static void bds_round()

in xmss_fast.c [446:515]

• 62 lines of code
• 12 McCabe index (conditional complexity)

static void bds_round(bds_state *state, const unsigned long leaf_idx, const unsigned char *sk_seed, const xmss_params *params, unsigned char *pub_seed, uint32_t addr[8])
{
  unsigned int i;
  unsigned int n = params->n;
  unsigned int h = params->h;
  unsigned int k = params->k;

  unsigned int tau = h;
  unsigned int startidx;
  unsigned int offset, rowidx;
  unsigned char buf[2 * n];

  uint32_t ots_addr[8];
  uint32_t ltree_addr[8];
  uint32_t  node_addr[8];
  // only copy layer and tree address parts
  memcpy(ots_addr, addr, 12);
  // type = ots
  setType(ots_addr, 0);
  memcpy(ltree_addr, addr, 12);
  setType(ltree_addr, 1);
  memcpy(node_addr, addr, 12);
  setType(node_addr, 2);

  for (i = 0; i < h; i++) {
    if (! ((leaf_idx >> i) & 1)) {
      tau = i;
      break;
    }
  }

  if (tau > 0) {
    memcpy(buf,     state->auth + (tau-1) * n, n);
    // we need to do this before refreshing state->keep to prevent overwriting
    memcpy(buf + n, state->keep + ((tau-1) >> 1) * n, n);
  }
  if (!((leaf_idx >> (tau + 1)) & 1) && (tau < h - 1)) {
    memcpy(state->keep + (tau >> 1)*n, state->auth + tau*n, n);
  }
  if (tau == 0) {
    setLtreeADRS(ltree_addr, leaf_idx);
    setOTSADRS(ots_addr, leaf_idx);
    gen_leaf_wots(state->auth, sk_seed, params, pub_seed, ltree_addr, ots_addr);
  }
  else {
    setTreeHeight(node_addr, (tau-1));
    setTreeIndex(node_addr, leaf_idx >> tau);
    hash_h(state->auth + tau * n, buf, pub_seed, node_addr, n);
    for (i = 0; i < tau; i++) {
      if (i < h - k) {
        memcpy(state->auth + i * n, state->treehash[i].node, n);
      }
      else {
        offset = (1 << (h - 1 - i)) + i - h;
        rowidx = ((leaf_idx >> i) - 1) >> 1;
        memcpy(state->auth + i * n, state->retain + (offset + rowidx) * n, n);
      }
    }

    for (i = 0; i < ((tau < h - k) ? tau : (h - k)); i++) {
      startidx = leaf_idx + 1 + 3 * (1 << i);
      if (startidx < 1U << h) {
        state->treehash[i].h = i;
        state->treehash[i].next_idx = startidx;
        state->treehash[i].completed = 0;
        state->treehash[i].stackusage = 0;
      }
    }
  }
}