AIM :
To implement the simple substitution technique named Caesar cipher using C language.
ALGORITHM :
Step 1 :
Read the plain text from the user.
Step 2 : Read the key value from the user
Step 3 :
If the key is positive then encrypt the text by adding the key with each character in the plain text
Step 4 :
Else subtract the key from the plain text.
Step 5 :
Display the cipher text obtained above.
PROGRAM :
#include<stdio.h>
#include <string.h>
#include<conio.h>
#include <ctype.h>
int main()
{
char plain[10], cipher[10];
int key,i,length;
int result;
printf("\n Enter the plain text:");
scanf("%s", plain);
printf("\n Enter the key value:");
scanf("%d", &key);
printf("\n \n \t PLAIN TEXt: %s",plain);
printf("\n \n \t ENCRYPTED TEXT: ");
for(i = 0, length = strlen(plain); i < length; i++)
{
cipher[i]=plain[i] + key;
if (isupper(plain[i]) && (cipher[i] > 'Z'))
cipher[i] = cipher[i] - 26;
if (islower(plain[i]) && (cipher[i] > 'z'))
cipher[i] = cipher[i] - 26;
printf("%c", cipher[i]);
}
printf("\n \n \t AFTER DECRYPTION : ");
for(i=0;i<length;i++)
{
plain[i]=cipher[i]-key;
if(isupper(cipher[i])&&(plain[i]<'A'))
plain[i]=plain[i]+26;
if(islower(cipher[i])&&(plain[i]<'a'))
plain[i]=plain[i]+26;
printf("%c",plain[i]);
}
return 0;
}
OUTPUT :
RESULT :
Thus the implementation of Caesar cipher had been executed successfully
AIM :
To write a C program to implement the Playfair Substitution technique.
ALGORITHM :
Step 1 :
Read the plain text from the user
Step 2 :
Read the keyword from the user
Step 3 :
Arrange the keyword without duplicates in a 5*5 matrix in the row
order and fill the remaining cells with missed out letters in
alphabetical order. Note that ‘i’ and ‘j’ takes the same cell.
Step 4 :
Group the plain text in pairs and match the corresponding corner
letters by forming a rectangular grid.
step 5 :
Display the obtained cipher text
PROGRAM :
#include<stdio.h>
#include<conio.h>
#include<string.h>
#include<ctype.h>
#define MX 5
void playfair(char ch1,char ch2, char key[MX][MX])
{
int i,j,w,x,y,z;
FILE *out;
if((out=fopen("cipher.txt","a+"))==NULL)
{
printf("File Corrupted.");
}
for(i=0;i<MX;i++)
{
for(j=0;j<MX;j++)
{
if(ch1==key[i][j])
{
w=i;
x=j;
}
else if(ch2==key[i][j])
{
y=i;
z=j;
}}}
//printf("%d%d %d%d",w,x,y,z);
if(w==y)
{
x=(x+1)%5;z=(z+1)%5;
printf("%c%c",key[w][x],key[y][z]);
fprintf(out, "%c%c",key[w][x],key[y][z]);
}
else if(x==z)
{
w=(w+1)%5;y=(y+1)%5;
printf("%c%c",key[w][x],key[y][z]);
fprintf(out, "%c%c",key[w][x],key[y][z]);
}
else
{
printf("%c%c",key[w][z],key[y][x]);
fprintf(out, "%c%c",key[w][z],key[y][x]);
}
fclose(out);
}
int main()
{
int i,j,k=0,l,m=0,n;
char key[MX][MX],keyminus[25],keystr[10],str[25]={0};
char
alpa[26]={'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'};
printf("\nEnter key:");
gets(keystr);
printf("\nEnter the plain text:");
gets(str);
n=strlen(keystr);
//convert the characters to uppertext
for (i=0; i<n; i++)
{
if(keystr[i]=='j')keystr[i]='i';
else if(keystr[i]=='J')keystr[i]='I';
keystr[i] = toupper(keystr[i]);
}
//convert all the characters of plaintext to uppertext
for (i=0; i<strlen(str); i++)
{
if(str[i]=='j')str[i]='i';
else if(str[i]=='J')str[i]='I';
str[i] = toupper(str[i]);
}
j=0;
for(i=0;i<26;i++)
{
for(k=0;k<n;k++)
{
if(keystr[k]==alpa[i])
break;
else if(alpa[i]=='J')
break;
}
if(k==n)
{
keyminus[j]=alpa[i];j++;
}
}
//construct key keymatrix
k=0;
for(i=0;i<MX;i++)
{
for(j=0;j<MX;j++)
{
if(k<n)
{
key[i][j]=keystr[k];
k++;}
else
{
key[i][j]=keyminus[m];m++;
}
printf("%c ",key[i][j]);
}
printf("\n");
}
printf("\n\nEntered text :%s\nCipher Text :",str);
for(i=0;i<strlen(str);i++)
{
if(str[i]=='J')str[i]='I';
if(str[i+1]=='\0')
playfair(str[i],'X',key);
else
{
if(str[i+1]=='J')str[i+1]='I';
if(str[i]==str[i+1])
playfair(str[i],'X',key);
else
{
playfair(str[i],str[i+1],key);
i++;
}}
}
return 0;
}
OUTPUT :
RESULT : Thus the Playfair cipher substitution technique had been implemented successfully.
AIM :
To write a C program to implement the hill cipher substitution techniques.
ALGORITHM :
Step 1 :
Read the plain text and key from the user.
