RSA非对称加密算法实现：C#

　　RSA是1977年由罗纳德·李维斯特（Ron Rivest）、阿迪·萨莫尔（Adi Shamir）和伦纳德·阿德曼（Leonard Adleman）一起提出的。当时他们三人都在麻省理工学院工作。RSA就是他们三人姓氏开头字母拼在一起组成的。

　　RSA解决了对称加密的一个不足，比如AES算法加密和解密时使用的是同一个秘钥，因此这个秘钥不能公开，因此对于需要公开秘钥的场合，我们需要在加密和解密过程中使用不同的秘钥，加密使用的公钥可以公开，解密使用的私钥要保密，这就是非对称加密的好处。　

　　常用的开发语言来实现RSA加密：

　　RSA非对称加密算法实现：Java

　　RSA非对称加密算法实现：C#

　　RSA非对称加密算法实现：Golang

　　RSA非对称加密算法实现：Python

　

　　公钥与私钥

　　公钥与私钥是成对的，一般的，我们认为的是公钥加密、私钥解密、私钥签名、公钥验证，有人说成私钥加密，公钥解密时不对的。

　　公钥与私钥的生成有多种方式，可以通过程序生成（下文具体实现），可以通过openssl工具：　　

    # 生成一个私钥，推荐使用1024位的秘钥，秘钥以pem格式保存到-out参数指定的文件中，采用PKCS1格式
    openssl genrsa -out rsa.pem 1024 
    # 生成与私钥对应的公钥，生成的是Subject Public Key，一般配合PKCS8格式私钥使用
    openssl rsa -in rsa.pem -pubout -out rsa.pub  

　　RSA生成公钥与私钥一般有两种格式：PKCS1和PKCS8，上面的命令生成的秘钥是PKCS1格式的，而公钥是Subject Public Key，一般配合PKCS8格式私钥使用，所以就可能会涉及到PKCS1和PKCS8之间的转换：

    # PKCS1格式私钥转换为PKCS8格式私钥，私钥直接输出到-out参数指定的文件中
    openssl pkcs8 -topk8 -inform PEM -in rsa.pem -outform pem -nocrypt -out rsa_pkcs8.pem
    # PKCS8格式私钥转换为PKCS1格式私钥，私钥直接输出到-out参数指定的文件中
    openssl rsa -in rsa_pkcs8.pem -out rsa_pkcs1.pem

    # PKCS1格式公钥转换为PKCS8格式公钥，转换后的内容直接输出
    openssl rsa -pubin -in rsa.pub -RSAPublicKey_out
    # PKCS8格式公钥转换为PKCS1格式公钥，转换后的内容直接输出
    openssl rsa -RSAPublicKey_in -pubout -in rsa.pub

　　现实中，我们往往从pem、crt、pfx文件获取公私和私钥，crt、pfx的制作可以参考：简单的制作ssl证书，并在nginx和IIS中使用，或者使用现成的：https://pan.baidu.com/s/1MJ5YmuZiLBnf-DfNR_6D7A (提取码：c6tj)，密码都是：123456

　　C#实现

　　为了方便读取pem、crt、pfx文件中的公私和私钥，这里我使用了第三方的包：Portable.BouncyCastle，可以使用NuGet安装：Install-Package Portable.BouncyCastle

　　接着，这里我封装了一个RsaHelper辅助类来实现各种RSA加密的过程：　　

　　

using Org.BouncyCastle.Utilities.IO.Pem;
using System;
using System.Collections.Generic;
using System.IO;
using System.Security.Cryptography;
using System.Security.Cryptography.X509Certificates;
using System.Text;

namespace ConsoleApp1
{
    public class RsaHelper
    {

        #region key
        /// <summary>
        /// 将秘钥保存到Pem文件
        /// </summary>
        /// <param name="isPrivateKey"></param>
        /// <param name="buffer"></param>
        /// <param name="pemFileName"></param>
        /// <returns></returns>
        public static void WriteToPem(byte[] buffer, bool isPrivateKey, string pemFileName)
        {
            PemObject pemObject = new PemObject(isPrivateKey ? "RSA PRIVATE KEY" : "RSA PUBLIC KEY", buffer);
            if (File.Exists(pemFileName))
            {
                File.Delete(pemFileName);
            }
            using (var fileStream = new FileStream(pemFileName, FileMode.OpenOrCreate, FileAccess.Write))
            {
                using (var sw = new StreamWriter(fileStream))
                {
                    var writer = new PemWriter(sw);
                    writer.WriteObject(pemObject);
                    sw.Flush();
                }
            }
        }
        /// <summary>
        /// 从Pem文件中读取秘钥
        /// </summary>
        /// <param name="pemFileName"></param>
        /// <returns></returns>
        public static byte[] ReadFromPem(string pemFileName)
        {
            using (var fileStream = new FileStream(pemFileName, FileMode.Open, FileAccess.Read))
            {
                using (var sw = new StreamReader(fileStream))
                {
                    var writer = new PemReader(sw);
                    return writer.ReadPemObject().Content;
                }
            }
        }

