ascon-prng.c

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/*
 * Copyright (C) 2022 Southern Storm Software, Pty Ltd.
 *
 * 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 <ascon/random.h>
#include <ascon/utility.h>
#include "random/ascon-trng.h"
#include "core/ascon-util-snp.h"
 
#define ASCON_RANDOM_RESEED_LIMIT 16384
 
static void ascon_random_rekey(ascon_random_state_t *state)
{
    int temp;
 
    /* Zero out part of the state and run the permutation several times.
     * This enforces forward security on the SpongePRNG state. */
    ascon_xof_pad(&(state->xof));
    ascon_acquire(&(state->xof.state));
    for (temp = 0; temp < (40 - ASCON_XOF_RATE); temp += ASCON_XOF_RATE) {
        ascon_overwrite_with_zeroes(&(state->xof.state), 0, ASCON_XOF_RATE);
        ascon_permute(&(state->xof.state), 0);
    }
    ascon_release(&(state->xof.state));
}
 
int ascon_random_init(ascon_random_state_t *state)
{
    unsigned char seed[ASCON_SYSTEM_SEED_SIZE];
    int ok;
    if (!state)
        return 0;
    ascon_xof_init_custom(&(state->xof), "SpongePRNG", 0, 0, 0);
    state->counter = 0;
    state->reserved = 0;
    ok = ascon_trng_generate(seed, sizeof(seed));
    ascon_xof_absorb(&(state->xof), seed, sizeof(seed));
    ascon_clean(seed, sizeof(seed));
    ascon_random_rekey(state);
    return ok;
}
 
void ascon_random_free(ascon_random_state_t *state)
{
    if (state) {
        state->counter = 0;
        ascon_xof_free(&(state->xof));
    }
}
 
void ascon_random_fetch
    (ascon_random_state_t *state, unsigned char *out, size_t outlen)
{
    /* If there is no state, use the global ascon_random() function
     * so that we return something.  Safer than returning nothing
     * to the caller by accident and having them use that nothing. */
    if (!state) {
        ascon_random(out, outlen);
        return;
    }
 
    /* Force a re-seed if we have generated too many bytes so far */
    if (state->counter >= ASCON_RANDOM_RESEED_LIMIT)
        ascon_random_reseed(state);
 
    /* Squeeze data out of the PRNG state */
    ascon_xof_squeeze(&(state->xof), out, outlen);
    if (outlen < ASCON_RANDOM_RESEED_LIMIT)
        state->counter += outlen;
    else
        state->counter = ASCON_RANDOM_RESEED_LIMIT;
 
    /* Re-key the PRNG to enforce forward security */
    ascon_random_rekey(state);
}
 
int ascon_random_reseed(ascon_random_state_t *state)
{
    if (state) {
        /* Generate a new system seed and absorb it into the state */
        unsigned char seed[ASCON_SYSTEM_SEED_SIZE];
        int ok = ascon_trng_generate(seed, sizeof(seed));
        ascon_xof_absorb(&(state->xof), seed, sizeof(seed));
        ascon_clean(seed, sizeof(seed));
 
        /* Reset the re-seed counter to 0 */
        state->counter = 0;
 
        /* Re-key the PRNG to enforce forward security */
        ascon_random_rekey(state);
        return ok;
    }
    return 0;
}
 
void ascon_random_feed
    (ascon_random_state_t *state, const unsigned char *entropy, size_t size)
{
    if (state) {
        ascon_xof_absorb(&(state->xof), entropy, size);
        ascon_xof_pad(&(state->xof));
        ascon_random_rekey(state);
    }
}