C＃如何验证Root-CA-Cert证书（x509）链？

Posted 2021-04-19

假设我有三个证书（Base64格式）

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都不在我的计算机证书库中）

编辑：BouncyCastle具有验证功能。但我试图不使用任何第三方库。

    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未由cert2（CA或root）签名，则会出现异常。这正是我想要的。

答案

X509Chain类旨在实现这一目标，您甚至可以自定义它如何执行链构建过程。

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);
}

如果需要，X509Chain将包含有关Build() == false之后验证失败的其他信息。

编辑：这只会确保您的CA有效。如果要确保链条相同，可以手动检查指纹。您可以使用以下方法来确保认证链是正确的，它期望链中的顺序：..., 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;
}

我无法测试这个，因为我没有完整的CA链，所以最好调试并逐步完成代码。