        /// <summary>
        /// 从xml中读取秘钥
        /// </summary>
        /// <param name="xml"></param>
        /// <param name="isPrivateKey"></param>
        /// <param name="usePkcs8"></param>
        /// <returns></returns>
        public static byte[] ReadFromXml(string xml, bool isPrivateKey, bool usePkcs8)
        {
            using (var rsa = new RSACryptoServiceProvider())
            {
                rsa.FromXmlString(xml);
                if (isPrivateKey)
                {
                    return usePkcs8 ? rsa.ExportPkcs8PrivateKey() : rsa.ExportRSAPrivateKey();
                }
                return usePkcs8 ? rsa.ExportSubjectPublicKeyInfo() : rsa.ExportRSAPublicKey();
            }
        }
        /// <summary>
        /// 将秘钥保存到xml中
        /// </summary>
        /// <param name="buffer"></param>
        /// <param name="isPrivateKey"></param>
        /// <param name="usePkcs8"></param>
        /// <returns></returns>
        public static string WriteToXml(byte[] buffer, bool isPrivateKey, bool usePkcs8)
        {
            using (var rsa = CreateRSACryptoServiceProvider(buffer, isPrivateKey, usePkcs8))
            {
                return rsa.ToXmlString(isPrivateKey);
            }
        }

        /// <summary>
        /// 获取RSA非对称加密的Key
        /// </summary>
        /// <param name="publicKey"></param>
        /// <param name="privateKey"></param>
        public static void GenerateRsaKey(bool usePKCS8, out byte[] publicKey, out byte[] privateKey)
        {
            using (RSACryptoServiceProvider rsa = new RSACryptoServiceProvider())
            {
                rsa.KeySize = 1024;//1024位
                if (usePKCS8)
                {
                    //使用pkcs8填充方式导出
                    publicKey = rsa.ExportSubjectPublicKeyInfo();//公钥
                    privateKey = rsa.ExportPkcs8PrivateKey();//私钥
                }
                else
                {
                    //使用pkcs1填充方式导出
                    publicKey = rsa.ExportRSAPublicKey();//公钥
                    privateKey = rsa.ExportRSAPrivateKey();//私钥
                }
            }
        }
        /// <summary>
        /// 从Pfx文件获取RSA非对称加密的Key
        /// </summary>
        /// <param name="pfxFileName"></param>
        /// <param name="publicKey"></param>
        /// <param name="privateKey"></param>
        public static void ReadFromPfx(string pfxFileName, string password, out byte[] publicKey, out byte[] privateKey)
        {
            X509Certificate2 x509Certificate2 = new X509Certificate2(pfxFileName, password, X509KeyStorageFlags.Exportable);
            publicKey = x509Certificate2.GetRSAPublicKey().ExportRSAPublicKey();
            privateKey = x509Certificate2.GetRSAPrivateKey().ExportRSAPrivateKey();
        }
        /// <summary>
        /// 从Crt文件中读取公钥
        /// </summary>
        /// <param name="crtFileName"></param>
        /// <param name="password"></param>
        /// <returns></returns>
        public static byte[] ReadPublicKeyFromCrt(string crtFileName, string password)
        {
            X509Certificate2 x509Certificate2 = new X509Certificate2(crtFileName, password, X509KeyStorageFlags.Exportable);
            var publicKey = x509Certificate2.GetRSAPublicKey().ExportRSAPublicKey();
            return publicKey;
        }
        #endregion

