c-toxcore/toxcore/crypto_core.c

/* net_crypto.c
 *
 * Functions for the core crypto.
 *
 * NOTE: This code has to be perfect. We don't mess around with encryption.
 *
 *  Copyright (C) 2013 Tox project All Rights Reserved.
 *
 *  This file is part of Tox.
 *
 *  Tox is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  Tox is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with Tox.  If not, see <http://www.gnu.org/licenses/>.
 *
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include "crypto_core.h"

#if crypto_box_PUBLICKEYBYTES != 32
#error crypto_box_PUBLICKEYBYTES is required to be 32 bytes for public_key_cmp to work,
#endif

/* compare 2 public keys of length crypto_box_PUBLICKEYBYTES, not vulnerable to timing attacks.
   returns 0 if both mem locations of length are equal,
   return -1 if they are not. */
int public_key_cmp(const uint8_t *pk1, const uint8_t *pk2)
{
    return crypto_verify_32(pk1, pk2);
}

/*  return a random number.
 */
uint32_t random_int(void)
{
    uint32_t randnum;
    randombytes((uint8_t *)&randnum , sizeof(randnum));
    return randnum;
}

uint64_t random_64b(void)
{
    uint64_t randnum;
    randombytes((uint8_t *)&randnum, sizeof(randnum));
    return randnum;
}

/* Check if a Tox public key crypto_box_PUBLICKEYBYTES is valid or not.
 * This should only be used for input validation.
 *
 * return 0 if it isn't.
 * return 1 if it is.
 */
int public_key_valid(const uint8_t *public_key)
{
    if (public_key[31] >= 128) { /* Last bit of key is always zero. */
        return 0;
    }

    return 1;
}

/* Precomputes the shared key from their public_key and our secret_key.
 * This way we can avoid an expensive elliptic curve scalar multiply for each
 * encrypt/decrypt operation.
 * enc_key has to be crypto_box_BEFORENMBYTES bytes long.
 */
int encrypt_precompute(const uint8_t *public_key, const uint8_t *secret_key, uint8_t *enc_key)
{
    return crypto_box_beforenm(enc_key, public_key, secret_key);
}

int encrypt_data_symmetric(const uint8_t *secret_key, const uint8_t *nonce, const uint8_t *plain, uint32_t length,
                           uint8_t *encrypted)
{
    if (length == 0 || !secret_key || !nonce || !plain || !encrypted) {
        return -1;
    }

    uint8_t temp_plain[length + crypto_box_ZEROBYTES];
    uint8_t temp_encrypted[length + crypto_box_MACBYTES + crypto_box_BOXZEROBYTES];

    memset(temp_plain, 0, crypto_box_ZEROBYTES);
    memcpy(temp_plain + crypto_box_ZEROBYTES, plain, length); // Pad the message with 32 0 bytes.

    if (crypto_box_afternm(temp_encrypted, temp_plain, length + crypto_box_ZEROBYTES, nonce, secret_key) != 0) {
        return -1;
    }

    /* Unpad the encrypted message. */
    memcpy(encrypted, temp_encrypted + crypto_box_BOXZEROBYTES, length + crypto_box_MACBYTES);
    return length + crypto_box_MACBYTES;
}

int decrypt_data_symmetric(const uint8_t *secret_key, const uint8_t *nonce, const uint8_t *encrypted, uint32_t length,
                           uint8_t *plain)
{
    if (length <= crypto_box_BOXZEROBYTES || !secret_key || !nonce || !encrypted || !plain) {
        return -1;
    }

    uint8_t temp_plain[length + crypto_box_ZEROBYTES];
    uint8_t temp_encrypted[length + crypto_box_BOXZEROBYTES];

    memset(temp_encrypted, 0, crypto_box_BOXZEROBYTES);
    memcpy(temp_encrypted + crypto_box_BOXZEROBYTES, encrypted, length); // Pad the message with 16 0 bytes.

    if (crypto_box_open_afternm(temp_plain, temp_encrypted, length + crypto_box_BOXZEROBYTES, nonce, secret_key) != 0) {
        return -1;
    }

    memcpy(plain, temp_plain + crypto_box_ZEROBYTES, length - crypto_box_MACBYTES);
    return length - crypto_box_MACBYTES;
}

int encrypt_data(const uint8_t *public_key, const uint8_t *secret_key, const uint8_t *nonce,
                 const uint8_t *plain, uint32_t length, uint8_t *encrypted)
{
    if (!public_key || !secret_key) {
        return -1;
    }

    uint8_t k[crypto_box_BEFORENMBYTES];
    encrypt_precompute(public_key, secret_key, k);
    int ret = encrypt_data_symmetric(k, nonce, plain, length, encrypted);
    sodium_memzero(k, sizeof k);
    return ret;
}

int decrypt_data(const uint8_t *public_key, const uint8_t *secret_key, const uint8_t *nonce,
                 const uint8_t *encrypted, uint32_t length, uint8_t *plain)
{
    if (!public_key || !secret_key) {
        return -1;
    }

    uint8_t k[crypto_box_BEFORENMBYTES];
    encrypt_precompute(public_key, secret_key, k);
    int ret = decrypt_data_symmetric(k, nonce, encrypted, length, plain);
    sodium_memzero(k, sizeof k);
    return ret;
}


/* Increment the given nonce by 1. */
void increment_nonce(uint8_t *nonce)
{
    /* TODO(irungentoo): use increment_nonce_number(nonce, 1) or sodium_increment (change to little endian)
     * NOTE don't use breaks inside this loop
     * In particular, make sure, as far as possible,
     * that loop bounds and their potential underflow or overflow
     * are independent of user-controlled input (you may have heard of the Heartbleed bug).
     */
    uint32_t i = crypto_box_NONCEBYTES;
    uint_fast16_t carry = 1U;

    for (; i != 0; --i) {
        carry += (uint_fast16_t) nonce[i - 1];
        nonce[i - 1] = (uint8_t) carry;
        carry >>= 8;
    }
}
/* increment the given nonce by num */
void increment_nonce_number(uint8_t *nonce, uint32_t host_order_num)
{
    /* NOTE don't use breaks inside this loop
     * In particular, make sure, as far as possible,
     * that loop bounds and their potential underflow or overflow
     * are independent of user-controlled input (you may have heard of the Heartbleed bug).
     */
    const uint32_t big_endian_num = htonl(host_order_num);
    const uint8_t *const num_vec = (const uint8_t *) &big_endian_num;
    uint8_t num_as_nonce[crypto_box_NONCEBYTES] = {0};
    num_as_nonce[crypto_box_NONCEBYTES - 4] = num_vec[0];
    num_as_nonce[crypto_box_NONCEBYTES - 3] = num_vec[1];
    num_as_nonce[crypto_box_NONCEBYTES - 2] = num_vec[2];
    num_as_nonce[crypto_box_NONCEBYTES - 1] = num_vec[3];

    uint32_t i = crypto_box_NONCEBYTES;
    uint_fast16_t carry = 0U;

    for (; i != 0; --i) {
        carry += (uint_fast16_t) nonce[i - 1] + (uint_fast16_t) num_as_nonce[i - 1];
        nonce[i - 1] = (unsigned char) carry;
        carry >>= 8;
    }
}

/* Fill the given nonce with random bytes. */
void random_nonce(uint8_t *nonce)
{
    randombytes(nonce, crypto_box_NONCEBYTES);
}

/* Fill a key crypto_box_KEYBYTES big with random bytes */
void new_symmetric_key(uint8_t *key)
{
    randombytes(key, crypto_box_KEYBYTES);
}