/* experiment with precomputed attack */
/* overwrites files in out/ */

/* mkdir out; gcc -O3 -lcrypto ossl7.c && (ulimit -S -n 1040 && time ./a.out) */

/*
 * Copyright © 2021 Aleksey Cherepanov <lyosha@openwall.com>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted.
 */

#pragma GCC diagnostic ignored "-Wdeclaration-after-statement"
#pragma GCC optimize 3

#include <stdio.h>
#include <openssl/md5.h>
#include <string.h>
#include <assert.h>
#include <stdlib.h>

/* index of candidate to static hash buffer */
unsigned char *get_hash(int idx)
{
    /* index to candidate */
    char buf[21];
    sprintf(buf, "%d", idx);
    /* candidate to hash */
    MD5_CTX ctx;
    static unsigned char hash_out[MD5_DIGEST_LENGTH];
    MD5_Init(&ctx);
    MD5_Update(&ctx, buf, strlen(buf));
    MD5_Final(hash_out, &ctx);
    return hash_out;
}

/* globals */
#define groups_k 1024

FILE *files[groups_k] = { 0 };

int main(void)
{
    char buf[32];
    for (int i = 0; i < groups_k; i++) {
        sprintf(buf, "out/%d", i);
        files[i] = fopen(buf, "w");
        assert(files[i]);
    }

    for (int i = 0; i < 256 * 256 * 256; i++) {
        unsigned char *h = get_hash(i);
        int group = (h[0] * 256 + h[1]) % groups_k;
        int r = fwrite(&i, sizeof(i), 1, files[group]);
        assert(r == 1);
    }

    for (int i = 0; i < groups_k; i++) {
        int r = fclose(files[i]);
        assert(r == 0);
    }

    return 0;
}