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凯撒加密算法C语言实现

凯撒加密算法C语言实现
#include<stdio.h>
#include<conio.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)&);
}
while(ch>='a'&&ch<='z')
{
return ('a' (ch-'a' n)&);
}
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 logo()/*显示版权信息*/ {
printf("\nctu_85 Encryption [Version:1.0.0]");
printf("\nCopyright (C) ctu_85.\n");
return;
}


main()
{
int i,n;
char ch0,ch1;
FILE *in,*out;
char infile[20],outfile[20];

textbackground(BLACK);
textcolor(LIGHTGREEN);
clrscr();

logo();
sleep(3);/*等待3秒*/
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();
exit(0);
}

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();
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"))==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();
logo();
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();
logo();
printf("\nGood Bye!\n");
sleep(3);
}