使用 oldschool .NET 导出 CNG RSA 证书的私钥 (PKCS#8)

Question

我有一个 PKCS #12 (PFX) 文件，它是一个带有 CNG RSA 密钥的证书，我想导出私钥。

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MfAVl0oh+KBfFBh+2O+zNA+qRBBTacVg8LCnjGHYUuC+PXDW7UOVSNgICB9A=

文件为复制样本，密码为：1234

我已经尝试导出 RsaParameters 以及从 CngKey 导出私钥但没有成功 - operation not supported.

问题是缺少 CngExportPolicies.AllowPlaintextExport 标志。由于密钥处于最终状态，因此我也没有成功使用本机 NCrypt 调用设置标志。

在另一个问题评论 () 中有关于流程（导出、导入和设置标志和导出）的提示，它也指向几行 .NET 核心代码。

我试图将代码移植到旧式 C# .NET（例如没有 Span<T>），但在以下调用中得到 invalid argument：

    internal static unsafe bool ExportPkcs8KeyBlob(
        SafeNCryptKeyHandle keyHandle,
        string password,
        int kdfCount,
        out int bytesWritten,
        out byte[] allocated)
    {
      using (var stringHandle = new SafeUnicodeStringHandle(password))
      {
        var pbrParamsPtr =
          Marshal.AllocHGlobal(Marshal.SizeOf(typeof(NativeMethods.NCrypt.PbeParams)));
        var pbeParams = new NativeMethods.NCrypt.PbeParams();
        fixed (byte* oidPtr = s_pkcs12TripleDesOidBytes)
        {

          var salt = new byte[8];
          RandomNumberGenerator.GetBytes(salt);
          pbeParams.rgbSalt = salt;
          pbeParams.Params.cbSalt = pbeParams.rgbSalt.Length;
          pbeParams.Params.iIterations = kdfCount;

          var buffers = stackalloc NativeMethods.NCrypt.NCryptBuffer[3];
          buffers[0] = new NativeMethods.NCrypt.NCryptBuffer
          {
            BufferType = NativeMethods.NCrypt.BufferType.PkcsSecret,
            cbBuffer = checked(2 * (password.Length + 1)),
            pvBuffer = stringHandle.DangerousGetHandle(),
          };

          if (buffers[0].pvBuffer == IntPtr.Zero)
          {
            buffers[0].cbBuffer = 0;
          }

          buffers[1] = new NativeMethods.NCrypt.NCryptBuffer
          {
            BufferType = NativeMethods.NCrypt.BufferType.PkcsAlgOid,
            cbBuffer = s_pkcs12TripleDesOidBytes.Length,
            pvBuffer = (IntPtr)oidPtr,
          };

          Marshal.StructureToPtr(pbeParams, pbrParamsPtr, true);
          buffers[2] = new NativeMethods.NCrypt.NCryptBuffer
          {
            BufferType = NativeMethods.NCrypt.BufferType.PkcsAlgParam,
            cbBuffer = Marshal.SizeOf(typeof(NativeMethods.NCrypt.PbeParams)),
            pvBuffer = pbrParamsPtr
          };

          var desc = new NativeMethods.NCrypt.NCryptBufferDesc
          {
            cBuffers = 3,
            pBuffers = (IntPtr)buffers,
            ulVersion = 0,
          };


          var pbOutput = Array.Empty<byte>();
          var errorCode = NativeMethods.NCrypt.NCryptExportKey(
              keyHandle,
              IntPtr.Zero,
              NCRYPT_PKCS8_PRIVATE_KEY_BLOB,
              ref desc,
              ref pbOutput,
              0,
              out int numBytesNeeded,
              0);

          if (errorCode != 0)
          {
            throw new Win32Exception(errorCode);
...

我为完整代码创建了一个存储库，其中的单元测试在 github 处失败：https://github.com/lennybacon/CngPfxKeyExport

欢迎任何我从 .Net Core 转换失败或填充错误数据或指针的提示，因为关于用法的文档似乎非常罕见...

Answer 1

您似乎引入了两个主要的移植错误和一个调用本机方法的错误：

1) PbeParams.