Step 2 :
Split the plain text into groups of length three
Step 3 :
Arrange the keyword in a 3*3 matrix.
Step 4 :
Multiply the two matrices to obtain the cipher text of length three.
Step 5 :
Combine all these groups to get the complete cipher text.
PROGRAM :
#include<stdio.h>
#include<conio.h>
#include<string.h>
int main(){
unsigned int a[3][3]={{6,24,1},{13,16,10},{20,17,15}};
unsigned int b[3][3]={{8,5,10},{21,8,21},{21,12,8}};
int i,j, t=0;
unsigned int c[20],d[20];
char msg[20];
printf("Enter plain text: ");
scanf("%s",msg);
for(i=0;i<strlen(msg);i++)
{
c[i]=msg[i]-65;
unsigned int a[3][3]={{6,24,1},{13,16,10},{20,17,15}};
unsigned int b[3][3]={{8,5,10},{21,8,21},{21,12,8}};
printf("%d ",c[i]);
}
for(i=0;i<3;i++)
{ t=0;
for(j=0;j<3;j++)
{
t=t+(a[i][j]*c[j]);
}
d[i]=t%26;
}
printf("\nEncrypted Cipher Text :");
for(i=0;i<3;i++)
printf(" %c",d[i]+65);
for(i=0;i<3;i++)
{
t=0;
for(j=0;j<3;j++)
{
t=t+(b[i][j]*d[j]);
}
c[i]=t%26;
}
printf("\nDecrypted Cipher Text :");
for(i=0;i<3;i++)
printf(" %c",c[i]+65);
getch();
return 0;
}
OUTPUT :
RESULT :
Thus the hill cipher substitution technique had been implemented successfully
AIM :
To implement the Vigenere Cipher substitution technique using C program
ALGORITHM :
Step 1 :
Arrange the alphabets in row and column of a 26*26 matrix
Step 2 :
Circulate the alphabets in each row to position left such that the first letter
is attached to last.
Step 3 :
Repeat this process for all 26 rows and construct the final key matrix.
Step 4 :
The keyword and the plain text is read from the user.
Step 5 :
The characters in the keyword are repeated sequentially so as to
match with that of the plain text.
Step 6 :
Pick the first letter of the plain text and that of the keyword as the row
indices and column indices respectively.
Step 7 :
The junction character where these two meet forms the cipher character
Step 8 :
Repeat the above steps to generate the entire cipher text.
PROGRAM :
#include <stdio.h>
#include<conio.h>
#include <ctype.h>
#include <string.h>
void encipher();
void decipher();
int main()
{
int choice;
while(1)
{
printf("\n1. Encrypt Text");
printf("\n2. Decrypt Text");
printf("\n3. Exit");
printf("\n\nEnter Your Choice : ");
scanf("%d",&choice);
if(choice == 3)
exit(0);
else if(choice == 1)
encipher();
else if(choice == 2)
decipher();
else
printf("Please Enter Valid Option.");
}
}
void encipher()
{
unsigned int i,j;
char input[50],key[10];
printf("\n\nEnter Plain Text: ");
scanf("%s",input);
printf("\nEnter Key Value: ");
scanf("%s",key);
printf("\nResultant Cipher Text: ");
for(i=0,j=0;i<strlen(input);i++,j++)
{
if(j>=strlen(key))
{ j=0;
}
printf("%c",65+(((toupper(input[i])-65)+(toupper(key[j])-
65))%26));
}}
void decipher()
{
unsigned int i,j;
char input[50],key[10];
int value;
printf("\n\nEnter Cipher Text: ");
scanf("%s",input);
printf("\n\nEnter the key value: ");
scanf("%s",key);
for(i=0,j=0;i<strlen(input);i++,j++)
{
if(j>=strlen(key))
{ j=0; }
value = (toupper(input[i])-64)-(toupper(key[j])-64);
if( value < 0)
{ value = value * -1;
}
printf("%c",65 + (value % 26));
}
return 0;
}
OUTPUT :
RESULT :
Thus , The program is executed perfectly and output is verified.
AIM :
To write a C program to implement the rail fence transposition technique.
ALGORRITHM :
Step 1 :
Read the Plain text.
Step 2 :
Arrange the plain text in row columnar matrix format
Step 3 :
Now read the keyword depending on the number of columns of the plain text
Step 4 :
Arrange the characters of the keyword in sorted order and the
corresponding columns of the plain text.
Step 5 :
Read the characters row wise or column wise in the former order to get the
cipher text.
PROGRAM :
#include<stdio.h>
#include<conio.h>
#include<string.h>
int main()
{
int i,j,k,l;
char a[20],c[20],d[20];
printf("\n\t\t RAIL FENCE TECHNIQUE");
printf("\n\nEnter the input string : ");
gets(a);
l=strlen(a);
/Ciphering/
for(i=0,j=0;i<l;i++)
{
if(i%2==0)
c[j++]=a[i];
}
for(i=0;i<l;i++)
{
if(i%2==1)
c[j++]=a[i];
}
c[j]='\0';
printf("\nCipher text after applying rail fence :");
printf("\n%s",c);
/Deciphering/
if(l%2==0)
k=l/2;
else
k=(l/2)+1;
for(i=0,j=0;i<k;i++)
{
d[j]=c[i];
j=j+2;
}
for(i=k,j=1;i<l;i++)
{
d[j]=c[i];
j=j+2;
}
d[l]='\0';
printf("\nText after decryption : ");
printf("%s",d);
return 0;
}
OUTPUT :
RESULT :
Thus the rail fence algorithm had been executed successfully
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