CODEWITHSUNDEEP
windows-mobilecertificatex509
Gene
Gene

Reputation: 4242

Calculate key identifier of a X509 certificate

I'd like to calculate the CERT_KEY_IDENTIFIER_PROP_ID of a X509 certificate to add it silently to the registry of a Windows Mobile device (during staging). As of this site, it's calculated like this:

SEQ[SEQ[rsa], key]

I guess the key is cert.GetPublicKey(), but what's meant with rsa here (not the algorithm I guess)?

Searching the web for three hours now, I would be very glad if someone could point me into the right direction.

Upvotes: 1

Views: 542

Answers (1)

Gene
Gene

Reputation: 4242

To read the properties I need to write to the registry key, I finally used the following CryptoAPI methods:

[DllImport("crypt32.dll", SetLastError = true)]
private static extern IntPtr CertCreateCertificateContext(int dwCertEncodingType, byte[] pbCertEncoded, int cbCertEncoded);

[DllImport("crypt32.dll", SetLastError = true)]
private static extern bool CertFreeCertificateContext(IntPtr pCertContext);

[DllImport("crypt32.dll", SetLastError = true)]
private static extern bool CertGetCertificateContextProperty(IntPtr pCertContext, int dwPropId, IntPtr pvData, ref int pcbData);

private byte[] GetKeyIdentifier(X509Certificate certificate)
{
  var data = certificate.GetRawCertData();

  var context = CertCreateCertificateContext(1, data, data.Length);

  try
  {
    return ReadProperty(context, 0x14);
  }
  finally
  {
    CertFreeCertificateContext(context);
  }
}

private byte[] ReadProperty(IntPtr context, int property)
{
  var length = 0;

  // determine the ammount of memory to allocate for the data
  if (CertGetCertificateContextProperty(context, property, IntPtr.Zero, ref length))
  {
    var pointer = Marshal.AllocCoTaskMem(length);

    try
    {
      // query the property which is written to the allocated memory
      if (CertGetCertificateContextProperty(context, property, pointer, ref length) == false)
      {
        throw new InvalidOperationException(string.Format("Failed to query property {0}.", property));
      }

      // extract the data from the unmanaged memory
      var buffer = new byte[length];
      Marshal.Copy(pointer, buffer, 0, length);

      return buffer;
    }
    finally
    {
      Marshal.FreeCoTaskMem(pointer);
    }
  }
  else
  {
    throw new InvalidOperationException(string.Format("Failed to query property {0}.", property));
  }
}

Upvotes: 3

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