C#实现RSA加密解密

RSA介绍

RSA公钥加密算法是1977年由Ron Rivest、Adi Shamirh和LenAdleman在（美国麻省理工学院）开发的。RSA取名来自开发他们三者的名字。
RSA的缺点:

• 产生密钥很麻烦，受到素数产生技术的限制，因而难以做到一次一密。

• 分组长度太大，为保证安全性，n 至少也要 600bits以上，使运算代价很高，尤其是速度较慢，较对称密码算法慢几个数量级；且随着大数分解技术的发展，这个长度还在增加，不利于数据格式的标准化。目前，SET(Secure Electronic Transaction)协议中要求CA采用2048bits长的密钥，其他实体使用1024比特的密钥。C)RSA密钥长度随着保密级别提高，增加很快。下表列出了对同一安全级别所对应的密钥长度。

  保密级别	对称密钥长度（bit）	RSA密钥长度（bit）	ECC密钥长度（bit）	保密年限
  80	80	1024	160	2010
  112	112	2048	224	2030
  128	128	3072	256	2040
  192	192	7680	384	2080
  256	256	15360	512	2120

C#中RSA的相关操作

• 生成公钥和私钥

struct RSASecretKey
{
    public RSASecretKey(string privateKey, string publicKey)
    {
        PrivateKey = privateKey;
        PublicKey = publicKey;
    }
    public string PublicKey { get; set; }
    public string PrivateKey { get; set; }
    public override string ToString()
    {
        return string.Format(
            "PrivateKey: {0}\r\nPublicKey: {1}", PrivateKey, PublicKey);
    }
}

/// 

/// generate RSA secret key
/// 
/// the size of the key,must from 384 bits to 16384 bits in increments of 8 
/// 
RSASecretKey GenerateRSASecretKey(int keySize)
{
    RSASecretKey rsaKey = new RSASecretKey();
    using (RSACryptoServiceProvider rsa = new RSACryptoServiceProvider(keySize))
    {
        rsaKey.PrivateKey = rsa.ToXmlString(true);
        rsaKey.PublicKey = rsa.ToXmlString(false);
    }
    return rsaKey;
}

• 实现公钥加密私钥解密

string RSAEncrypt(string xmlPublicKey,string content)
{
    string encryptedContent = string.Empty;
    using(RSACryptoServiceProvider rsa = new RSACryptoServiceProvider())
    {
        rsa.FromXmlString(xmlPublicKey);
        byte[] encryptedData = rsa.Encrypt(Encoding.Default.GetBytes(content), false);
        encryptedContent = Convert.ToBase64String(encryptedData);
    }
    return encryptedContent;
}

string RSADecrypt(string xmlPrivateKey, string content)
{
    string decryptedContent = string.Empty;
    using (RSACryptoServiceProvider rsa = new RSACryptoServiceProvider())
    {
        rsa.FromXmlString(xmlPrivateKey);
        byte[] decryptedData = rsa.Decrypt(Convert.FromBase64String(content), false);
        decryptedContent = Encoding.GetEncoding("gb2312").GetString(decryptedData);
    }
    return decryptedContent;
}

密钥格式的转换

C#中RSA公钥和私钥的格式都是XML的,而在其他语言如java中,生成的RSA密钥就是普通的Base64字符串,所以需要将C#xml格式的密钥转换成普通的Base64字符串,同时也要实现Base64密钥字符串生成C#中xml格式的密钥.
安装 BouncyCastle 这个Nuget包
PM > Install-Package BouncyCastle
BouncyCastle项目网址
BouncyCastlegithub地址
构造一个RSAKeyConventer类

namespace RSA
{
    using System;
    using System.Security.Cryptography;
    using Org.BouncyCastle.Asn1.Pkcs;
    using Org.BouncyCastle.Math;
    using Org.BouncyCastle.Pkcs;
    using Org.BouncyCastle.Asn1.X509;
    using Org.BouncyCastle.X509;
    using Org.BouncyCastle.Security;
    using Org.BouncyCastle.Crypto.Parameters;

