/*
* Simple string obfuscation - Quequero 2013
*
* Obfuscated string format:
* 1-byte key. 1-byte module. 1-byte length, <string>
*/

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

// <search string> <replace string> <string to search>
unsigned char *str_replace(unsigned char *search , unsigned char *replace , unsigned char *subject) {
    unsigned char *p = NULL , *old = NULL , *new_subject = NULL ;
    int c = 0 , search_size;

    search_size = strlen(search);

    for (p = strstr(subject , search) ; p != NULL ; p = strstr(p + search_size , search)) {
        c++;
    }

    c = (strlen(replace) - search_size )*c + strlen(subject);
    new_subject = malloc(c);
    strcpy(new_subject , "");
    old = subject;

    for (p = strstr(subject , search) ; p != NULL ; p = strstr(p + search_size , search)) {
        strncpy(new_subject + strlen(new_subject) , old , p - old);
        strcpy(new_subject + strlen(new_subject) , replace);
        old = p + search_size;
    }

    strcpy(new_subject + strlen(new_subject) , old);
    return new_subject;
}

int obfuscate(unsigned char *s, unsigned char *d) {
    unsigned int seed;
    unsigned char key, mod;
    unsigned char *rep = NULL;
    unsigned char nl[] = "\n";
    unsigned char tb[] = "\t";
    unsigned char cr[] = "\r";
    int i, j, len;

    srandom(time(0));
    seed = random();

    key = (unsigned char)(seed & 0x000000ff);
    mod = (unsigned char)((seed & 0x0000ff00) >> 8);

    rep = str_replace("\\n", nl, s);
    rep = str_replace("\\t", tb, rep);
    rep = str_replace("\\r", cr, rep);

    len = strlen(rep);

    if (len > 255) {
        printf("String too long\n");
        return;
    }

    d[0] = key;
    d[1] = mod;
    d[2] = (unsigned char)len ^ key ^ mod;

    for (i = 0, j = 3; i < len; i++, j++) {
        d[j] = rep[i] ^ key;
        d[j] += mod;
        d[j] ^= mod;
    }

    return len;
}

unsigned char* deobfuscate(unsigned char *s) {
    unsigned char key, mod, len;
    int i, j;
    static unsigned char d[256]; // E' zozza ma cosi' non serve la free()

    key = s[0];
    mod = s[1];
    len = s[2] ^ key ^ mod;

    // zero terminate the string
    memset(d, 0x00, len + 1);

    for (i = 0, j = 3; i < len; i++, j++) {
        d[i] = s[j] ^ mod;
        d[i] -= mod;
        d[i] ^= key;
    }

    d[len] = 0;
    return d;
}

int main(int argc, char *argv[]) {
    unsigned char *buf, *test;
    int i, obf_len;

    if (argc < 2) {
        printf("Usage: %s <string>\n", argv[0]);
        return 0;
    }

    if (strlen(argv[1]) > 255) {
        printf("String too long\n");
        return 0;
    }

    obf_len = strlen(argv[1]) + 3;

    buf = (unsigned char *)malloc(obf_len);
    memset(buf, 0x00, obf_len);

    obf_len = obfuscate(argv[1], buf);
    obf_len += 3;

    printf("unsigned char obf_string[] = \"");

    for (i = 0; i < obf_len; i++) {
        printf("\\x");
        printf("%02x", buf[i]);
    }

    printf("\"; // \"%s\"\n", argv[1]);

    test = deobfuscate(buf);

    printf("Deobfuscated string: \"%s\"\n", test);

    free(buf);
    return 0;
}