Base64实现

最新推荐文章于 2024-12-13 17:20:51 发布

转载最新推荐文章于 2024-12-13 17:20:51 发布 · 47 阅读

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原文链接：http://www.cnblogs.com/stanley198610281217/p/4110374.html

class Base64

{

public:

    static string Encrypt(string sPlainText);

    static string Decrypt(string sCipherText);



private:

    static int ConvertToIndex(unsigned char ucChar);

    static string Algorithm(unsigned char ucByteHigh, unsigned char ucByteMiddle, unsigned char ucByteLow, unsigned char ucAvailableCount);

    static char s_caCharSet[64];

};




char Base64::s_caCharSet[64] =

{

    'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z',

    'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z',

    '0','1','2','3','4','5','6','7','8','9',

    '+','/'

};







int Base64::ConvertToIndex(unsigned char ucChar)

{

    if (ucChar == '+') return 62;

    else if (ucChar == '/') return 63;

    else if (ucChar == '=') return 0;

    else if (ucChar >= 'A' && ucChar <= 'Z')

    {

        return ucChar - 65;

    }

    else if (ucChar >= 'a' && ucChar <= 'z')

    {

        return ucChar - 97 + 26;

    }

    else if (ucChar >= '0' && ucChar <= '9')

    {

        return ucChar - 48 + 26 + 26;

    }

    else

    {

        cerr<<"Base64 convert to Index failed"<<endl;

        return 0; // abort??

    }

}





/**

 * Base64 convert algorithm(from 3 bytes to 4 bytes charset index)

 */

string Base64::Algorithm(unsigned char ucByteHigh, unsigned char ucByteMiddle, unsigned char ucByteLow, unsigned char ucAvailableCount)

{

    string sResult;

    int iTemp = 0;

    unsigned char ucByte1, ucByte2, ucByte3, ucByte4;





    if (ucAvailableCount == 0) return "";



    iTemp = ucByteHigh;

    iTemp <<= 8;



    iTemp |= ucByteMiddle;

    iTemp <<= 8;



    iTemp |= ucByteLow;

    

    ucByte4 = iTemp & 0x3F;

    ucByte3 = (iTemp & 0xFC0) >> 6;

    ucByte2 = (iTemp & 0x3F000) >> 12;

    ucByte1 = (iTemp & 0xFC0000) >> 18;



    if (ucAvailableCount == 1)

    {

        sResult += s_caCharSet[ucByte1];

        sResult += s_caCharSet[ucByte2];

        sResult += "==";

    }

    else if (ucAvailableCount == 2)

    {

        sResult += s_caCharSet[ucByte1];

        sResult += s_caCharSet[ucByte2];

        sResult += s_caCharSet[ucByte3];

        sResult += "=";

    }

    else if (ucAvailableCount == 3)

    {

        sResult += s_caCharSet[ucByte1];

        sResult += s_caCharSet[ucByte2];

        sResult += s_caCharSet[ucByte3];

        sResult += s_caCharSet[ucByte4];

    }

    else

    {

        return "";

    }



    return sResult;

}





/**

 * sPlainText is plaintext that non encrypted

 * return Base64 encrypt text

 */

string Base64::Encrypt(string sPlainText)

{

    string sResult;

    const unsigned int uPlainTextSize = sPlainText.size();

    

    if (sPlainText.empty())

    {

        cerr<<"invalid original text"<<endl;

        return "";

    }

    

    if (uPlainTextSize == 1)

    {

        return Algorithm(sPlainText[0], 0, 0, 1);

    }

    else if (uPlainTextSize == 2)

    {

        return Algorithm(sPlainText[0], sPlainText[1], 0, 2);

    }

    else

    {

        unsigned int i;

        unsigned int uCount = uPlainTextSize / 3 * 3;

        for (i = 0; i < uCount; i+=3)

        {

            string sTmp = Algorithm(sPlainText[i], sPlainText[i+1], sPlainText[i+2], 3);

            sResult += sTmp;

        }



        unsigned int uMore = uPlainTextSize % 3;

        if ( uMore != 0)

        {

            if (uMore == 1)

            {

                sResult += Algorithm(sPlainText[i], 0, 0, 1);

            }

            else

            {

                sResult += Algorithm(sPlainText[i], sPlainText[i+1], 0, 2);

            }

        }

        

        return sResult;

    }

}





/**

 * input ciphertext and return related plaintext

 */

string Base64::Decrypt(string sCipherText)

{

    string sResult;

    

    if (sCipherText.size() % 4 != 0)

    {

        cerr<<"Invalid parameter, Base64 can't convert from ciphertext to plaintext"<<endl;

        return "";

    }



    // from high to low

    unsigned char ucByte1, ucByte2, ucByte3, ucByte4;

    for (unsigned int i = 0; i < sCipherText.size(); i+=4)

    {

        string sTmp;

        int iConvertTo3Bytes = 0;

        ucByte1 = ConvertToIndex(sCipherText[i]);

        ucByte2 = ConvertToIndex(sCipherText[i+1]);

        ucByte3 = ConvertToIndex(sCipherText[i+2]);

        ucByte4 = ConvertToIndex(sCipherText[i+3]);



        iConvertTo3Bytes = ucByte1;

        iConvertTo3Bytes <<= 6;

        iConvertTo3Bytes |= ucByte2;



        iConvertTo3Bytes <<= 6;

        iConvertTo3Bytes |= ucByte3;

        iConvertTo3Bytes <<= 6;

        iConvertTo3Bytes |= ucByte4;



        sTmp = (unsigned char)(iConvertTo3Bytes >> 16);

        

        unsigned char ucTmp = (unsigned char)((iConvertTo3Bytes & 0xFF00) >> 8);

        if (ucTmp == 0)

        {

            sResult += sTmp;

            continue;

        }

        else sTmp += ucTmp;



        ucTmp = (unsigned char)(iConvertTo3Bytes & 0xFF);

        if (ucTmp == 0)

        {

            sResult += sTmp;

            continue;

        }

        else sTmp += ucTmp;



        sResult += sTmp;

    }



    return sResult;

}

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转载于:https://www.cnblogs.com/stanley198610281217/p/4110374.html