[C++]实现base64加密算法和解密算法

 1 string deciToBin(int deci)                                //10进制转2进制函数
 2 {
 3 
 4     string hexStr(8, ' ' );
 5     int Value = 0;
 6     int i = 0;
 7 
 8     for (; deci != 0; ++i, deci /= 2)
 9     {
10         Value = deci % 2;
11         hexStr.at(i) =  Value + '0';
12     }
13 
14     hexStr = hexStr.substr(0, i);
15 
16     reverse(hexStr.begin(), hexStr.end());
17 
18     if (hexStr.length() < 8)
19     {
20         string add( 8 - hexStr.length(), '0');
21         hexStr = add + hexStr;
22     }
23 
24     return hexStr;
25 }

 1 string base64_encryption(const string in)                //加密函数
 2 {
 3     int i = 0;                            //总的控制变量
 4     int k = 0;                          //24位(4个6位)控制变量
 5     const int n = in.length();     //二进制序列长度
 6     string subs;                        //要对应输出的子串
 7     string out;                        //输出结果字符串
 8     string value("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/");       //对应字符
 9 
10     while (n - i >= 24)            //处理完整的三个字节
11     {
12         for (k = 0; k < 4; ++k)
13         {
14             subs = in.substr( i + k * 6, 6);            //取出6位
15 
16             int sum = 0;
17             int j = 0;
18 
19             for (auto & x : subs)
20             {
21                 sum += (x - '0') * pow(2, 5 - j);
22                 ++j;
23             }                                                                            //得到下标
24 
25             out +=  value.at(sum);                                          //输出对应字符
26         }
27 
28         i += 24;                                                                    //前进24位
29 
30         if ( i % 76 == 0)
31             cout << endl;
32     }
33 
34     if ( i != n)                                                                       //处理剩下的不足24位部分
35     {
36         int charlen;                                              //剩下的长度
37 
38         if ((n - i) % 6 == 0)
39             charlen = (n - i) / 6;
40         else
41             charlen = (n - i) / 6 + 1;
42 
43         for (k = 0; k < charlen; ++k)
44         {
45             subs = in.substr( i + k * 6, i + (k + 1) * 6 - 1);            //取出6位
46 
47             int sum = 0;
48             int j = 0;
49 
50             for (auto & x : subs)
51             {
52                 sum += (x - '0') * pow(2, 5 - j);
53                 ++j;
54             }                                                                            //得到下标
55 
56             out +=  value.at(sum);                                            //输出对应字符
57         }
58 
59         if ((n - i) % 16 == 0)
60             out += "=";
61 
62         else
63             out += "==";
64 
65     }
66 
67     return out;
68 }

 1 string base64_decryption(const string in)
 2 {
 3     string value("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/");
 4     string out0;
 5     string out1;
 6     string deciToBin_6bit(int);
 7 
 8     for( auto x = in.cbegin(); (*x) != '=' && x != in.cend(); ++x)    //排除等号
 9         out0 += deciToBin_6bit(value.find(*x));
10 
11     const int n = out0.length();
12 
13     for(int i = 0; i < n; i += 8)           //每8位提取一次
14     {
15         string subs = out0.substr(i, 8);    //提取8位
16         int j = 0;
17         int sum = 0;
18 
19         for(auto &x : subs)
20         {
21             sum += (x - '0') * pow(2, 7 - j);
22             ++j;
23         }                                   //按权展开，得到ASCII码
24 
25         out1 += static_cast<char>(sum);     //转换为相应字符
26     }
27 
28     return out1;
29 
30 }

 1 string deciToBin_6bit(int deci)                                //10进制转2进制函数
 2 {
 3 
 4     string hexStr(6, ' ' );
 5     int Value = 0;
 6     int i = 0;
 7 
 8     for (; deci != 0; ++i, deci /= 2)
 9     {
10         Value = deci % 2;
11         hexStr.at(i) =  Value + '0';
12     }
13 
14     hexStr = hexStr.substr(0, i);
15 
16     reverse(hexStr.begin(), hexStr.end());
17 
18     if (hexStr.length() < 6)
19     {
20         string add( 6 - hexStr.length(), '0');
21         hexStr = add + hexStr;
22     }
23 
24     return hexStr;
25 }

 1 int main()
 2 {
 3 
 4     string input0;                                                          //存放输入的字符
 5     string input1;                                                          //存放二进制序列
 6     string deciToBin_8bit(int);                                    //十进制到二进制函数原型
 7     string base64_encryption(const string);                                //加密函数原型
 8     string base64_decryption(const string);
 9     cout << "Input:" << endl;
10     cin >> input0;                                    //输入的ASCII码字符串
11     cout << endl;
12 
13     for ( auto &x : input0)
14         input1 += deciToBin_8bit(static_cast<int>(x));                       //得到二进制序列
15 
16     string out0 = base64_encryption(input1);
17 
18     cout << out0 << endl;
19 
20     cout<<endl;
21 
22     string out1 = base64_decryption(out0);
23 
24     cout << out1 << endl;
25 
26     return 0;
27 }

1 #include <iostream>
2 #include <cstdlib>
3 #include <cmath>
4 #include <algorithm>
5 #include <cctype>