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Experiment No 2: Name: Pallavi Bharti Roll No: 18141112

Pallavi Bharti implemented the Playfair cipher encryption model in C programming language. The program takes a key and plaintext as input, constructs a 5x5 key matrix based on the key, and uses the Playfair cipher rules to encrypt pairs of letters into ciphertext by their positions in the matrix. The program outputs the key matrix, encrypts the given plaintext into ciphertext, and concludes that it has successfully studied and implemented the Playfair cipher encryption technique.

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Pallavi Bharti
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44 views4 pages

Experiment No 2: Name: Pallavi Bharti Roll No: 18141112

Pallavi Bharti implemented the Playfair cipher encryption model in C programming language. The program takes a key and plaintext as input, constructs a 5x5 key matrix based on the key, and uses the Playfair cipher rules to encrypt pairs of letters into ciphertext by their positions in the matrix. The program outputs the key matrix, encrypts the given plaintext into ciphertext, and concludes that it has successfully studied and implemented the Playfair cipher encryption technique.

Uploaded by

Pallavi Bharti
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Name: Pallavi Bharti

Roll No: 18141112

Experiment No 2
Title: Implement Playfair cipher model using any programming language

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 Currupted.");
}
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);
}
void 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]);
}
// store all characters except key
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");
}
// construct diagram and convert to cipher text
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++;
}
}
}
getch();
}
Output:

Conclusion: Thus, I have studied and implement playfair cipher.

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