#include #include #include #include #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(); }

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