在C#中使用ECDSA生成证书

Question

openssl ecparam -genkey -name secp256r1 -out mykey.key
openssl req -new -key mykey.key -out myreq.csr
openssl req -x509 -days 7 -key mykey.key -in myreq.csr -out mycert.crt
openssl pkcs12 -export -out mycert.pfx -inkey mykey.key -in mycert.crt

我已经使用BouncyCastle来帮助创建基于RSA的证书，因此接下来的步骤或多或少遵循了创建RSA证书的方法。

（注意，bc前缀用于来自BouncyCastle的类，ms用于.NET类）

1生成密钥对：私钥和公钥

BC.IAsymmetricCipherKeyPairGenerator bcKpGen = BC.GeneratorUtilities.GetKeyPairGenerator("ECDSA");
bcKpGen.Init(new BC.ECKeyGenerationParameters(BC.SecObjectIdentifiers.SecP256r1, new BC.SecureRandom()));
BC.AsymmetricCipherKeyPair bcSubjKeys = bcKpGen.GenerateKeyPair();

BC.X509V3CertificateGenerator bcXgen = new BC.X509V3CertificateGenerator();
// .. set subject, validity period etc
bcXgen.SetPublicKey(bcSubjKeys.Public);
BC.ISignatureFactory bcSigFac = new BC.Asn1SignatureFactory("SHA256WITHECDSA", bcSubjKeys.Private);
BC.X509Certificate bcCert = bcXgen.Generate(bcSigFac);

如果我可以使用没有私钥的证书,则可以执行以下操作：

MS.X509Certificate mcCert = new MS.X509Certificate2(bcCert.GetEncoded(), null);

我就完蛋了。

当试图设置私钥时会出现问题：

msCert.PrivateKey = ConvertBouncyToNetSomehow(bcSubjKeys.Private)

BC.PrivateKeyInfo bcPKInfo = BC.PrivateKeyInfoFactory.CreatePrivateKeyInfo(bcSubjKeys.Private);
byte[] pkArr = bcPKInfo.GetDerEncoded();
MS.CngKey msPKCng = MS.CngKey.Import(pkArr, MS.CngKeyBlobFormat.Pkcs8PrivateBlob);

Answer 1

不幸的是，现在不可能直接跳出框框。您可以使用P/Invokes和.NET4.6.2（当前处于预览阶段）来完成其余的工作。或者，通过绕道.NET Core，您可以构建一个在.NET4.6.1中工作的PFX。

Windows CNG库将ECC拆分为ECDSA和ECDH。ECDSA密钥对象只能用于ECDSA；但每当Windows无法确定PFX导入（或PKCS#8导入）期间的使用情况时，它就会调用私钥ECDH。为什么？由于Windows允许ECDH密钥对象同时进行密钥协商(ECDH)和数字签名(ECDSA)，因此ECDH更加灵活。

但.NET4.6.1并不知道这一点。

[DllImport(Libraries.Crypt32, CharSet = CharSet.Unicode, SetLastError = true)]
private static extern unsafe bool CertSetCertificateContextProperty(IntPtr pCertContext, CertContextPropId dwPropId, CertSetPropertyFlags dwFlags, SafeNCryptKeyHandle pvData);

internal enum CertContextPropId : int
{
    CERT_NCRYPT_KEY_HANDLE_PROP_ID = 78,
}

[Flags]
internal enum CertSetPropertyFlags : int
{
    None = 0,
}

private static X509Certificate2 MateECDsaPrivateKey(
    X509Certificate2 cert,
    CngKey privateKey)
{
    // Make a new certificate instance which isn't tied to the current one
    using (var tmpCert = new X509Certificate2(cert.RawData))
    {
        SafeNCryptKeyHandle keyHandle = privateKey.Handle;

        // Set the ephemeral key handle property
        if (!CertSetCertificateContextProperty(
            tmpCert.Handle,
            CertContextPropId.CERT_NCRYPT_KEY_HANDLE_PROP_ID,
            CertSetPropertyFlags.None,
            keyHandle))
        {
            throw new CryptographicException(Marshal.GetLastWin32Error());
        }

        // You could emit this, if you prefer.
        byte[] pfxBytes = tmpCert.Export(X509ContentType.Pkcs12);

        // Clear the key handle out again to prevent double-free
        keyHandle = new SafeNCryptKeyHandle();

        if (!CertSetCertificateContextProperty(
            tmpCert.Handle,
            CertContextPropId.CERT_NCRYPT_KEY_HANDLE_PROP_ID,
            CertSetPropertyFlags.None,
            keyHandle))
        {
            throw new CryptographicException(Marshal.GetLastWin32Error());
        }

        // Now load a new certificate which has a temporary keyfile on disk.
        // Note: If you don't want exportability here, don't request it.
        var matedCert = new X509Certificate2(pfxBytes, (string)null, X509KeyStorageFlags.Exportable);

        using (ECDsa ecdsa = matedCert.GetECDsaPrivateKey())
        {
            if (ecdsa == null)
            {
                throw new InvalidOperationException("It didn't work");
            }
        }

        return matedCert;
    }
}