Base64实现

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;}