        #region Pkcs1 and Pkcs8

        /// <summary>
        /// Pkcs1转Pkcs8
        /// </summary>
        /// <param name="isPrivateKey"></param>
        /// <param name="buffer"></param>
        /// <returns></returns>
        public static byte[] Pkcs1ToPkcs8(bool isPrivateKey, byte[] buffer)
        {
            using (var rsa = new RSACryptoServiceProvider())
            {
                if (isPrivateKey)
                {
                    rsa.ImportRSAPrivateKey(buffer, out _);
                    return rsa.ExportPkcs8PrivateKey();
                }
                else
                {
                    rsa.ImportRSAPublicKey(buffer, out _);
                    return rsa.ExportSubjectPublicKeyInfo();
                }
            }
        }
        /// <summary>
        /// Pkcs8转Pkcs1
        /// </summary>
        /// <param name="isPrivateKey"></param>
        /// <param name="buffer"></param>
        /// <returns></returns>
        public static byte[] Pkcs8ToPkcs1(bool isPrivateKey, byte[] buffer)
        {
            using (var rsa = new RSACryptoServiceProvider())
            {
                if (isPrivateKey)
                {
                    rsa.ImportPkcs8PrivateKey(buffer, out _);
                    return rsa.ExportRSAPrivateKey();
                }
                else
                {
                    rsa.ImportSubjectPublicKeyInfo(buffer, out _);
                    return rsa.ExportRSAPublicKey();
                }
            }
        }

        #endregion

        #region RSA

        /// <summary>
        /// 获取一个RSACryptoServiceProvider
        /// </summary>
        /// <param name="isPrivateKey"></param>
        /// <param name="buffer"></param>
        /// <param name="usePkcs8"></param>
        /// <returns></returns>
        public static RSACryptoServiceProvider CreateRSACryptoServiceProvider(byte[] buffer, bool isPrivateKey, bool usePkcs8 = false)
        {
            RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
            if (isPrivateKey)
            {
                if (usePkcs8)
                    rsa.ImportPkcs8PrivateKey(buffer, out _);
                else
                    rsa.ImportRSAPrivateKey(buffer, out _);
            }
            else
            {
                if (usePkcs8)
                    rsa.ImportSubjectPublicKeyInfo(buffer, out _);
                else
                    rsa.ImportRSAPublicKey(buffer, out _);
            }
            return rsa;
        }

        /// <summary>
        /// RSA公钥加密
        /// </summary>
        /// <param name="value">待加密的明文</param>
        /// <param name="publicKey">公钥</param>
        /// <param name="usePkcs8">是否使用pkcs8填充</param>
        /// <returns></returns>
        public static string RsaEncrypt(string value, byte[] publicKey, bool usePkcs8 = false)
        {
            if (string.IsNullOrEmpty(value)) return value;

            using (RSACryptoServiceProvider rsa = CreateRSACryptoServiceProvider(publicKey, false, usePkcs8))
            {
                var buffer = Encoding.UTF8.GetBytes(value);
                buffer = rsa.Encrypt(buffer, false);

                //使用hex格式输出数据
                StringBuilder result = new StringBuilder();
                foreach (byte b in buffer)
                {
                    result.AppendFormat("{0:x2}", b);
                }
                return result.ToString();
                //或者使用下面的输出
                //return BitConverter.ToString(buffer).Replace("-", "").ToLower();
            }
        }
        /// <summary>
        /// RSA私钥解密
        /// </summary>
        /// <param name="value">密文</param>
        /// <param name="privateKey">私钥</param>
        /// <param name="usePkcs8">是否使用pkcs8填充</param>
        /// <returns></returns>
        public static string RsaDecrypt(string value, byte[] privateKey, bool usePkcs8 = false)
        {
            if (string.IsNullOrEmpty(value)) return value;

            using (RSACryptoServiceProvider rsa = CreateRSACryptoServiceProvider(privateKey, true, usePkcs8))
            {
                //转换hex格式数据为byte数组
                var buffer = new byte[value.Length / 2];
                for (var i = 0; i < buffer.Length; i++)
                {
                    buffer[i] = (byte)Convert.ToInt32(value.Substring(i * 2, 2), 16);
                }
                buffer = rsa.Decrypt(buffer, false);
                return Encoding.UTF8.GetString(buffer);
            }
        }
        /// <summary>
        /// RSA私钥生成签名
        /// </summary>
        /// <param name="value">原始值</param>
        /// <param name="publicKey">公钥</param>
        /// <param name="halg">签名hash算法：SHA，SHA1，MD5，SHA256，SHA384，SHA512</param>
        /// <param name="usePkcs8">是否使用pkcs8填充</param>
        /// <returns></returns>
        public static string Sign(string value, byte[] privateKey, string halg = "MD5", bool usePkcs8 = false)
        {
            if (string.IsNullOrEmpty(value)) return value;

            using (RSACryptoServiceProvider rsa = CreateRSACryptoServiceProvider(privateKey, true, usePkcs8))
            {
                byte[] buffer = Encoding.UTF8.GetBytes(value);
                buffer = rsa.SignData(buffer, HashAlgorithm.Create(halg));

