凯撒密码--C语言实现(共8页)

1、精选优质文档-倾情为你奉上凯撒密码是一种非常古老的加密方法，相传当年凯撒大地行军打仗时为了保证自己的命令不被敌军知道，就使用这种特殊的方法进行通信，以确保信息传递的安全。他的原理很简单，说到底就是字母于字母之间的替换。下面让我们看一个简单的例子：“baidu”用凯撒密码法加密后字符串变为“edlgx”，它的原理是什么呢？把“baidu”中的每一个字母按字母表顺序向后移3位，所得的结果就是刚才我们所看到的密文。/*凯撒密码实现 要求，将明文字母变成它后面第三个字母，后面的循环到前面！ 公式为f(a)=(f(a)+3)%26*/#include <stdio.h>int main()

2、char P100;/*定义明文长度*/ char C100;/*定义密文长度*/ int K=3,i; printf("Please input Plaintext:n"); /*输入明文*/ gets(P); /* 接受明文*/ for(i=0;Pi!='0'i+) /*逐个判断字母的大小*/ if(Pi>='a'&&Pi<='z') /*小写字母 */ Ci=(Pi-'a'+K)%26+'a' else if(Pi>='A'&&am

3、p;Pi<='Z')/*大写字母 */ Ci=(Pi-'A'+K)%26+'A' else Ci=' '/*如果不是字母，转换为空格*/ printf("The Ciphertext is :n%sn",C);/*输出密文*/ getch(); return 0; 1、程序结构化，用函数分别实现2、对文件的加密，解密输出到文件#include<stdio.h>#include<conio.h>void menu()/*菜单，1.加密 2.解密 3.退出*/clrscr();prin

4、tf("n=");printf("n1.Encrypt the file");printf("n2.Decrypt the file");printf("n3.Quitn");printf("=n");printf("Please select a item:");return;char encrypt(char ch,int n)/*加密函数，把字符向右循环移位n*/while(ch>='A'&&ch<='Z')r

5、eturn ('A'+(ch-'A'+n)%26);while(ch>='a'&&ch<='z')return ('a'+(ch-'a'+n)%26);return ch;main()int i,n;char ch0,ch1;FILE *in,*out;char infile10,outfile10;textbackground(RED);textcolor(LIGHTGREEN);clrscr();menu();ch0=getch();while(ch0!='3

6、')if(ch0='1') clrscr(); printf("nPlease input the infile:"); scanf("%s",infile);/*输入需要加密的文件名*/ if(in=fopen(infile,"r")=NULL) printf("Can not open the infile!n"); printf("Press any key to exit!n"); getch(); exit(0); printf("Please inp

7、ut the key:"); scanf("%d",&n);/*输入加密密码*/ printf("Please input the outfile:"); scanf("%s",outfile);/*输入加密后文件的文件名*/ if(out=fopen(outfile,"w")=NULL) printf("Can not open the outfile!n"); printf("Press any key to exit!n"); fclose(in);

8、getch(); exit(0); while(!feof(in)/*加密*/ fputc(encrypt(fgetc(in),n),out); printf("nEncrypt is over!n"); fclose(in); fclose(out); sleep(1);if(ch0='2') clrscr(); printf("nPlease input the infile:"); scanf("%s",infile);/*输入需要解密的文件名*/ if(in=fopen(infile,"r"

9、)=NULL) printf("Can not open the infile!n"); printf("Press any key to exit!n"); getch(); exit(0); printf("Please input the key:"); scanf("%d",&n);/*输入解密密码（可以为加密时候的密码）*/ n=26-n; printf("Please input the outfile:"); scanf("%s",outfile);/*

10、输入解密后文件的文件名*/ if(out=fopen(outfile,"w")=NULL) printf("Can not open the outfile!n"); printf("Press any key to exit!n"); fclose(in); getch(); exit(0); while(!feof(in) fputc(encrypt(fgetc(in),n),out); printf("nDecrypt is over!n"); fclose(in); fclose(out); sleep(1

11、);clrscr(); printf("nGood Bye!n");sleep(3); getch();-/*移位法:*/#include <stdio.h>#include <stdlib.h>char *Encrypt(char *pwd,int key) /*加密*/for(int i=0;*(pwd+i)!='0'i+)if(*(pwd+i)>='a'&&*(pwd+i)<='z')*(pwd+i)=(*(pwd+i)-'a'+key)%26+'

12、;a'else if(*(pwd+i)>='A'&&*(pwd+i)<='Z')*(pwd+i)=(*(pwd+i)-'A'+key)%26+'A'return pwd;char *Decrypt(char *pwd,int key) /*解密*/for(int i=0;*(pwd+i)!='0'i+)if(*(pwd+i)>='a'&&*(pwd+i)<='z')if(*(pwd+i)-'a'>=

13、key%26)*(pwd+i)=*(pwd+i)-key%26;else *(pwd+i)='z'-(key%26-(*(pwd+i)-'a')-1;else if(*(pwd+i)>='A'&&*(pwd+i)<='Z')if(*(pwd+i)-'A'>=key%26)*(pwd+i)=*(pwd+i)-key%26;else *(pwd+i)='Z'-(key%26-(*(pwd+i)-'A')-1;return pwd;void main()c

14、har *pwd;int key;pwd=(char*)malloc(sizeof(char);printf("Input your password:");gets(pwd);printf("Input a key:");scanf("%d",&key);printf("The Ciphertext is:");printf("%sn",Encrypt(pwd,key);-/*替换法：*/#include <stdio.h>#include <stdlib.h>

15、#include <string.h>void table(char *keyword) /*筛选密钥(去重复去空格)*/int i,j,k;for(i=0;*(keyword+i)!='0'i+)for(j=i;*(keyword+j)!='0'j+)if(i!=j)if(*(keyword+i)=*(keyword+j)|*(keyword+j)=' ')for(k=j;*(keyword+k)!='0'k+)*(keyword+k)=*(keyword+k+1);j-;void newTab(char *keyw

16、ord) /*生成密钥表*/char ch;int i;int t;for(t=0;*(keyword+t)!='0't+);for(ch='a'ch<='z'ch+)for(i=0;*(keyword+i)!=ch;i+)if(*(keyword+i)='0')*(keyword+t)=ch;t+;break;*(keyword+t)='0'char *Ciphertext(char *keyword,char *Plaintext) /*按密码表加密*/char ch;int i,j;for(i=0;*(

17、Plaintext+i)!='0'i+)for(ch='a',j=0;ch<='z'ch+,j+)if(*(Plaintext+i)=ch)*(Plaintext+i)=*(keyword+j);break;return Plaintext;char *Decrypt(char *keyword,char *Plaintext) /*解密*/char ch;int i,j;for(i=0;*(Plaintext+i)!='0'i+)for(ch='a',j=0;*(keyword+j)!='0'ch+,j+)if(*(Plaintext+i)=*(keyword+j)*(Plaintext+i)=ch;break;return Plaintext;void main()char *keyword,*Plaintext,*tmp=NULL;keyword=(char*)malloc(sizeof(char);Plaintext=(char*)malloc(sizeof(char);printf(&quo