你的：

[StructLayout(LayoutKind.Sequential)]
internal struct PbeParams
{
    internal const int RgbSaltSize = 8;

    internal CryptPkcs12PbeParams Params;
    internal byte[] rgbSalt;
}

核心外汇：

[StructLayout(LayoutKind.Sequential)]
internal unsafe struct PBE_PARAMS
{
    internal const int RgbSaltSize = 8;

    internal CRYPT_PKCS12_PBE_PARAMS Params;
    internal fixed byte rgbSalt[RgbSaltSize];
}

你记忆中的布局是在CRYPT_PKCS12_PBE_PARAMS值之后是一个指向更多数据的指针。 CoreFX 版本的布局是紧接在 CRYPT_PKCS12_PBE_PARAMS 之后的是 8 个字节的盐占位符，这是加密 API 所期望的（因为它不采用 pbSalt）。

恢复 fixed byte rgbSalt[RgbSaltSize] 很重要。

2) NCryptExportKey 的 pbOutput:

你的：

[DllImport("ncrypt.dll", CharSet = CharSet.Unicode)]
internal static extern int NCryptExportKey(
    SafeNCryptKeyHandle hKey,
    IntPtr hExportKey,
    string pszBlobType,
    ref NCryptBufferDesc pParameterList,
    ref byte[] pbOutput,
    int cbOutput,
    [Out] out int pcbResult,
    int dwFlags);

核心外汇：

[DllImport(Interop.Libraries.NCrypt, CharSet = CharSet.Unicode)]
internal static extern ErrorCode NCryptExportKey(
    SafeNCryptKeyHandle hKey,
    IntPtr hExportKey,
    string pszBlobType,
    ref NCryptBufferDesc pParameterList,
    ref byte pbOutput,
    int cbOutput,
    [Out] out int pcbResult,
    int dwFlags);

值得注意的是，CoreFX 版本是 ref byte pbOutput 而你的版本是 ref byte[] pbOutput，使得值因指针间接而不同。

3) 第一次调用导出需要 C NULL，不是有效指针。

将更正后的互操作代码压缩到一个文件中，删除注释和未使用的枚举成员（以减少 post 大小）并修复它（然后简化使用，因为您可以使用 string（保证 [=23=] 终止符）而不是 ReadOnlySpan<char>（无终止符保证））在 .NET Framework 4.7.2 上产生这个：

internal static class CngEncryptedExport
{
    internal const string NCRYPT_PKCS8_PRIVATE_KEY_BLOB = "PKCS8_PRIVATEKEY";
    private static readonly byte[] s_pkcs12TripleDesOidBytes =
        System.Text.Encoding.ASCII.GetBytes("1.2.840.113549.1.12.1.3[=14=]");

    internal static void Go()
    {
        using (var cert = new X509Certificate2(s_pfx, PfxPassword, X509KeyStorageFlags.Exportable))
        using (RSA rsa = cert.GetRSAPrivateKey())
        {
            RSACng rsaCng = (RSACng)rsa;

            using (CngKey key = rsaCng.Key)
            {
                Console.WriteLine(key.ExportPolicy);

                Console.WriteLine(
                    Convert.ToBase64String(
                        ExportPkcs8KeyBlob(key.Handle, "123", 21)));
            }
        }
    }

    private static unsafe byte[] ExportPkcs8KeyBlob(
        SafeNCryptKeyHandle keyHandle,
        string password,
        int kdfCount)
    {
        var pbeParams = new NativeMethods.NCrypt.PbeParams();
        NativeMethods.NCrypt.PbeParams* pbeParamsPtr = &pbeParams;

        byte[] salt = new byte[NativeMethods.NCrypt.PbeParams.RgbSaltSize];

        using (RandomNumberGenerator rng = RandomNumberGenerator.Create())
        {
            rng.GetBytes(salt);
        }

        pbeParams.Params.cbSalt = salt.Length;
        Marshal.Copy(salt, 0, (IntPtr)pbeParams.rgbSalt, salt.Length);
        pbeParams.Params.iIterations = kdfCount;