                //使用hex格式输出数据
                StringBuilder result = new StringBuilder();
                foreach (byte b in buffer)
                {
                    result.AppendFormat("{0:x2}", b);
                }
                return result.ToString();
                //或者使用下面的输出
                //return BitConverter.ToString(buffer).Replace("-", "").ToLower();
            }
        }
        /// <summary>
        /// RSA公钥验证签名
        /// </summary>
        /// <param name="value">原始值</param>
        /// <param name="publicKey">公钥</param>
        /// <param name="signature">签名</param>
        /// <param name="halg">签名hash算法：SHA，SHA1，MD5，SHA256，SHA384，SHA512</param>
        /// <param name="usePkcs8">是否使用pkcs8填充</param>
        /// <returns></returns>
        public static bool Verify(string value, byte[] publicKey, string signature, string halg = "MD5", bool usePkcs8 = false)
        {
            if (string.IsNullOrEmpty(value)) return false;

            using (RSACryptoServiceProvider rsa = CreateRSACryptoServiceProvider(publicKey, false, usePkcs8))
            {
                //转换hex格式数据为byte数组
                var buffer = new byte[signature.Length / 2];
                for (var i = 0; i < buffer.Length; i++)
                {
                    buffer[i] = (byte)Convert.ToInt32(signature.Substring(i * 2, 2), 16);
                }
                return rsa.VerifyData(Encoding.UTF8.GetBytes(value), HashAlgorithm.Create(halg), buffer);
            }
        }
        #endregion
    }
}

　　可以使用生成RSA的公私秘钥：　　

    //通过程序生成
    RsaHelper.GenerateRsaKey(usePKCS8, out publicKey, out privateKey);

　　生成秘钥后，需要保存，一般保存到pem文件中：　　

    //保存到Pem文件，filePath是文件目录
    RsaHelper.WriteToPem(publicKey, false, Path.Combine(filePath, "rsa.pub"));
    RsaHelper.WriteToPem(privateKey, true, Path.Combine(filePath, "rsa.pem"));

　　还以将公钥和私钥输出为xml格式:　　

    //保存到xml中
    string publicKeyXml = RsaHelper.WriteToXml(publicKey, false, usePKCS8);
    string privateKeyXml = RsaHelper.WriteToXml(privateKey, true, usePKCS8);

　　保存到pem文件和xml中后，也可以从中读取：　　

    //从Pem文件获取，filePath是文件目录
    publicKey = RsaHelper.ReadFromPem(Path.Combine(filePath, "rsa.pub"));
    privateKey = RsaHelper.ReadFromPem(Path.Combine(filePath, "rsa.pem"));

    //从xml中读取
    publicKey = RsaHelper.ReadFromXml(publicKeyXml, false, usePKCS8);
    privateKey = RsaHelper.ReadFromXml(privateKeyXml, true, usePKCS8);

　　还可以从crt证书中读取公钥，而crt文件不包含私钥，因此需要单独获取私钥：

    //从crt文件读取，filePath是文件目录
    publicKey = RsaHelper.ReadPublicKeyFromCrt(Path.Combine(filePath, "demo.crt"), "");
    privateKey = RsaHelper.ReadFromPem(Path.Combine(filePath, "demo.key"));

　　pfx文件中包含了公钥和私钥，可以很方便就读取到：　　

    //从demo.pfx文件读取（demo.pfx采用的是pkcs1），filePath是文件目录
    RsaHelper.ReadFromPfx(Path.Combine(filePath, "demo.pfx"), "123456", out publicKey, out privateKey);

　　有时候我们还可能需要进行秘钥的转换：　　

    // Pkcs8格式公钥转换为Pkcs1格式公钥
    publicKey = RsaHelper.Pkcs8ToPkcs1(false, publicKey);
    // Pkcs8格式私钥转换为Pkcs1格式私钥
    privateKey = RsaHelper.Pkcs8ToPkcs1(true, privateKey);
    // Pkcs1格式公钥转换为Pkcs8格式公钥
    publicKey = RsaHelper.Pkcs1ToPkcs8(false, publicKey);
    // Pkcs1格式私钥转换为Pkcs8格式私钥
    privateKey = RsaHelper.Pkcs1ToPkcs8(true, privateKey);

