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  • 关于RSA加密算法的长度限制问题

    RSA是常用的非对称加密算法。近来有学生在项目中使用System.Security类库中的RSA加密算法时,出现了“不正确的长度”,这实际上是因为待加密的数据超长所致。.net
    Framework中提供的RSA算法规定,每次加密的字节数,不能超过密钥的长度值减去11,而每次加密得到的密文长度,却恰恰是密钥的长度。所以,如果要加密较长的数据,可以采用数据截取的方法,分段加密,实现如下:


           RSACryptoServiceProvider rsa = new
    RSACryptoServiceProvider();


           byte[] data = ........;        
    //要加密的数据


           string publicKey = .... ;  //获取公钥


           rsa.FromXmlString(publicKey);


           int keySize = rsa.KeySize / 8;


           int bufferSize = keySize - 11;


           byte[] buffer = new
    byte[bufferSize];


           MemoryStream msInput = new
    MemoryStream(data);


           MemoryStream msOuput = new
    MemoryStream();


           int readLen = msInput.Read(buffer, 0,
    bufferSize);


           while(readLen > 0)


           {


                   byte[] dataToEnc = new
    byte[readLen];


                   Array.Copy(buffer, 0 , dataToEnc,
    0, readLen);


                   byte[] encData =
    rsa.Encrypt(dataToEnc , false);


                   msOutput.Write(encData, 0,
    encData.Length);


                   readLen = msInput.Read(buffer, 0,
    bufferSize);


           }


           msInput.Close();


           byte[] result = msOutput.ToArray();   
    //得到加密结果


           msOutput.Close();


           rsa.Clear();



    解密时肯定也要使用分段解密,算法如下:


           RSACryptoServiceProvider rsa = new
    RSACryptoServiceProvider();


           byte[] key = .....;    //加载私钥
           string privateKey =
    Encoding.ASCII.GetString(key);
           byte[] dataEnc = ...;   //加载密文


           rsa.FromXmlString(privateKey);


           int keySize = rsa.KeySize / 8;


           byte[]
    buffer = new byte[keySize];


           MemoryStream msInput = new
    MemoryStream(dataEnc );


           MemoryStream msOuput = new
    MemoryStream();


           int readLen = msInput.Read(buffer, 0,
    keySize);


           while(readLen > 0)


           {


                   byte[] dataToDec = new
    byte[readLen];


                   Array.Copy(buffer, 0 , dataToDec,
    0, readLen);


                   byte[] decData =
    rsa.Decrypt(dataToDec , false);


                   msOutput.Write(decData, 0,
    decData.Length);


                   readLen = msInput.Read(buffer, 0,
    keySize);


           }


           msInput.Close();


           byte[] result = msOutput.ToArray();   
    //得到解密结果


           msOutput.Close();


           rsa.Clear();

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  • 原文地址:https://www.cnblogs.com/zjoch/p/2687247.html
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