cer证书签名验证[通俗易懂]

大家好，又见面了，我是你们的朋友全栈君。

一个cer证书本身也是需要签名的，这是为了防止cer证书被篡改。

证书有两种类型：

1. 根证书

2. 根证书签发的子证书。

根证书比较特殊，它是自签名的。而其他子证书的签名公钥都保存在它的上级证书里面。

可以用C#来做一些验证。

首先是根证书的签名验证。

        // 验证根证书签名
        X509Certificate2 x509Root = new X509Certificate2("C:\\Users\\kevin\\Desktop\\KevinRoot.cer");
        Console.WriteLine("Root Certificate Verified?: {0}{1}", x509Root.Verify(), Environment.NewLine);  // 根证书是自签名，所以可以通过。

很简单，因为根证书是自签名的，x509Root.Verify()会返回true。

然后是子证书的验证，

       X509Certificate2 x509 = new X509Certificate2("C:\\Users\\kevin\\Desktop\\ChildSubject2.cer");

        byte[] rawdata = x509.RawData;
        Console.WriteLine("Content Type: {0}{1}", X509Certificate2.GetCertContentType(rawdata), Environment.NewLine);
        Console.WriteLine("Friendly Name: {0}{1}", x509.FriendlyName, Environment.NewLine);
        Console.WriteLine("Certificate Verified?: {0}{1}", x509.Verify(), Environment.NewLine);
        Console.WriteLine("Simple Name: {0}{1}", x509.GetNameInfo(X509NameType.SimpleName, true), Environment.NewLine);
        Console.WriteLine("Signature Algorithm: {0}{1}", x509.SignatureAlgorithm.FriendlyName, Environment.NewLine);
    //    Console.WriteLine("Private Key: {0}{1}", x509.PrivateKey.ToXmlString(false), Environment.NewLine);  // cer里面并没有私钥信息
        Console.WriteLine("Public Key: {0}{1}", x509.PublicKey.Key.ToXmlString(false), Environment.NewLine);
        Console.WriteLine("Certificate Archived?: {0}{1}", x509.Archived, Environment.NewLine);
        Console.WriteLine("Length of Raw Data: {0}{1}", x509.RawData.Length, Environment.NewLine);

这里我用自己创建的子证书，x509.Verify()总是返回false，就算我把根证书导入到“trust”里面，还是返回false，不知道为什么。但是如果我用公司的证书（verisign颁发的），却可以返回true。不知道是不是我自己创建的根证书，子证书有什么配置问题，有空再研究。反正验证也就这么回事。

下面的代码，用来检查整个证书链。

        //Output chain information of the selected certificate.
        X509Chain ch = new X509Chain();
        ch.Build(x509);
        Console.WriteLine("Chain Information");
        ch.ChainPolicy.RevocationMode = X509RevocationMode.Online;
        Console.WriteLine("Chain revocation flag: {0}", ch.ChainPolicy.RevocationFlag);
        Console.WriteLine("Chain revocation mode: {0}", ch.ChainPolicy.RevocationMode);
        Console.WriteLine("Chain verification flag: {0}", ch.ChainPolicy.VerificationFlags);
        Console.WriteLine("Chain verification time: {0}", ch.ChainPolicy.VerificationTime);
        Console.WriteLine("Chain status length: {0}", ch.ChainStatus.Length);
        Console.WriteLine("Chain application policy count: {0}", ch.ChainPolicy.ApplicationPolicy.Count);
        Console.WriteLine("Chain certificate policy count: {0} {1}", ch.ChainPolicy.CertificatePolicy.Count, Environment.NewLine);
        //Output chain element information.
        Console.WriteLine("Chain Element Information");
        Console.WriteLine("Number of chain elements: {0}", ch.ChainElements.Count);
        Console.WriteLine("Chain elements synchronized? {0} {1}", ch.ChainElements.IsSynchronized, Environment.NewLine);

    //    int index = 0;
        foreach (X509ChainElement element in ch.ChainElements)
        {
            Console.WriteLine("Element subject name: {0}", element.Certificate.Subject);
            Console.WriteLine("Element issuer name: {0}", element.Certificate.Issuer);
            Console.WriteLine("Element certificate valid until: {0}", element.Certificate.NotAfter);
            Console.WriteLine("Element certificate is valid: {0}", element.Certificate.Verify());
            Console.WriteLine("Element error status length: {0}", element.ChainElementStatus.Length);
            Console.WriteLine("Element information: {0}", element.Information);
            Console.WriteLine("Number of element extensions: {0}{1}", element.Certificate.Extensions.Count, Environment.NewLine);

            string a = element.Certificate.Thumbprint;
       //     string b = ch.ChainPolicy.ExtraStore[0].Thumbprint;
            //ch.ChainPolicy.ExtraStore[index - 1].Thumbprint;

            if (ch.ChainStatus.Length > 1)
            {
                for (int index = 0; index < element.ChainElementStatus.Length; index++)
                {
                    Console.WriteLine(element.ChainElementStatus[index].Status);
                    Console.WriteLine(element.ChainElementStatus[index].StatusInformation);
                }
            }
        }

