c# - Silverlight でドキュメントにデジタル署名する

Question

Silverlight でファイルのデジタル署名を取得する際に問題があります。

crypt32.dll 関数を使用して署名付きハッシュを取得していますが、CryptSignMessage メソッドの結果として予期しないエラーが発生し、「パラメーターが正しくありません」と混乱します。

これが私のコードです：

  public byte[] SignData(IntPtr certContext, string signingText)
    {
        IntPtr buffer = IntPtr.Zero;
        Crypt32.CRYPT_SIGN_MESSAGE_PARA param = new Crypt32.CRYPT_SIGN_MESSAGE_PARA();
        Byte[] result = null;
        try
        {
            byte[] data = System.Text.Encoding.Unicode.GetBytes(signingText);
            IntPtr[] rgpbToBeSigned = new IntPtr[1];
            int[] rgcbToBeSigned = new int[1];
            IntPtr pSignerCert = certContext;
            buffer = Ole32.CoTaskMemAlloc((uint)(Marshal.SizeOf(data[0]) * data.Length));
            Marshal.Copy(data, 0, buffer, data.Length);
            rgpbToBeSigned[0] = buffer;
            rgcbToBeSigned[0] = 1;
            int resultlength = 0;

            param.dwMsgEncodingType = Crypt32.Constants.X509_ASN_ENCODING;
            param.pSigningCert = certContext;
            param.cbSize = Marshal.SizeOf(param);
            param.HashAlgorithm.pszObjId = "1.2.643.2.2.9";
            param.HashAlgorithm.Parameters.cbData = 0;
            param.HashAlgorithm.Parameters.pbData = null;
            param.pvHashAuxInfo = IntPtr.Zero;
            param.cMsgCert = 1;


            param.rgpMsgCert = kernel32.GlobalAlloc(0, (UIntPtr)(IntPtr.Size));
            Marshal.StructureToPtr(certContext, param.rgpMsgCert, false);
            if (Crypt32.CryptSignMessage(ref param, true, (int)1, rgpbToBeSigned, rgcbToBeSigned, result, ref resultlength) == false)
                throw new DB_Win32Exception(); //throws a string with error message from Getlastresult()

        }
        finally
        {
            if (!(param.rgpMsgCert == IntPtr.Zero))
             kernel32.LocalFree(param.rgpMsgCert);

            if (!(buffer == IntPtr.Zero))
             Ole32.CoTaskMemFree(buffer);
        }

これが私の外部メソッド宣言です：

        [DllImport("Crypt32.dll", SetLastError = true)]
        public static extern Boolean CryptSignMessage(
            ref CRYPT_SIGN_MESSAGE_PARA pSignPara,
            Boolean fDetachedSignature,
            Int32 cToBeSigned,
            IntPtr[] rgpbToBeSigned,
            Int32[] rgcbToBeSigned,
            Byte[] pbSignedBlob,
            ref Int32 pcbSignedBlob
        );

        [StructLayout(LayoutKind.Sequential)]
        public struct CRYPT_ALGORITHM_IDENTIFIER
        {
            [MarshalAs(UnmanagedType.LPStr, SizeConst = 100)] //???
            public String pszObjId;                             
            public CRYPTOAPI_BLOB Parameters;
        }
        [StructLayout(LayoutKind.Sequential)]
        public struct CRYPT_SIGN_MESSAGE_PARA
        {
            public Int32 cbSize;
            public Int32 dwMsgEncodingType;
            public IntPtr pSigningCert;
            public CRYPT_ALGORITHM_IDENTIFIER HashAlgorithm;
            public IntPtr pvHashAuxInfo;
            public Int32 cMsgCert;
            public IntPtr rgpMsgCert;
            public Int32 cMsgCrl;
            public IntPtr rgpMsgCrl;
            public Int32 cAuthAttr;
            public IntPtr rgAuthAttr;
            public Int32 cUnauthAttr;
            public IntPtr rgUnauthAttr;
            public Int32 dwFlags;
            public Int32 dwInnerContentType;
        }
        public struct CRYPTOAPI_BLOB
        {
            public Int32 cbData;
            [MarshalAs(UnmanagedType.ByValArray,SizeConst=999)] // ??? 
            public Byte[] pbData;
        }

問題がどこにあるかを特定する方法を知っている人はいますか?