SIMPLE ALGORITHME DE CRYPTAGE

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

//By Mat000

int main(int argc, char* argv[])
{
	char answer[3];

	begin:

	printf("\n\n(C)rypt or (D)ecrypt ? : ");
	fgets(answer, 2, stdin); //Fonction sécurisée (buffer overflow)

	fflush(stdin);

	if(answer[0] == 'C' || answer[0] == 'c')
		crypt();

	if(answer[0] == 'D' || answer[0] == 'd')
		decrypt();

	goto begin;

	return 1;
}

int getstringsum(char* string, int len) //Cette fonction additionne les valeurs ASCII des caractères d'un string entre eux.
{
	int i, sum = 0;

	for(i=0;i<len;i++)
	{
		sum += string[i];
	}

	return sum;
}

int crypt()
{
	int i, j = 0, k, l;
	FILE* passfile;
	char text[1000] = {'/0'};
	char pass[1000] = {'/0'};

	printf("\nText to crypt: ");
	fgets(&text, 1000, stdin);

        if(text[0] == '/0')
        	return 0;

	printf("Now, the password: ");
	fgets(&pass, 1000, stdin);
        if(pass[0] == '/0')
        	return 0;

	k = strlen(&pass);
	l = strlen(&text);

	for(i=0;i<l;i++)
	{
		text[i] += pass[j] + getstringsum(&pass, k); // ici on calcule la phrase de base (ex: "abc123") + le pass ("123") + getstringsum("123") ce qui donne a+1+(1+2+3), b + 2 + (1+2+3), c+3+(1+2+3), 1 + 1+(1+2+3), etc...
		j++;
		if(j == k)
			j = 0;
	}

	printf("\nPass crypted : %s\n", text);

	passfile = fopen("C:\\passcrypted.txt", "w");

	if(passfile == NULL)
	{
		printf("Opening file failed.\n");
		return 0;
	}

	fprintf(passfile, "%s", text);

	printf("Crypted text written in file.\n");

	fclose(passfile);

	return 1;
}

int decrypt()
{
	int i, j = 0, k, l;
	FILE* passfile;
	char text[1000] = {'/0'};
	char pass[1000] = {'/0'};

	printf("\nRetrieving text crypted...\n");

	passfile = fopen("C:\\passcrypted.txt", "r");

	if(passfile == NULL)
	{
		printf("C:\\passfile.txt doesn't exist.");
		return 0;
	}

	fgets(&text, 1000, passfile); //On recupere la phrase cryptée dans le fichier "C:\passfile.txt"
	printf("Text retrieved : %s\n", text);

	printf("Then decrypt with the pass : ");
	fgets(&pass, 1000, stdin);

	k = strlen(&pass);
	l = strlen(&text);

	for(i=0;i<l;i++)
	{
		text[i] -= pass[j] + getstringsum(&pass, k); // Pareil sauf que cette fois on inverse la méthode
		j++;
		if(j == k)
			j = 0;
	}

	printf("\nText decrypted : %s\n", text);

	fclose(passfile);

	return 1;
}