上面的代码也很简单，其实就是把整个证书链里面的每一个证书信息打印一下。具体的函数调用参数msdn。

下面是完整代码，注意里面的几个证书路径是我写死的，如果想测试下面的代码，只需要自己创建几个证书。

using System;
using System.Security.Cryptography;
using System.Security.Permissions;
using System.IO;
using System.Security.Cryptography.X509Certificates;

class CertSelect
{
    static void Main()
    {
        // 验证根证书签名
        X509Certificate2 x509Root = new X509Certificate2("C:\\Users\\kevin\\Desktop\\KevinRoot.cer");
        Console.WriteLine("Root Certificate Verified?: {0}{1}", x509Root.Verify(), Environment.NewLine);  // 根证书是自签名，所以可以通过。

        X509Certificate2 x509 = new X509Certificate2("C:\\Users\\kevin\\Desktop\\ChildSubject2.cer");

        byte[] rawdata = x509.RawData;
        Console.WriteLine("Content Type: {0}{1}", X509Certificate2.GetCertContentType(rawdata), Environment.NewLine);
        Console.WriteLine("Friendly Name: {0}{1}", x509.FriendlyName, Environment.NewLine);
        Console.WriteLine("Certificate Verified?: {0}{1}", x509.Verify(), Environment.NewLine);
        Console.WriteLine("Simple Name: {0}{1}", x509.GetNameInfo(X509NameType.SimpleName, true), Environment.NewLine);
        Console.WriteLine("Signature Algorithm: {0}{1}", x509.SignatureAlgorithm.FriendlyName, Environment.NewLine);
    //    Console.WriteLine("Private Key: {0}{1}", x509.PrivateKey.ToXmlString(false), Environment.NewLine);  // cer里面并没有私钥信息
        Console.WriteLine("Public Key: {0}{1}", x509.PublicKey.Key.ToXmlString(false), Environment.NewLine);
        Console.WriteLine("Certificate Archived?: {0}{1}", x509.Archived, Environment.NewLine);
        Console.WriteLine("Length of Raw Data: {0}{1}", x509.RawData.Length, Environment.NewLine);


        //Output chain information of the selected certificate.
        X509Chain ch = new X509Chain();
        ch.Build(x509);
        Console.WriteLine("Chain Information");
        ch.ChainPolicy.RevocationMode = X509RevocationMode.Online;
        Console.WriteLine("Chain revocation flag: {0}", ch.ChainPolicy.RevocationFlag);
        Console.WriteLine("Chain revocation mode: {0}", ch.ChainPolicy.RevocationMode);
        Console.WriteLine("Chain verification flag: {0}", ch.ChainPolicy.VerificationFlags);
        Console.WriteLine("Chain verification time: {0}", ch.ChainPolicy.VerificationTime);
        Console.WriteLine("Chain status length: {0}", ch.ChainStatus.Length);
        Console.WriteLine("Chain application policy count: {0}", ch.ChainPolicy.ApplicationPolicy.Count);
        Console.WriteLine("Chain certificate policy count: {0} {1}", ch.ChainPolicy.CertificatePolicy.Count, Environment.NewLine);
        //Output chain element information.
        Console.WriteLine("Chain Element Information");
        Console.WriteLine("Number of chain elements: {0}", ch.ChainElements.Count);
        Console.WriteLine("Chain elements synchronized? {0} {1}", ch.ChainElements.IsSynchronized, Environment.NewLine);

    //    int index = 0;
        foreach (X509ChainElement element in ch.ChainElements)
        {
            Console.WriteLine("Element subject name: {0}", element.Certificate.Subject);
            Console.WriteLine("Element issuer name: {0}", element.Certificate.Issuer);
            Console.WriteLine("Element certificate valid until: {0}", element.Certificate.NotAfter);
            Console.WriteLine("Element certificate is valid: {0}", element.Certificate.Verify());
            Console.WriteLine("Element error status length: {0}", element.ChainElementStatus.Length);
            Console.WriteLine("Element information: {0}", element.Information);
            Console.WriteLine("Number of element extensions: {0}{1}", element.Certificate.Extensions.Count, Environment.NewLine);

            string a = element.Certificate.Thumbprint;
       //     string b = ch.ChainPolicy.ExtraStore[0].Thumbprint;
            //ch.ChainPolicy.ExtraStore[index - 1].Thumbprint;

            if (ch.ChainStatus.Length > 1)
            {
                for (int index = 0; index < element.ChainElementStatus.Length; index++)
                {
                    Console.WriteLine(element.ChainElementStatus[index].Status);
                    Console.WriteLine(element.ChainElementStatus[index].StatusInformation);
                }
            }
        }

        x509.Reset();
        
    }
    
}