C# 如何验证 Root-CA-Cert 证书 (x509) 链?

问题描述

假设我有三个证书(Base64 格式)

Let's say I have three certificates (in Base64 format)

Root
 |
 --- CA
     |
     --- Cert (client/signing/whatever)

如何在 C# 中验证证书和证书路径/链?(所有这三个证书可能不在我的计算机证书存储中)

How can I validate the certs and certificate path/chain in C#? (All those three certs may not be in my computer cert store)

编辑:BouncyCastle 具有验证功能.但我尽量不使用任何第三方库.

Edit: BouncyCastle has the function to verify. But I'm trying not to use any third-party library.

    byte[] b1 = Convert.FromBase64String(x509Str1);
    byte[] b2 = Convert.FromBase64String(x509Str2);
    X509Certificate cer1 = 
        new X509CertificateParser().ReadCertificate(b1);
    X509Certificate cer2 =
        new X509CertificateParser().ReadCertificate(b2);
    cer1.Verify(cer2.GetPublicKey());

如果 cer1 没有被 cert2(CA 或 root)签名，就会出现异常.这正是我想要的.

If the cer1 is not signed by cert2 (CA or root), there will be exception. This is exactly what I want.

推荐答案

X509Chain 类就是为此而设计的，您甚至可以自定义它如何执行链构建过程.

The X509Chain class was designed to do this, you can even customize how it performs the chain building process.

static bool VerifyCertificate(byte[] primaryCertificate, IEnumerable<byte[]> additionalCertificates)
{
    var chain = new X509Chain();
    foreach (var cert in additionalCertificates.Select(x => new X509Certificate2(x)))
    {
        chain.ChainPolicy.ExtraStore.Add(cert);
    }

    // You can alter how the chain is built/validated.
    chain.ChainPolicy.RevocationMode = X509RevocationMode.NoCheck;
    chain.ChainPolicy.VerificationFlags = X509VerificationFlags.IgnoreWrongUsage;

    // Do the validation.
    var primaryCert = new X509Certificate2(primaryCertificate);
    return chain.Build(primaryCert);
}

如果您需要，X509Chain 将包含有关 Build() == false 之后验证失败的附加信息.

The X509Chain will contain additional information about the validation failure after Build() == false if you need it.

这只会确保您的 CA 有效.如果要确保链相同，可以手动检查指纹.可以使用下面的方法来保证认证链是正确的，它期望链的顺序是:..., INTERMEDIATE2, INTERMEDIATE1 (Signer of INTERMEDIATE2), CA (Signer of INTERMEDIATE1)

This will merely ensure that your CA's are valid. If you want to ensure that the chain is identical you can check the thumbprints manually. You can use the following method to ensure that the certification chain is correct, it expects the chain in the order: ..., INTERMEDIATE2, INTERMEDIATE1 (Signer of INTERMEDIATE2), CA (Signer of INTERMEDIATE1)

static bool VerifyCertificate(byte[] primaryCertificate, IEnumerable<byte[]> additionalCertificates)
{
    var chain = new X509Chain();
    foreach (var cert in additionalCertificates.Select(x => new X509Certificate2(x)))
    {
        chain.ChainPolicy.ExtraStore.Add(cert);
    }

    // You can alter how the chain is built/validated.
    chain.ChainPolicy.RevocationMode = X509RevocationMode.NoCheck;
    chain.ChainPolicy.VerificationFlags = X509VerificationFlags.IgnoreWrongUsage;

    // Do the preliminary validation.
    var primaryCert = new X509Certificate2(primaryCertificate);
    if (!chain.Build(primaryCert))
        return false;

    // Make sure we have the same number of elements.
    if (chain.ChainElements.Count != chain.ChainPolicy.ExtraStore.Count + 1)
        return false;

    // Make sure all the thumbprints of the CAs match up.
    // The first one should be 'primaryCert', leading up to the root CA.
    for (var i = 1; i < chain.ChainElements.Count; i++)
    {
        if (chain.ChainElements[i].Certificate.Thumbprint != chain.ChainPolicy.ExtraStore[i - 1].Thumbprint)
            return false;
    }

    return true;
}

我无法对此进行测试，因为我没有完整的 CA 链，因此最好调试并逐步执行代码.

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