gistfile1.c

#include <sodium.h>
#include <stdio.h>

#define CLIENT_ID_SIZE crypto_box_PUBLICKEYBYTES

/* Copied over from DHT.c not to mess around with tox source deps */
int id_closest(const uint8_t *id, const uint8_t *id1, const uint8_t *id2)
{
    size_t   i;
    uint8_t distance1, distance2;

    for (i = 0; i < CLIENT_ID_SIZE; ++i) {

        distance1 = abs(((int8_t *)id)[i] ^ ((int8_t *)id1)[i]);
        distance2 = abs(((int8_t *)id)[i] ^ ((int8_t *)id2)[i]);

        if (distance1 < distance2)
            return 1;

        if (distance1 > distance2)
            return 2;
    }

    return 0;
}


int main()
{
    long tries=0;
    uint8_t pA[crypto_box_PUBLICKEYBYTES], sA[crypto_box_SECRETKEYBYTES];
    uint8_t pB[crypto_box_PUBLICKEYBYTES], sB[crypto_box_SECRETKEYBYTES];
    uint8_t pC[crypto_box_PUBLICKEYBYTES], sC[crypto_box_SECRETKEYBYTES];
    
    /* Generating an initial pair */
    crypto_box_keypair(pA, sA);
    crypto_box_keypair(pB, sB);
    
    do
    {
        crypto_box_keypair(pC, sC);
        tries++;
    }
    while (id_closest(pA, pB, pC) != 2);
    
    printf("Found a closer key after %ld tries\n", tries);
    
    return 0;
}