.SizeOf(verifyParams);
    verifyParams.dwMsgAndCertEncodingType = CryptoConstants.X509_ASN_ENCODING | CryptoConstants.PKCS_7_ASN_ENCODING;
    verifyParams.hCryptProv = 0;
    verifyParams.pfnGetSignerCertificate = IntPtr.Zero;
    verifyParams.pvGetArg = IntPtr.Zero;

    pCertContext = GCHandle.Alloc(IntPtr.Zero, GCHandleType.Pinned);

    try
    {
        bool res = CryptoApiProvider.CryptVerifyDetachedMessageSignature(
        ref verifyParams,     // Verify parameters.
        0,            // Signer index.
        signatureData,        // Buffer for decoded message.
        signatureData.Length,     // Size of buffer.
1,         rgpbToBeSigned,       // Pointer to signed BLOB.
        rgcbToBeSigned,       // Size of signed BLOB.
        pCertContext.AddrOfPinnedObject());

        if (!res)
        {
        throw new Exception("Error while encrypting data [" + Marshal.GetLastWin32Error() + "].");
        }

        try
        {
        X509Certificate x509 = new X509Certificate( ( IntPtr )pCertContext.Target );
        }
        finally
        {
        Crypt32.CertFreeCertificateContext( ( IntPtr )pCertContext.Target );
        }
    }
    finally
    {
        pCertContext.Free();
    }
  }

Alternative Managed API:

Do you know one? Please contribute it!