CueCat decoder

cuecat.c

/*
 * CueCat Decoder
 *
 * Thanks to:
 *   - http://oilcan.org/cuecat/base64.html
 *   - LibraryThing for shipping my CueCat
 *
 * Copyright (c) 2009 Ricardo Martins <ricardo@scarybox.net>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 */

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

#define XOR 'C'

const char *base64 = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789+-";

char *decode64(const char *orig)
{
    int i, j;
    size_t length = strlen(orig);
    char *in, *out, *head;
    union x {
        char data[3];
        int as_integer;
    } alpha;

    in = malloc(length - (length%4) + 4 + 1);
    memset(in, '=', length - (length%4) + 4);
    strcpy(in, orig);

    out = calloc(length+1, sizeof(char));
    head = out;

    for (i = 0; i < length; i++) {
        for (j = 0; in[i] != '=' && in[i] != base64[j]; j++);
        in[i] = j;
    }

    for (i = 0; i < length; i += 4) {
        alpha.as_integer = in[i] << 18;
        alpha.as_integer |= in[i+1] << 12;
        alpha.as_integer |= in[i+2] << 6;
        alpha.as_integer |= in[i+3];
        *(head++) = alpha.data[2];
        *(head++) = alpha.data[1];
        *(head++) = alpha.data[0];
    }
    *head = 0;

    free(in);

    return out;
}

/*
 * Returns just the barcode data, ignoring the CueCat's serial number and the
 * type of the barcode
 */
static char *getData(const char *input)
{
    int nSeen;
    char *data;
    const char *pos = NULL;

    for (nSeen = 0; *input != '\0'; input++) {
        if (*input == '.') {
            nSeen++;
            if (nSeen == 3)
                pos = input + 1;
        }
    }

    assert(pos != NULL);

    size_t size = input - pos - 1;
    data = calloc(size+1, sizeof(char));
    strncpy(data, pos, size);

    return data;
}

/* Decodes the data encrypted by the CueCat */
static char *decode(char *in)
{
    int i;
    char *decoded = decode64(in);

    for (i = 0; i < strlen(decoded); i++) {
        decoded[i] ^= XOR;
    }

    return decoded;
}

int main(void)
{
    char *input, *data, *decoded;

    input = calloc(255, sizeof(char));
    scanf("%254s", input);

    data = getData(input);
    decoded = decode(data);
    printf("%s\n", decoded);

    free(input);
    free(data);
    free(decoded);

    return 0;
}

// vim: et ts=4 sw=4 sts=4

cuecat.rb

#!/usr/bin/env ruby
#
# (C)opyright 2009 Ricardo Martins <ricardo at scarybox dot net>
# Licensed under the MIT/X11 License. See LICENSE file for license details.

require 'base64'

def decode(str)
    data = str.split('.')[3]
    dec64 = Base64.decode64(data.swapcase)
    decoded = String.new
    dec64.each_byte {|i| decoded << (i^'C'[0]) }
    return decoded
end

input = gets
puts decode(input)