File xorer

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

typedef unsigned char byte;

byte *xordata(byte *data1, byte *data2, int size);
void xorfile(FILE *input, FILE *output, byte *key, int key_size);
int datalength(byte *data);

int main(int argc, char **argv){
    //Bad arguments
        if( argc < 2){
            printf("No input files.\n\nUse: xorer [file] [key file]\n");
            return -1;
        }else if( argc < 3){
            printf("No  key file introduced.\n\nUse: xorer [file] [key file]\n");
            return -1;
        }
    //Open the files
        FILE *input;
        FILE *output;
        FILE *file_key;

        printf("\nInput file: %s\n\nKey file: %s", argv[1], argv[2]);

        input    = fopen(argv[1], "rb");
        file_key = fopen(argv[2], "rb");
        output   = fopen("output.bin", "wb");
    //Get the key and calculate its size
        fseek(file_key, 0, SEEK_END);
        int key_size = ftell(file_key);

        fseek(file_key, 0, SEEK_SET);
        byte *key = (byte *)malloc(key_size);
        fread(key, 1, key_size, file_key);

        printf("\n\nThe key is %i byte(s) long", key_size);
    //Algorithm
        xorfile(input, output, key, key_size);


    fclose(input);
    fclose(output);
    return 0;
}


byte *xordata(byte *data1, byte *data2, int size){
    int i;
    byte *out = (byte *)malloc(size);
    for(i = 0; i<size; i++){
        out[i] = data1[i] ^ data2[i];
    }
    return out;
}

void xorfile(FILE *input, FILE *output, byte *key, int key_size){
    int i, steps, input_file_size;
    byte *buffer = (byte *)malloc(key_size);
    byte *out    = (byte *)malloc(key_size);
    //Calculate input file size
        fseek(input, 0, SEEK_END);
        input_file_size = ftell(input);
        fseek(input, 0, SEEK_SET);
    //Calculate steps
        steps = (input_file_size/key_size);
        printf("\n\nThe input file is %i bytes(s) long, so I have to do %i step(s) for xoring the file.\n\nxoring file, please wait...", input_file_size, steps);
    //Algorithm!
        for(i = 0; i< steps; i++){
            fread(buffer, 1, key_size, input);
            out = xordata(buffer, key, key_size);
            fwrite(out, 1, key_size, output);
        }
        printf("\n\nFile xored succesfully!!\n");
}

int datalength(byte *data){
    int length = 0;
    while(*data++)
        length++;
    return length;
}