　　有了公钥和私钥，接下就就能实现加密、解密、签名、验证签名等操作了：　　

    string encryptText = RsaHelper.RsaEncrypt(text, publicKey, usePKCS8);
    Console.WriteLine($"【{text}】经过【RSA】加密后：{encryptText}");

    string decryptText = RsaHelper.RsaDecrypt(encryptText, privateKey, usePKCS8);
    Console.WriteLine($"【{encryptText}】经过【RSA】解密后：{decryptText}");

    string signature = RsaHelper.Sign(text, privateKey, "MD5", usePKCS8);
    Console.WriteLine($"【{text}】经过【RSA】签名后：{signature}");

    bool result = RsaHelper.Verify(text, publicKey, signature, "MD5", usePKCS8);
    Console.WriteLine($"【{text}】的签名【{signature}】经过【RSA】验证后结果是：{result}");

　　完整的demo代码：　　

    using System;
    using System.IO;
    
    namespace ConsoleApp1
    {
        class Program
        {
            static void Main(string[] args)
            {
                string text = "上山打老虎";
                bool usePKCS8 = true;// usePKCS8=true表示是否成PKCS8格式的公私秘钥,否则乘车PKCS1格式的公私秘钥
                string filePath = Directory.GetCurrentDirectory();
                Console.WriteLine($"文件路径：{filePath}");// 存放pem,crt,pfx等文件的目录
                byte[] publicKey, privateKey;// 公钥和私钥
    
                //通过程序生成
                RsaHelper.GenerateRsaKey(usePKCS8, out publicKey, out privateKey);
                //从Pem文件获取，filePath是文件目录
                //publicKey = RsaHelper.ReadFromPem(Path.Combine(filePath, "rsa.pub"));
                //privateKey = RsaHelper.ReadFromPem(Path.Combine(filePath, "rsa.pem"));
    
                //从demo.pfx文件读取（demo.pfx采用的是pkcs1），filePath是文件目录
                //RsaHelper.ReadFromPfx(Path.Combine(filePath, "demo.pfx"), "123456", out publicKey, out privateKey);
                //从crt文件读取，filePath是文件目录
                //publicKey = RsaHelper.ReadPublicKeyFromCrt(Path.Combine(filePath, "demo.crt"), "");
                //privateKey = RsaHelper.ReadFromPem(Path.Combine(filePath, "demo.key"));
    
                //保存到Pem文件，filePath是文件目录
                RsaHelper.WriteToPem(publicKey, false, Path.Combine(filePath, "rsa.pub"));
                RsaHelper.WriteToPem(privateKey, true, Path.Combine(filePath, "rsa.pem"));
    
                //保存到xml中
                string publicKeyXml = RsaHelper.WriteToXml(publicKey, false, usePKCS8);
                string privateKeyXml = RsaHelper.WriteToXml(privateKey, true, usePKCS8);
    
                //从xml中读取
                publicKey = RsaHelper.ReadFromXml(publicKeyXml, false, usePKCS8);
                privateKey = RsaHelper.ReadFromXml(privateKeyXml, true, usePKCS8);
    
                // Pkcs8格式公钥转换为Pkcs1格式公钥
                publicKey = RsaHelper.Pkcs8ToPkcs1(false, publicKey);
                // Pkcs8格式私钥转换为Pkcs1格式私钥
                privateKey = RsaHelper.Pkcs8ToPkcs1(true, privateKey);
                // Pkcs1格式公钥转换为Pkcs8格式公钥
                publicKey = RsaHelper.Pkcs1ToPkcs8(false, publicKey);
                // Pkcs1格式私钥转换为Pkcs8格式私钥
                privateKey = RsaHelper.Pkcs1ToPkcs8(true, privateKey);
    
                string encryptText = RsaHelper.RsaEncrypt(text, publicKey, usePKCS8);
                Console.WriteLine($"【{text}】经过【RSA】加密后：{encryptText}");
    
                string decryptText = RsaHelper.RsaDecrypt(encryptText, privateKey, usePKCS8);
                Console.WriteLine($"【{encryptText}】经过【RSA】解密后：{decryptText}");
    
                string signature = RsaHelper.Sign(text, privateKey, "MD5", usePKCS8);
                Console.WriteLine($"【{text}】经过【RSA】签名后：{signature}");
    
                bool result = RsaHelper.Verify(text, publicKey, signature, "MD5", usePKCS8);
                Console.WriteLine($"【{text}】的签名【{signature}】经过【RSA】验证后结果是：{result}");
            }
        }
    }