实验要求：
实现维吉尼亚密码，用键盘接收明文和密钥，屏幕打印密文和解密后的明文。大小写铭感，明文小写则密文大写，明文大写则密文小写。
维吉尼亚替换表.jpg
实际问题：
接收密文的字符串少申请了一位空间，导致空间控制的一个bug，花了一个小时才定位到问题，之前完全没有想到是这个问题。大概就是因为少了一位空间，导致\0被覆盖，然后编译器帮我扩展了五个字节，导致这五个字没有初始化，所以输出密文的时候后面总是有莫名其妙的字符出现。
核心代码实现：
ciphertext= (char*)calloc(plainlen+1, sizeof(char));
...
for (int j = 0 ; j < plainlen ; j++) //加密过程
{
if (plaintext[j] >= 65 && plaintext[j] <= 90)
ciphertext[j] = ((plaintext[j] - 65) + (key[j] - 65) % 26 + 97);
else if(plaintext[j] >= 97 && plaintext[j] <= 122)
ciphertext[j] = ((plaintext[j] - 97) + (key[j] - 65) % 26 + 65);
else
ciphertext[j] = plaintext[j];
}
源码：
// 维吉尼亚密码加密-键盘接收加密解密
//**2015-9-24**
#include "stdafx.h"
#include <iostream>
using namespace std;
int array_num = 500;
void encipher(char [], char [], char []);
void decipher(char [], char [], char []);
int main()
{
int plainlen,TEMP; //申请原文，密文，密钥的空间并初始化
char *plaintext,*key,*ciphertext;
plaintext = (char*)calloc(array_num, sizeof(char));
key = (char*)calloc(array_num, sizeof(char));
cout << "输入密文" << endl;
cin.getline(plaintext, array_num);
cout << "输入key" << endl;
cin.getline(key, array_num);
plainlen = strlen(plaintext);
ciphertext= (char*)calloc(plainlen+1, sizeof(char)); //密文的空间由输入明文的长度确定
encipher(plaintext, key, ciphertext);//加密
int cipherlen = strlen(ciphertext);
decipher(ciphertext, key, plaintext);//解密
system("pause");
return 0;
}
void encipher(char plaintext[], char key[], char ciphertext[])
{
cout << "-------------------加密过程-------------------" << endl;
cout <<"***原文***\n"<< plaintext << endl << endl;
char temp;
int keylen = strlen(key);
int plainlen = strlen(plaintext);
for (int i = 0; i < plainlen; i++) //处理密钥字符串全部为大写，长度和明文以及密文长度相同
{
if (key[i] >= 97 && (key[i] <= 122))
{
temp = key[i%keylen] - 32;
key[i] = temp;
}
else
key[i] = key[i%keylen];
}
for (int j = 0 ; j < plainlen ; j++) //加密过程
{
if (plaintext[j] >= 65 && plaintext[j] <= 90)
ciphertext[j] = (((plaintext[j] - 65) + (key[j] - 65)) % 26 + 97);
else if(plaintext[j] >= 97 && plaintext[j] <= 122)
ciphertext[j] = (((plaintext[j] - 97) + (key[j] - 65)) % 26 + 65);
else
ciphertext[j] = plaintext[j];
}
cout <<"***密文***\n"<< ciphertext << endl;
}
void decipher(char ciphertext[], char key[], char plaintext[])
{
cout << "-----------------解密过程--------------------"<<endl;
cout << "***密文***\n" << ciphertext << endl << endl;
//cout << "***key***\n" << key << endl << endl;
int cipherlen = strlen(ciphertext);
for (int j = 0; j < cipherlen; j++) //解密过程
{
if (ciphertext[j] >= 65 && ciphertext[j] <= 90)
plaintext[j] = (((ciphertext[j] - 65+26) - (key[j] - 65))%26 + 97);
else if (ciphertext[j] >= 97 && ciphertext[j] <= 122)
plaintext[j] = (((ciphertext[j] - 97+26) - (key[j] - 65))%26 + 65);
else
plaintext[j] = ciphertext[j];
}
cout << "***原文***\n" << plaintext << endl;
}