        fixed (char* stringPtr = password)
        fixed (byte* oidPtr = s_pkcs12TripleDesOidBytes)
        {
            NativeMethods.NCrypt.NCryptBuffer* buffers =
                stackalloc NativeMethods.NCrypt.NCryptBuffer[3];

            buffers[0] = new NativeMethods.NCrypt.NCryptBuffer
            {
                BufferType = NativeMethods.NCrypt.BufferType.PkcsSecret,
                cbBuffer = checked(2 * (password.Length + 1)),
                pvBuffer = (IntPtr)stringPtr,
            };

            if (buffers[0].pvBuffer == IntPtr.Zero)
            {
                buffers[0].cbBuffer = 0;
            }

            buffers[1] = new NativeMethods.NCrypt.NCryptBuffer
            {
                BufferType = NativeMethods.NCrypt.BufferType.PkcsAlgOid,
                cbBuffer = s_pkcs12TripleDesOidBytes.Length,
                pvBuffer = (IntPtr)oidPtr,
            };

            buffers[2] = new NativeMethods.NCrypt.NCryptBuffer
            {
                BufferType = NativeMethods.NCrypt.BufferType.PkcsAlgParam,
                cbBuffer = sizeof(NativeMethods.NCrypt.PbeParams),
                pvBuffer = (IntPtr)pbeParamsPtr,
            };

            var desc = new NativeMethods.NCrypt.NCryptBufferDesc
            {
                cBuffers = 3,
                pBuffers = (IntPtr)buffers,
                ulVersion = 0,
            };

            int result = NativeMethods.NCrypt.NCryptExportKey(
                keyHandle,
                IntPtr.Zero,
                NCRYPT_PKCS8_PRIVATE_KEY_BLOB,
                ref desc,
                null,
                0,
                out int bytesNeeded,
                0);

            if (result != 0)
            {
                throw new Win32Exception(result);
            }

            byte[] exported = new byte[bytesNeeded];

            result = NativeMethods.NCrypt.NCryptExportKey(
                keyHandle,
                IntPtr.Zero,
                NCRYPT_PKCS8_PRIVATE_KEY_BLOB,
                ref desc,
                exported,
                exported.Length,
                out bytesNeeded,
                0);

            if (result != 0)
            {
                throw new Win32Exception(result);
            }

            if (bytesNeeded != exported.Length)
            {
                Array.Resize(ref exported, bytesNeeded);
            }

            return exported;
        }
    }

    private static class NativeMethods
    {
        internal static class NCrypt
        {
            [DllImport("ncrypt.dll", CharSet = CharSet.Unicode)]
            internal static extern int NCryptExportKey(
                SafeNCryptKeyHandle hKey,
                IntPtr hExportKey,
                string pszBlobType,
                ref NCryptBufferDesc pParameterList,
                byte[] pbOutput,
                int cbOutput,
                [Out] out int pcbResult,
                int dwFlags);

            [StructLayout(LayoutKind.Sequential)]
            internal unsafe struct PbeParams
            {
                internal const int RgbSaltSize = 8;

                internal CryptPkcs12PbeParams Params;
                internal fixed byte rgbSalt[RgbSaltSize];
            }

            [StructLayout(LayoutKind.Sequential)]
            internal struct CryptPkcs12PbeParams
            {
                internal int iIterations;
                internal int cbSalt;
            }

            [StructLayout(LayoutKind.Sequential)]
            internal struct NCryptBufferDesc
            {
                public int ulVersion;
                public int cBuffers;
                public IntPtr pBuffers;
            }

            [StructLayout(LayoutKind.Sequential)]
            internal struct NCryptBuffer
            {
                public int cbBuffer;
                public BufferType BufferType;
                public IntPtr pvBuffer;
            }

            internal enum BufferType
            {
                PkcsAlgOid = 41,
                PkcsAlgParam = 42,
                PkcsSecret = 46,
            }
        }
    }

    // PFX and password omitted
}

使用 oldschool .NET 导出 CNG RSA 证书的私钥 (PKCS#8)

Export private key (PKCS#8) of CNG RSA certificate with oldschool .NET

.net

pinvoke

rsa

certificate

cng