Hill Cipher C Program Code Example

Example: hill cipher encryption in c

#include<stdio.h> #include<math.h>   float encrypt[3][1], decrypt[3][1], a[3][3], b[3][3], mes[3][1], c[3][3];   void encryption();	//encrypts the message void decryption();	//decrypts the message void getKeyMessage();	//gets key and message from user void inverse();		//finds inverse of key matrix   void main() { 	getKeyMessage(); 	encryption(); 	decryption(); }   void encryption() { 	int i, j, k; 	 	for(i = 0; i < 3; i++) 		for(j = 0; j < 1; j++) 			for(k = 0; k < 3; k++) 				encrypt[i][j] = encrypt[i][j] + a[i][k] * mes[k][j]; 	 	printf("\nEncrypted string is: "); 	for(i = 0; i < 3; i++) 		printf("%c", (char)(fmod(encrypt[i][0], 26) + 97));   }   void decryption() { 	int i, j, k; 	 	inverse(); 	 	for(i = 0; i < 3; i++) 		for(j = 0; j < 1; j++) 			for(k = 0; k < 3; k++) 				decrypt[i][j] = decrypt[i][j] + b[i][k] * encrypt[k][j]; 	 	printf("\nDecrypted string is: "); 	for(i = 0; i < 3; i++) 		printf("%c", (char)(fmod(decrypt[i][0], 26) + 97)); 	 	printf("\n"); }   void getKeyMessage() { 	int i, j; 	char msg[3];   	printf("Enter 3x3 matrix for key (It should be inversible):\n"); 	 	for(i = 0; i < 3; i++) 		for(j = 0; j < 3; j++) { 			scanf("%f", &a[i][j]); 			c[i][j] = a[i][j]; 		} 	 	printf("\nEnter a 3 letter string: "); 	scanf("%s", msg); 	 	for(i = 0; i < 3; i++) 		mes[i][0] = msg[i] - 97; }   void inverse() { 	int i, j, k; 	float p, q; 	 	for(i = 0; i < 3; i++) 		for(j = 0; j < 3; j++) { 			if(i == j) 				b[i][j]=1; 			else 				b[i][j]=0; 		} 		 	for(k = 0; k < 3; k++) { 		for(i = 0; i < 3; i++) { 			p = c[i][k]; 			q = c[k][k]; 				 			for(j = 0; j < 3; j++) { 				if(i != k) { 					c[i][j] = c[i][j]*q - p*c[k][j]; 					b[i][j] = b[i][j]*q - p*b[k][j]; 				} 			} 		} 	} 	 	for(i = 0; i < 3; i++) 		for(j = 0; j < 3; j++) 			b[i][j] = b[i][j] / c[i][i]; 	 	printf("\n\nInverse Matrix is:\n"); 	for(i = 0; i < 3; i++) { 		for(j = 0; j < 3; j++) 			printf("%d ", b[i][j]); 		 		printf("\n"); 	} }