oqs-sys 0.11.0+liboqs-0.13.0

// SPDX-License-Identifier: (Apache-2.0 OR MIT) AND CC0-1.0
#include <stdint.h>
#include <string.h>

#include "utils.h"
#include "hash.h"
#include "wots.h"
#include "hash_address.h"
#include "params.h"

/**
 * Helper method for pseudorandom key generation.
 * Expands an n-byte array into a len*n byte array using the `prf_keygen` function.
 */
static void expand_seed(const xmss_params *params,
                        unsigned char *outseeds, const unsigned char *inseed,
                        const unsigned char *pub_seed, uint32_t addr[8],
                        unsigned char *buf)
{
    unsigned int i;
    unsigned char *prf_buf = buf + params->n + 32;

    set_hash_addr(addr, 0);
    set_key_and_mask(addr, 0);
    memcpy(buf, pub_seed, params->n);
    for (i = 0; i < params->wots_len; i++) {
        set_chain_addr(addr, i);
        addr_to_bytes(buf + params->n, addr);
        prf_keygen(params, outseeds + i*params->n, buf, inseed, prf_buf);
    }
}

/**
 * Computes the chaining function.
 * out and in have to be n-byte arrays.
 *
 * Interprets in as start-th value of the chain.
 * addr has to contain the address of the chain.
 */
static void gen_chain(const xmss_params *params,
                      unsigned char *out, const unsigned char *in,
                      unsigned int start, unsigned int steps,
                      const unsigned char *pub_seed, uint32_t addr[8],
                      unsigned char *thash_buf)
{
    unsigned int i;

    /* Initialize out with the value at position 'start'. */
    memcpy(out, in, params->n);

    /* Iterate 'steps' calls to the hash function. */
    for (i = start; i < (start+steps) && i < params->wots_w; i++) {
        set_hash_addr(addr, i);
        thash_f(params, out, out, pub_seed, addr, thash_buf);
    }
}

/**
 * base_w algorithm as described in draft.
 * Interprets an array of bytes as integers in base w.
 * This only works when log_w is a divisor of 8.
 */
static void base_w(const xmss_params *params,
                   unsigned int *output, const unsigned int out_len, const unsigned char *input)
{
    unsigned int in = 0;
    unsigned int out = 0;
    unsigned char total;
    unsigned int bits = 0;
    unsigned int consumed;

    for (consumed = 0; consumed < out_len; consumed++) {
        if (bits == 0) {
            total = input[in];
            in++;
            bits += 8;
        }
        bits -= params->wots_log_w;
        output[out] = (total >> bits) & (params->wots_w - 1);
        out++;
    }
}

/* Computes the WOTS+ checksum over a message (in base_w). */
static void wots_checksum(const xmss_params *params,
                          unsigned int *csum_base_w, const unsigned int *msg_base_w)
{
    int csum = 0;
    unsigned int csum_bytes_length =  (params->wots_len2 * params->wots_log_w + 7) / 8;
    unsigned char *csum_bytes = OQS_MEM_malloc(csum_bytes_length);
    if (csum_bytes == NULL) {
        return;
    }
    unsigned int i;

    /* Compute checksum. */
    for (i = 0; i < params->wots_len1; i++) {
        csum += params->wots_w - 1 - msg_base_w[i];
    }

    /* Convert checksum to base_w. */
    /* Make sure expected empty zero bits are the least significant bits. */
    csum = csum << (8 - ((params->wots_len2 * params->wots_log_w) % 8));
    ull_to_bytes(csum_bytes, csum_bytes_length, csum);
    base_w(params, csum_base_w, params->wots_len2, csum_bytes);

    OQS_MEM_insecure_free(csum_bytes);
}

/* Takes a message and derives the matching chain lengths. */
static void chain_lengths(const xmss_params *params,
                          unsigned int *lengths, const unsigned char *msg)
{
    base_w(params, lengths, params->wots_len1, msg);
    wots_checksum(params, lengths + params->wots_len1, lengths);
}

/**
 * WOTS key generation. Takes a 32 byte seed for the private key, expands it to
 * a full WOTS private key and computes the corresponding public key.
 * It requires the seed pub_seed (used to generate bitmasks and hash keys)
 * and the address of this WOTS key pair.
 *
 * Writes the computed public key to 'pk'.
 */
void wots_pkgen(const xmss_params *params,
                unsigned char *pk, const unsigned char *seed,
                const unsigned char *pub_seed, uint32_t addr[8])
{
    unsigned int i;
    const size_t buf_size = 2 * params->padding_len + 4 * params->n + 64;
    unsigned char *buf = OQS_MEM_malloc(buf_size);
    if (buf == NULL) {
        return;
    }
    
    /* The WOTS+ private key is derived from the seed. */
    expand_seed(params, pk, seed, pub_seed, addr, buf);

    for (i = 0; i < params->wots_len; i++) {
        set_chain_addr(addr, i);
        gen_chain(params, pk + i*params->n, pk + i*params->n,
                  0, params->wots_w - 1, pub_seed, addr, buf);
    }

    OQS_MEM_secure_free(buf, buf_size);
}

/**
 * Takes a n-byte message and the 32-byte seed for the private key to compute a
 * signature that is placed at 'sig'.
 */
void wots_sign(const xmss_params *params,
               unsigned char *sig, const unsigned char *msg,
               const unsigned char *seed, const unsigned char *pub_seed,
               uint32_t addr[8])
{
    const size_t buf_size = 2 * params->padding_len + 4 * params->n + 64;
    unsigned int *lengths = OQS_MEM_calloc(params->wots_len, sizeof(unsigned int));
    unsigned char *buf = OQS_MEM_malloc(buf_size);
    unsigned int i;
    if (lengths == NULL || buf == NULL) {
        return;
    }

    chain_lengths(params, lengths, msg);

    /* The WOTS+ private key is derived from the seed. */
    expand_seed(params, sig, seed, pub_seed, addr, buf);

    for (i = 0; i < params->wots_len; i++) {
        set_chain_addr(addr, i);
        gen_chain(params, sig + i*params->n, sig + i*params->n,
                  0, lengths[i], pub_seed, addr, buf);
    }

    OQS_MEM_insecure_free(lengths);
    OQS_MEM_secure_free(buf, buf_size);
}

/**
 * Takes a WOTS signature and an n-byte message, computes a WOTS public key.
 *
 * Writes the computed public key to 'pk'.
 */
void wots_pk_from_sig(const xmss_params *params, unsigned char *pk,
                      const unsigned char *sig, const unsigned char *msg,
                      const unsigned char *pub_seed, uint32_t addr[8])
{
    unsigned int *lengths = OQS_MEM_calloc(params->wots_len, sizeof(unsigned int ));
    const size_t thash_buf_len = 2 * params->padding_len + 4 * params->n + 32;
    unsigned char *thash_buf = OQS_MEM_malloc(thash_buf_len);
    unsigned int i;
    if (lengths == NULL || thash_buf == NULL) {
        return;
    }

    chain_lengths(params, lengths, msg);

    for (i = 0; i < params->wots_len; i++) {
        set_chain_addr(addr, i);
        gen_chain(params, pk + i*params->n, sig + i*params->n,
                  lengths[i], params->wots_w - 1 - lengths[i], pub_seed, addr, thash_buf);
    }

    OQS_MEM_insecure_free(lengths);
    OQS_MEM_insecure_free(thash_buf);
}