关于 .net Framework 4.7 中 ECDiffieHellmanCng 实施的秘密协议的问题？

Question

我有以下代码：

        var curve = ECCurve.NamedCurves.nistP256;
        var ecdhSender = ECDiffieHellman.Create(curve);
        var ecdhReceiver = ECDiffieHellman.Create(curve);

我的理解是，我应该能够通过使用 ecdhReceiver.PublicKey 使用 ecdhSender 对象或使用 ecdhSender.PublicKey 使用 ecdhReceiver 对象来计算秘密协议，并且两个秘密协议值应该相同。如果这是一个错误的假设，请告诉我。

由于ECDiffieHellman.Create returns ECDiffieHellman类型，我写了下面的代码来获取秘密协议：

        string receiverHexString = null;
        using (SafeNCryptSecretHandle secretAgreement = (ecdhReceiver as ECDiffieHellmanCng).DeriveSecretAgreementHandle(ecdhSender.PublicKey))
        {
            byte[] secretAgreementBytes = new byte[32];
            IntPtr pointer = secretAgreement.DangerousGetHandle();
            Marshal.Copy(pointer, secretAgreementBytes, 0, secretAgreementBytes.Length);
            receiverHexString = BitConverter.ToString(secretAgreementBytes).Replace("-", string.Empty).ToLower();
            Console.WriteLine($"receiver secretAgreement: 0x{receiverHexString}");
        }

        string senderHexString = null;
        using (SafeNCryptSecretHandle secretAgreement = (ecdhSender as ECDiffieHellmanCng).DeriveSecretAgreementHandle(ecdhReceiver.PublicKey))
        {
            byte[] secretAgreementBytes = new byte[32];
            IntPtr pointer = secretAgreement.DangerousGetHandle();
            Marshal.Copy(pointer, secretAgreementBytes, 0, secretAgreementBytes.Length);
            senderHexString = BitConverter.ToString(secretAgreementBytes).Replace("-", string.Empty).ToLower();
            Console.WriteLine($"sender secretAgreement: 0x{senderHexString}");
        }

        Assert.AreEqual(receiverHexString, senderHexString);

我的断言失败了。显然我做错了什么（如果秘密协议应该相同的话）。

这是我从句柄中提取字节的方式吗？或者别的什么？

Answer 1

从开始，没有记录的方法从 CNG 获取原始秘密协议值，这就是 .NET 不公开它的原因。

.NET 中 ECDH 的预期用途是

ECCurve curve = ECCurve.NamedCurves.nistP256;

// Usually you'll only have one private key (yours), so this isn't representative of
// real code.  An `ECDiffieHellman` object doesn't necessarily have a private key,
// but an `ECDiffieHellmanPublicKey` object definitely doesn't.
using (ECDiffieHellman bobPrivate = ECDiffieHellman.Create(curve))
using (ECDiffieHellman alicePrivate = ECDiffieHellman.Create(curve))
using (ECDiffieHellmanPublicKey bobPublic = bobPrivate.PublicKey)
using (ECDiffieHellmanPublicKey alicePublic = alicePrivate.PublicKey)
{
    byte[] ba = bobPrivate.DeriveKeyFromHash(alicePublic, HashAlgorithmName.SHA256);
    byte[] ab = alicePrivate.DeriveKeyFromHash(bobPublic, HashAlgorithmName.SHA256);

    // ba and ab have the same contents.
}

还有

DeriveKeyFromHash(ECDiffieHellmanPublicKey otherPartyPublicKey, HashAlgorithmName hashAlgorithm, byte[] secretPrepend, byte[] secretAppend)
DeriveKeyFromHmac(ECDiffieHellmanPublicKey otherPartyPublicKey, HashAlgorithmName hashAlgorithm, byte[] hmacKey)
DeriveKeyFromHmac(ECDiffieHellmanPublicKey otherPartyPublicKey, HashAlgorithmName hashAlgorithm, byte[] hmacKey, byte[] secretPrepend, byte[] secretAppend)
DeriveKeyTls(ECDiffieHellmanPublicKey otherPartyPublicKey, byte[] prfLabel, byte[] prfSeed)

如果 bobPrivate 和 alicePublic（或者相反，alicePrivate 和 bobPublic）不变，那么提供相同的输入将产生相同的输出。

注意： 如果可以，您应该避免具体谈论 ECDiffieHellmanCng。当 ECDH 最终进入 .NET 标准时，ECDHCng class 不会。从 .NET 4.6.2 开始，一切都可以在基础 class 上完成（打开持久密钥除外）； .NET Core 倾向于不 return public 类型来自其 Create() 工厂方法。

关于 .net Framework 4.7 中 ECDiffieHellmanCng 实施的秘密协议的问题？

Questions about secret agreement from ECDiffieHellmanCng implementation in .net framework 4.7?

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cryptography

elliptic-curve