Encrypt and decrypt {substitution cipher}
Encrypt and decrypt a plain text using substitution cipher(normal method)
In cryptography, a Caesar cipher, also known as a Caesar's
cipher, the shift cipher, Caesar's code or Caesar shift,
is one of the simplest and most widely known encryption
techniques. It is a type of substitution cipher in which each letter in the
plaintext
is replaced by a letter some fixed number of positions down the alphabet. For
example, with a shift of 3, A
would be replaced by D, B
would become E, and so on. The
method is named after Julius Caesar, who used it to communicate with his generals.Later
this method was advanced with the key being taken greater than 3 and this
method is called normal substitution method.
METHOD OF ENCRYPTION-: The method of encyrption is
exactly the same way as we have done in experiment no:1, but the only
difference is that the key is user input (instead of 3). According to the key
the cipher is formed and then decrypted at the receiver end.
PROGRAM in C++-:
#include<stdio.h>
#include<string.h>
#include<conio.h>
#include<process.h>
void main()
{
int ch=1,n=0,key;
char str[20];
clrscr();
printf("enter key to be
used\n");
scanf("%d",&key);
key=key%26;
do
{
printf("enter 1 for
encryption\n");
printf("enter 2 for
decryption\n");
printf("enter 0 for
exit\n");
scanf("%d",&ch);
if(ch==1)
{
n=0;
printf("enter text to
be encrypted");
fflush(stdin);
scanf("%s",&str);
while(str[n]!='\0')
{
if(str[n]>=65&&str[n]<=90)
{
if((str[n]+32+key)>122)
{
str[n]=str[n]+32+key-122+96;
}
else
{
str[n]=str[n]+32+key;
}
n++;
}
puts(str);
}
if(ch==2)
{
n=0;
printf("enter text to
be decrypted"); }
fflush(stdin);
scanf("%s",&str);
while(str[n]!='\0')
{
if(str[n]>=97&&str[n]<=122)
{
if((str[n]-(32+key))<65)
{
str[n]=str[n]-(32+key)+26;
}
else
{
str[n]=str[n]-(32+key);
}
}
n++;
}
puts(str);
}
}
while(ch!=0);
getch();
}
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