凯撒密码的解密程序c语言是什么（凯撒密码c++代码）
凯撒密码的解密程序c语言是什么（凯撒密码c++代码）
凯撒密码就是简单的加上一个数，'a'+3='d';'z'+3='c' 假设原文全是小写字母，那么 char plain[N]={...}; //明文 char cipher[N]={};//密文 int key=3; int i=0,temp; for(i=0;iN;i++) {if(plain[i]!=' ') {temp=plain[i]+key-'a'; temp=temp%26; cipher[i]=temp+'a'; } else cipher[i]=plain[i]; } 这样就完成了加密，密文数组里面就是对原文加密后的密文，key是密钥。
#includestdio.h
#includestring.h
void main ()
{
char str[100];
char str1[100];
printf("输入字符串:");
scanf("%s",str);
int len;
len=strlen(str);
for(int i=0;i＜len;i++)
{
str1[i]=(str[i]-97+3)%26+97;
}
str1[len]='\0';
printf ("密文为:%s\n",str1);
}
（2）kaiser加密算法
具体程序：
#includestdio.h
#includeconio.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;
}
main()
{
int i,n;
char ch0,ch1;
FILE *in,*out;
char infile[20],outfile[20];
textbackground(BLACK);
textcolor(LIGHTGREEN);
clrscr();
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();
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");
sleep(3);
}
.
希望能够帮助你 ^_^ 也希望能够选为最佳答案！
