凯撒密码（Caesar）的原理和算法实现
1.凯撒密码的原理：
它是一种古典密码体质下的一种密码，是一种移位密码，具有单表密码的性质，密文和明文都使用同一个映射，为了保证加密的可逆性，要求映射都是一一对应。
2.凯撒密码的公式：
加密公式： f(a)=(a+N) mod 26
解密公式： f(a)=(a+(26-N)) mod 26
其中N代表的是位移数，也可以算是k；
3.代码实现：
//// Created by tangleia on /2/21.//#include<stdlib.h>#include<string.h>#include<stdio.h>//加密int kaisa_encrypt(char *text,char *result,int k){char small_letter[26]={'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'};char big_letter[26]={'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'};//判断是否符合if(text == NULL || k <= 0){return -1;}int m = strlen(text); //获取明文的长度if(m <= 0){return -1;}for(int i=0;i<m;i++) {if (text[i] >= 'A' && text[i] <= 'Z') {result[i] = big_letter[((text[i] - 'A') + k) % 26];} else if (text[i] >= 'a' && text[i] <= 'z') {result[i] = small_letter[((text[i] - 'a') + k) % 26];} else result[i] = text[i];}return 0;}//解密int kaisa_decrypt(char *text,char *result,int k){int p;char small_letter[26]={'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'};char big_letter[26]={'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'};if(text == NULL || k <= 0){return -1;}int m = strlen(text);if(m <= 0){return -1;}for(int i=0;i<m;i++) {if (text[i] >= 'A' && text[i] <= 'Z') {p = ((text[i] - 'A') - k);while (p < 0)p += 26;result[i] = big_letter[p];} else if (text[i] >= 'a' && text[i] <= 'z') {p = ((text[i] - 'a') - k);while (p < 0)p += 26;result[i] = small_letter[p];}else result[i] = text[i];}return 0;}int main(){char text[50]="";char result[50]="";int k;int type;/**欢迎**/printf("--------欢迎使用凯撒密码-----------\n");printf("请填写明文或者密文\n");scanf("%[^\n]",text);printf("请选择加密方式，输入1加密，输入2解密\n");scanf("%d",&type);printf("请输入密钥k\n");scanf("%d",&k);if(type == 1){/***加密****/kaisa_encrypt(text,result,k);printf("明文%s的密文为:%s\n",text,result);}else if(type == 2){/***解密****/kaisa_decrypt(text,result,k);printf("密文%s的明文为:%s\n",text,result);}return 0;}
用了c语言实现的加密解密的算法
验证
加密验证
解密验证
