实训一古典加密算法一、实训目的熟悉古典数据加密的工作原理，并且能够利用相关加密算法进行加解密。

二、实训环境一台安装有Windows XP的计算机。

三、实训内容用C编写程序实现对某一文件内容用恺撒加密法进行加密，然后用解密程序进行解密。

四、实训步骤1、用C编写程序实现对某一文件内容用恺撒加密法进行加密。

2、用解密程序对密文进行解密。

五、实训效果检测上交加密程序、解密程序、原文（.txt文档）解:（1）使用的加密、解密程序代码如下：#include<stdio.h>#include<conio.h>#include<string.h>#include<malloc.h>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'){return ('A'+(ch-'A'+n)%26);}while(ch>='a'&&ch<='z'){return ('a'+(ch-'a'+n)%26);}return ch;}void menu()/*菜单，1.加密，2.解密，3.暴力破解，密码只能是数字*/{//clrscr();printf("\n========================================================="); printf("\n1.Encrypt the file");printf("\n2.Decrypt the file");printf("\n3.Force decrypt file");printf("\n4.Quit\n");printf("=========================================================\n"); printf("Please select a item:");return;}void main(){int i,n;char ch0,ch1;FILE *in,*out;char infile[20],outfile[20];//textbackground(BLACK);//textcolor(LIGHTGREEN);//clrscr();menu();ch0=getch();while(ch0!='4'){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();}printf("Please input 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);getch();}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"))==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);/*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);}if(ch0=='3'){// clrscr();printf("\nPlease input the infile:");scanf("%s",infile);/*输入需要解密的文件名*/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 input the outfile:");scanf("%s",outfile);/*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);}for(i=1;i<=25;i++)/*暴力破解过程，在察看信息正确后，可以按'Q'或者'q'退出*/ {rewind(in);rewind(out);// clrscr();printf("==========================================================\n"); printf("The outfile is:\n");printf("==========================================================\n"); while(!feof(in)){ch1=encrypt(fgetc(in),26-i);putch(ch1);fputc(ch1,out);}printf("\n========================================================\n");printf("The current key is: %d \n",i);/*显示当前破解所用密码*/printf("Press 'Q' to quit and other key to continue......\n");printf("==========================================================\n");ch1=getch();if(ch1=='q'||ch1=='Q')/*按'Q'或者'q'时退出*/{// clrscr();printf("\nGood Bye!\n");fclose(in);fclose(out);// sleep(3);// exit(0);}}printf("\nForce decrypt is over!\n");fclose(in);fclose(out);// sleep(1);}menu();ch0=getch();}//clrscr();printf("\nGood Bye!\n");（2）原文文件为whx.txt，其内容：ahhdhjshjdhjsdhj。