C#實現RSA加密解密

RSA介紹

RSA公鑰加密算法是1977年由Ron Rivest、Adi Shamirh和LenAdleman在（美國麻省理工學院）開發的。RSA取名來自開發他們三者的名字。
RSA的缺點:

• 產生密鑰很麻煩，受到素數產生技術的限制，於是難以作到一次一密。

• 分組長度太大，爲保證安全性，n 至少也要 600bits以上，使運算代價很高，尤爲是速度較慢，較對稱密碼算法慢幾個數量級；且隨着大數分解技術的發展，這個長度還在增長，不利於數據格式的標準化。目前，SET(Secure Electronic Transaction)協議中要求CA採用2048bits長的密鑰，其餘實體使用1024比特的密鑰。C)RSA密鑰長度隨着保密級別提升，增長很快。下表列出了對同一安全級別所對應的密鑰長度。

  保密級別	對稱密鑰長度（bit）	RSA密鑰長度（bit）	ECC密鑰長度（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的相關操做

• 生成公鑰和私鑰

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);
    }
}

/// <summary>
/// generate RSA secret key
/// </summary>
/// <param name="keySize">the size of the key,must from 384 bits to 16384 bits in increments of 8 </param>
/// <returns></returns>
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;
}

• 實現公鑰加密私鑰解密

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;
}

密鑰格式的轉換

C#中RSA公鑰和私鑰的格式都是XML的,而在其餘語言如java中,生成的RSA密鑰就是普通的Base64字符串,因此須要將C#xml格式的密鑰轉換成普通的Base64字符串,同時也要實現Base64密鑰字符串生成C#中xml格式的密鑰.
安裝 BouncyCastle 這個Nuget包
PM > Install-Package BouncyCastle
BouncyCastle項目網址
BouncyCastlegithub地址
構造一個RSAKeyConventer類

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
    {
        /// <summary>
        /// xml private key -> base64 private key string
        /// </summary>
        /// <param name="xmlPrivateKey"></param>
        /// <returns></returns>
        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;
        }

        /// <summary>
        /// xml public key -> base64 public key string
        /// </summary>
        /// <param name="xmlPublicKey"></param>
        /// <returns></returns>
        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;
        }

        /// <summary>
        /// base64 private key string -> xml private key
        /// </summary>
        /// <param name="privateKey"></param>
        /// <returns></returns>
        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);
            }
        }

        /// <summary>
        /// base64 public key string -> xml public key
        /// </summary>
        /// <param name="pubilcKey"></param>
        /// <returns></returns>
        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);
            }
        }
    }
}