    public class RSAKeyConverter
    {
        /// 

        /// xml private key -> base64 private key string
        /// 
        /// 
        /// 
        public static string FromXmlPrivateKey(string xmlPrivateKey)
        {
            string result = string.Empty;
            using(RSACryptoServiceProvider rsa = new RSACryptoServiceProvider())
            {
                rsa.FromXmlString(xmlPrivateKey);
                RSAParameters param = rsa.ExportParameters(true);
                RsaPrivateCrtKeyParameters privateKeyParam = new RsaPrivateCrtKeyParameters(
                    new BigInteger(1, param.Modulus), new BigInteger(1, param.Exponent),
                    new BigInteger(1, param.D), new BigInteger(1, param.P),
                    new BigInteger(1, param.Q), new BigInteger(1, param.DP),
                    new BigInteger(1, param.DQ), new BigInteger(1, param.InverseQ));
                PrivateKeyInfo privateKey = PrivateKeyInfoFactory.CreatePrivateKeyInfo(privateKeyParam);
               
                result = Convert.ToBase64String(privateKey.ToAsn1Object().GetEncoded());
            }
            return result;
        }

        /// 

        /// xml public key -> base64 public key string
        /// 
        /// 
        /// 
        public static string FromXmlPublicKey(string xmlPublicKey)
        {
            string result = string.Empty;
            using(RSACryptoServiceProvider rsa = new RSACryptoServiceProvider())
            {
                rsa.FromXmlString(xmlPublicKey);
                RSAParameters p = rsa.ExportParameters(false);
                RsaKeyParameters keyParams = new RsaKeyParameters(
                    false, new BigInteger(1,p.Modulus), new BigInteger(1, p.Exponent));
                SubjectPublicKeyInfo publicKeyInfo = SubjectPublicKeyInfoFactory.CreateSubjectPublicKeyInfo(keyParams);
                result = Convert.ToBase64String(publicKeyInfo.ToAsn1Object().GetEncoded());
            }
            return result;
        }

        /// 

        /// base64 private key string -> xml private key
        /// 
        /// 
        /// 
        public static string ToXmlPrivateKey(string privateKey)
        {
            RsaPrivateCrtKeyParameters privateKeyParams =
                PrivateKeyFactory.CreateKey(Convert.FromBase64String(privateKey)) as RsaPrivateCrtKeyParameters;
            using(RSACryptoServiceProvider rsa = new RSACryptoServiceProvider())
            {
                RSAParameters rsaParams = new RSAParameters()
                {
                    Modulus = privateKeyParams.Modulus.ToByteArrayUnsigned(),
                    Exponent = privateKeyParams.PublicExponent.ToByteArrayUnsigned(),
                    D = privateKeyParams.Exponent.ToByteArrayUnsigned(),
                    DP = privateKeyParams.DP.ToByteArrayUnsigned(),
                    DQ = privateKeyParams.DQ.ToByteArrayUnsigned(),
                    P = privateKeyParams.P.ToByteArrayUnsigned(),
                    Q = privateKeyParams.Q.ToByteArrayUnsigned(),
                    InverseQ = privateKeyParams.QInv.ToByteArrayUnsigned()
                };
                rsa.ImportParameters(rsaParams);
                return rsa.ToXmlString(true);
            }
        }

        /// 

        /// base64 public key string -> xml public key
        /// 
        /// 
        /// 
        public static string ToXmlPublicKey(string pubilcKey)
        {
            RsaKeyParameters p = 
                PublicKeyFactory.CreateKey(Convert.FromBase64String(pubilcKey)) as RsaKeyParameters;
            using(RSACryptoServiceProvider rsa = new RSACryptoServiceProvider())
            {
                RSAParameters rsaParams = new RSAParameters
                {
                    Modulus = p.Modulus.ToByteArrayUnsigned(),
                    Exponent = p.Exponent.ToByteArrayUnsigned()
                };
                rsa.ImportParameters(rsaParams);
                return rsa.ToXmlString(false);
            }
        }
    }
}