Hill Cipher in C and C++ (Encryption and Decryption)

Here you get encryption and decryption program for hill cipher in C and C++.

What is Hill Cipher?

In cryptography (field identified with encryption-decryption) hill cypher is a polygraphic

cipher dependent on a direct variable based math. Imagined by Lester S. Hill in 1929

and in this manner got its name. It was the principal cipher that had the option to work on 3 images without a moment’s delay.

Encryption: The given message string and the key string is spoken to as a framework.

At that point key and message, framework are increased. At long last modulo 26

is taken for every component of the network got by the increase. The key framework that we take here ought to be

invertible, generally, decryption won’t be conceivable.

Decryption: The scrambled message lattice is increased by the converse of key framework lastly its modulo 26 is taken to get the first message.

Hill Cipher Program 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");
	}
}

hill Cipher Program in C++

#include<iostream>
#include<math.h>
 
using namespace std;
 
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
 
int 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];
	
	cout<<"\nEncrypted string is: ";
	for(i = 0; i < 3; i++)
		cout<<(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];
	
	cout<<"\nDecrypted string is: ";
	for(i = 0; i < 3; i++)
		cout<<(char)(fmod(decrypt[i][0], 26) + 97);
	
	cout<<"\n";
}
 
void getKeyMessage() {
	int i, j;
	char msg[3];
 
	cout<<"Enter 3x3 matrix for key (It should be inversible):\n";
	
	for(i = 0; i < 3; i++)
		for(j = 0; j < 3; j++) {
			cin>>a[i][j];
			c[i][j] = a[i][j];
		}
	
	cout<<"\nEnter a 3 letter string: ";
	cin>>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];
	
	cout<<"\n\nInverse Matrix is:\n";
	for(i = 0; i < 3; i++) {
		for(j = 0; j < 3; j++)
			cout<<b[i][j]<<" ";
		
		cout<<"\n";
	}
}

Output

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