Simple C Program for Encrypting/Decrypting Basic Files

encrypt.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>

#define MAXIN 250

void encrypt(char *, int);
void decrypt(char *, int);
void prompt(const char*, char*);

int main() {

	printf("\n++++[1]> Encrypt ++++\n");
	printf("++++[2]> Decrypt ++++\n");
	printf("++++[0]> exit ++++\n\n");

	
	char choice[MAXIN];
	prompt("++[>]Enter choice: ", choice);
	if(atoi(choice) != 0 && atoi(choice) != 1 && atoi(choice) != 2) {
	
		printf("Invalid option\n");
		exit(1);
		
	}
	if(atoi(choice) == 0)
		exit(0);
	
	char input_file[MAXIN], chkey[MAXIN];
	int key;
	
	//Get the target file path for encryption/decrytion
	
	prompt("++[>]File path: ", input_file);
	
	//Use a key
	prompt("++[>]Key: ", chkey);
	
	//convert the key character to an int value;
	
	key = atoi(chkey);
	if(!key) {
		printf("Encryption/Decrytion key must be an integer value!\n");
		exit(1);
	}
	
	if(atoi(choice) == 1)
		encrypt(input_file, key);
	else
		decrypt(input_file, key);
		
	return 0;
}
void prompt(const char *prompt, char *buffer) {
	
	printf("%s", prompt);
	buffer[0] = 0;
	
	fgets(buffer, MAXIN, stdin);
	
	const int isize = strlen(buffer);
	if(isize > 0)
		buffer[isize - 1] = 0;
	
}

void encrypt(char *filename, int key) {

	FILE *target, *output;
	char output_file[MAXIN];
	
	prompt("++[>]Enter output filename: ", output_file);

	target = fopen(filename, "r");
	
	if(target == NULL) {
		fprintf(stderr, "Error reading file %s (%s)\n", filename, strerror(errno));
		exit(1);
	}
	
	output = fopen(output_file, "w");
	if(output == NULL) {
		fprintf(stderr, "Error creating/opening file %s (%s)\n", output_file, strerror(errno));
		exit(1);
	}
	printf("++Encrypting file....\n");
	char ch;
	
	//Read the file char by char as long as it does reach to the end
	
	ch = fgetc(target);
	while(ch != EOF) {
		char tmp;
		tmp = ch + key;
		fprintf(output, "%c", tmp);
		 printf("%c", ch);
		ch = fgetc(target);
	}
	
	printf("++Encrption complete [✔]");
	fclose(target);
	fclose(output);
}



void decrypt(char *filename, int key) {

	FILE *target, *output;
	char output_file[MAXIN];
	
	prompt("++[>]Enter output filename: ", output_file);

	target = fopen(filename, "r");
	
	if(target == NULL) {
		fprintf(stderr, "Error reading file %s (%s)\n", filename, strerror(errno));
		exit(1);
	}
	
	output = fopen(output_file, "w");
	if(output == NULL) {
		fprintf(stderr, "Error creating/opening file %s (%s)\n", output_file, strerror(errno));
		exit(1);
	}
	printf("++Decrypting file....\n");
	char ch;
	
	//Read the file char by char as long as it does reach to the end
	
	ch = fgetc(target);
	while(ch != EOF) {
		char tmp;
		memset(&tmp, 0, sizeof(tmp));
		tmp = ch - key;
		fprintf(output, "%c", tmp);
		 
		ch = fgetc(target);
	}
	
	printf("++Decrption complete [✔]");
	fclose(target);
	fclose(output);
}