vignere encryption

vignere.c

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

#define OFFSET 97

int main(int argc, char* argv[])
{
	char* klartext;
	char* geheimtext;
	char* schluessel;
	int counter;
	int laenge;

	if(argc != 3)
	{
		printf("Falsche Parameter\n");
		return EXIT_FAILURE;
	}

	klartext = (char*)strdup(argv[1]);
	geheimtext = (char*)malloc(sizeof(klartext));
	schluessel = (char*)strdup(argv[2]);
	laenge = strlen(klartext);
	
	for(counter = 0; counter < laenge; counter++)
	{
		char c = klartext[counter];
		int offset = (int)schluessel[counter % strlen(schluessel)] - OFFSET;
		c = (char)((((((int)c) - OFFSET) + offset) % 26) + OFFSET);
		geheimtext[counter] = c;
	}

	printf("Klartext: %s \n", klartext);
	printf("Geheimtext: %s \n", geheimtext);


	return EXIT_SUCCESS;
}