是否ECDiffieHellmanCng在.NET中有一个实现NIST SP 800-56A，第5.8.1节一密钥导出函数

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问题描述

我手头需要导出使用NIST SP 800-56A，第5.8.1节中描述的密钥导出功能键材料的任务。我不是在密码学方面的专家，所以如果这个问题是幼稚的，请原谅我。以下是我迄今所做的：

I have a task at hand that requires deriving key material using the key derivation function described in NIST SP 800-56A, section 5.8.1. I'm not an expert in Cryptography so please excuse me if the question is naive. Here's what I've done so far:

我有对方的公钥和我的私钥

现在，我尝试生成像这样的使用ECDH 1.3.132.1.12使用C＃共享密钥（.NET 4）ECDiffieHellmanCng类：

I have the other party's public key and my private key
Now I try to generate the shared secret using ECDH 1.3.132.1.12 using C# (.NET 4) ECDiffieHellmanCng class like so:

// The GetCngKey method reads the private key from a certificate in my Personal certificate store

CngKey cngPrivateKey = GetCngKey();

ECDiffieHellmanCng ecDiffieHellmanCng = new ECDiffieHellmanCng(cngPrivateKey);

ecDiffieHellmanCng.HashAlgorithm = CngAlgorithm.ECDiffieHellmanP256;
ecDiffieHellmanCng.KeyDerivationFunction = ?? // What do I set here

最后做到这一点：

ecDiffieHellmanCng.DeriveKeyMaterial(otherPartyPublicKey:);

在哪里/我该如何设置其他参数算法ID，U方信息，甲方V的信息？

Where/how do I set the other parameters Algorithm ID, Party U Info, Party V Info?

修改
我打开使用其他库，例如充气城堡（前提是他们可以从.NET调用）

EDITI am open to using other libraries like Bouncy Castle (provided they can be called from .NET)

推荐答案

TL; DR;我还没有找到一种方式来获得使用KDF在NIST SP 800-56A描述的对称密钥，第5.8.1节使用在.NET 4.0中单独内置类

TL;DR; I haven't found a way to derive the symmetric key using KDF described in NIST SP 800-56A, section 5.8.1 using built-in classes in .NET 4.0 alone

好消息（对我:-)）是它采用了可爱BouncyCastle的库在.NET 4.0中是可能的（的NuGet：安装封装BouncyCastle的-外部-Version1.7.0）。具体方法如下：

The good news (for me :-)) is that it IS possible in .NET 4.0 using the lovely BouncyCastle library (NuGet: Install-Package BouncyCastle-Ext -Version "1.7.0"). Here's how:

第1步：获取对方的公钥

STEP 1: Get other party's public key

根据你的情况下，这可以由一个证书读取或来给你为包含加密的数据的消息的一部分。一旦你的Base64编码的连接codeD公共密钥，它读入一个Org.BouncyCastle.Crypto.Parameters.ECPublicKeyParameters对象，像这样：

Depending on your scenario, this may be read from a certificate or come to you as part of the message containing the encrypted data. Once you have the Base64 encoded public-key, read it into a Org.BouncyCastle.Crypto.Parameters.ECPublicKeyParameters object like so:

var publicKeyBytes = Convert.FromBase64String(base64PubKeyStr);
ECPublicKeyParameters otherPartyPublicKey = (ECPublicKeyParameters)PublicKeyFactory.CreateKey(publicKeyBytes);

第2步：读您的私人密钥

STEP 2: Read your private-key

这将最通常涉及读取从PFX / P12证书的私钥。 Windows帐户运行code应该有机会获得PFX / P12，另外，如果证书导入证书存储区，你需要通过所有任务授予的权限 - >在certmgr管理私钥菜单。 MSC

This would most-commonly involve reading the private key from a PFX/P12 certificate. The windows account running the code should have access to the PFX/P12 and additionally, if the certificate is imported into a certificate store, you'll need to grant permissions via the All Tasks -> manage private key menu in certmgr.msc

using (StreamReader reader = new StreamReader(path))
{
    var fs = reader.BaseStream;
    string password = "<password for the PFX>";
    Pkcs12Store store = new Pkcs12Store(fs, passWord.ToCharArray());

   foreach (string n in store.Aliases)
   {
       if (store.IsKeyEntry(n))
       {
           AsymmetricKeyEntry asymmetricKey = store.GetKey(n);

           if (asymmetricKey.Key.IsPrivate)
           {
               ECPrivateKeyParameters privateKey = asymmetricKey.Key as ECPrivateKeyParameters;
           }
       }
   }
}

第3步：计算共享的秘密

STEP 3: Compute the shared secret

IBasicAgreement aKeyAgree = AgreementUtilities.GetBasicAgreement("ECDH");
aKeyAgree.Init(privateKey);
BigInteger sharedSecret = aKeyAgree.CalculateAgreement(otherPartyPublicKey);
byte[] sharedSecretBytes = sharedSecret.ToByteArray();

步骤4：prepare信息来计算对称密钥要求：

STEP 4: Prepare information required to compute symmetric key:

byte[] algorithmId = Encoding.ASCII.GetBytes(("<prependString/Hex>" + "id-aes256-GCM"));
byte[] partyUInfo = Encoding.ASCII.GetBytes("<as-per-agreement>");
byte[] partyVInfo = <as-per-agreement>;
MemoryStream stream = new MemoryStream(algorithmId.Length + partyUInfo.Length + partyVInfo.Length);
var sr = new BinaryWriter(stream);
sr.Write(algorithmId);
sr.Flush();
sr.Write(partyUInfo);
sr.Flush();
sr.Write(partyVInfo);
sr.Flush();
stream.Position = 0;
byte[] keyCalculationInfo = stream.GetBuffer();

步骤5：导出对称密钥

// NOTE: Use the digest/Hash function as per your agreement with the other party
IDigest digest = new Sha256Digest();
byte[] symmetricKey = new byte[digest.GetDigestSize()];
digest.Update((byte)(1 >> 24));
digest.Update((byte)(1 >> 16));
digest.Update((byte)(1 >> 8));
digest.Update((byte)1);
digest.BlockUpdate(sharedSecret, 0, sharedSecret.Length);
digest.BlockUpdate(keyCalculationInfo, 0, keyCalculationInfo.Length);
digest.DoFinal(symmetricKey, 0);

现在你有对称密钥准备做解密。以使用AES执行解密，BouncyCastle的IWrapper可以使用。通过调用WrapperUtilities.GetWrapper（AES //）获得使用Org.BouncyCastle.Security.WrapperUtilities的IWrapper例如AES / CBC / PKCS7。这也将取决于通信双方之间的协议。

Now you have the symmetric key ready to do the decryption. To perform decryption using AES, BouncyCastle IWrapper can be used. Obtain an IWrapper using Org.BouncyCastle.Security.WrapperUtilities by calling WrapperUtilities.GetWrapper("AES//") e.g. "AES/CBC/PKCS7". This will also depend on the agreement between the two communicating parties.

初始化密码（IWrapper）对称密钥和初始化向量（IV），并调用展开方法来获取纯文本字节。最后，转换为字符串使用使用的字符编码（如UTF8 / ASCII / UNI code）

Initialize the cipher (IWrapper) with symmetric key and initialization vector (IV) and call the Unwrap method to get plain-text bytes. Finally, convert to string literal using the character encoding used (e.g. UTF8/ASCII/Unicode)

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