C Program to Perform Cryptography using Transposition Technique

This is a C Program to implement transposition technique. A transposition cipher is a method of encryption, where the positions held by plaintext characters or group of characters are shifted as per a system, such that ciphertext is a permutation of the plaintext. That means only the order of the character or group of characters is changed.

Here is source code of the C Program to Perform Cryptography Using Transposition Technique. The C program is successfully compiled and run on a Linux system. The program output is also shown below.

```
#include<stdio.h>
```
```
#include<string.h>
```
```
 
```
```
void cipher(int i, int c);
```
```
int findMin();
```
```
void makeArray(int, int);
```
```
 
```

char arr[22][22], darr[22][22], emessage[111], retmessage[111], key[55];

```
char temp[55], temp2[55];
```
```
int k = 0;
```
```
 
```
```
int main() {
```
```
    char *message, *dmessage;
```
```
 
```
```
    int i, j, klen, emlen, flag = 0;
```
```
    int r, c, index, min, rows;
```
```
 
```
```
    printf("Enetr the key\n");
```
```
    fflush(stdin);
```
```
    gets(key);
```
```
 
```

    printf("\nEnter message to be ciphered\n");

```
    fflush(stdin);
```
```
    gets(message);
```
```
 
```
```
    strcpy(temp, key);
```
```
    klen = strlen(key);
```
```
 
```
```
    k = 0;
```
```
    for (i = 0;; i++) {
```
```
        if (flag == 1)
```
```
            break;
```
```
 
```

        for (j = 0; key[j] != NULL; j++) {

```
            if (message[k] == NULL) {
```
```
                flag = 1;
```
```
                arr[i][j] = '-';
```
```
            } else {
```

                arr[i][j] = message[k++];

```
            }
```
```
        }
```
```
    }
```
```
    r = i;
```
```
    c = j;
```
```
 
```
```
    for (i = 0; i < r; i++) {
```
```
        for (j = 0; j < c; j++) {
```
```
            printf("%c ", arr[i][j]);
```
```
        }
```
```
        printf("\n");
```
```
    }
```
```
 
```
```
    k = 0;
```
```
 
```
```
    for (i = 0; i < klen; i++) {
```
```
        index = findMin();
```
```
        cipher(index, r);
```
```
    }
```
```
 
```
```
    emessage[k] = '\0';
```
```
    printf("\nEncrypted message is\n");
```

    for (i = 0; emessage[i] != NULL; i++)

```
        printf("%c", emessage[i]);
```
```
 
```
```
    printf("\n\n");
```
```
    //deciphering
```
```
 
```
```
    emlen = strlen(emessage);
```

    //emlen is length of encrypted message

```
 
```
```
    strcpy(temp, key);
```
```
 
```
```
    rows = emlen / klen;
```

    //rows is no of row of the array to made from ciphered message

```
    rows;
```
```
    j = 0;
```
```
 
```

    for (i = 0, k = 1; emessage[i] != NULL; i++, k++) {

```
        //printf("\nEmlen=%d",emlen);
```
```
        temp2[j++] = emessage[i];
```
```
        if ((k % rows) == 0) {
```
```
            temp2[j] = '\0';
```
```
            index = findMin();
```
```
            makeArray(index, rows);
```
```
            j = 0;
```
```
        }
```
```
    }
```
```
 
```
```
    printf("\nArray Retrieved is\n");
```
```
 
```
```
    k = 0;
```
```
    for (i = 0; i < r; i++) {
```
```
        for (j = 0; j < c; j++) {
```
```
            printf("%c ", darr[i][j]);
```
```
            //retrieving message
```

            retmessage[k++] = darr[i][j];

```
 
```
```
        }
```
```
        printf("\n");
```
```
    }
```
```
    retmessage[k] = '\0';
```
```
 
```
```
    printf("\nMessage retrieved is\n");
```
```
 
```

    for (i = 0; retmessage[i] != NULL; i++)

```
        printf("%c", retmessage[i]);
```
```
 
```
```
    getch();
```
```
    return (0);
```
```
}
```
```
 
```
```
void cipher(int i, int r) {
```
```
    int j;
```
```
    for (j = 0; j < r; j++) {
```
```
        {
```
```
            emessage[k++] = arr[j][i];
```
```
        }
```
```
    }
```
```
    // emessage[k]='\0';
```
```
}
```
```
 
```
```
void makeArray(int col, int row) {
```
```
    int i, j;
```
```
 
```
```
    for (i = 0; i < row; i++) {
```
```
        darr[i][col] = temp2[i];
```
```
    }
```
```
}
```
```
 
```
```
int findMin() {
```
```
    int i, j, min, index;
```
```
 
```
```
    min = temp[0];
```
```
    index = 0;
```
```
    for (j = 0; temp[j] != NULL; j++) {
```
```
        if (temp[j] < min) {
```
```
            min = temp[j];
```
```
            index = j;
```
```
        }
```
```
    }
```
```
 
```
```
    temp[index] = 123;
```
```
    return (index);
```
```
}
```

Output:

$ gcc TranspositionTechnique.c
$ ./a.out
 
Enter the key
hello
 
Enter the message to be ciphered
how are you
 
h o w   a
r e   y o
u - - - -
 
Encrypted message is
oe-hruw - y-ao-
 
Array Retrieved is
h o w   a
r e   y o
u - - - -
 
Message retrieved is
how are you----

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