1 /* Copyright (c) 2023, Google LLC
2 *
3 * Permission to use, copy, modify, and/or distribute this software for any
4 * purpose with or without fee is hereby granted, provided that the above
5 * copyright notice and this permission notice appear in all copies.
6 *
7 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
8 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
9 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
10 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
11 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
12 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
13 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
14
15 #include <openssl/base.h>
16
17 #include <string.h>
18
19 #include "./address.h"
20 #include "./fors.h"
21 #include "./params.h"
22 #include "./spx_util.h"
23 #include "./thash.h"
24
spx_fors_sk_gen(uint8_t * fors_sk,uint32_t idx,const uint8_t sk_seed[SPX_N],const uint8_t pk_seed[SPX_N],uint8_t addr[32])25 void spx_fors_sk_gen(uint8_t *fors_sk, uint32_t idx,
26 const uint8_t sk_seed[SPX_N], const uint8_t pk_seed[SPX_N],
27 uint8_t addr[32]) {
28 uint8_t sk_addr[32];
29 memcpy(sk_addr, addr, sizeof(sk_addr));
30
31 spx_set_type(sk_addr, SPX_ADDR_TYPE_FORSPRF);
32 spx_copy_keypair_addr(sk_addr, addr);
33 spx_set_tree_index(sk_addr, idx);
34 spx_thash_prf(fors_sk, pk_seed, sk_seed, sk_addr);
35 }
36
spx_fors_treehash(uint8_t root_node[SPX_N],const uint8_t sk_seed[SPX_N],uint32_t i,uint32_t z,const uint8_t pk_seed[SPX_N],uint8_t addr[32])37 void spx_fors_treehash(uint8_t root_node[SPX_N], const uint8_t sk_seed[SPX_N],
38 uint32_t i /*target node index*/,
39 uint32_t z /*target node height*/,
40 const uint8_t pk_seed[SPX_N], uint8_t addr[32]) {
41
42 BSSL_CHECK(z <= SPX_FORS_HEIGHT);
43 BSSL_CHECK(i < (uint32_t)(SPX_FORS_TREES * (1 << (SPX_FORS_HEIGHT - z))));
44
45 if (z == 0) {
46 uint8_t sk[SPX_N];
47 spx_set_tree_height(addr, 0);
48 spx_set_tree_index(addr, i);
49 spx_fors_sk_gen(sk, i, sk_seed, pk_seed, addr);
50 spx_thash_f(root_node, sk, pk_seed, addr);
51 } else {
52 // Stores left node and right node.
53 uint8_t nodes[2 * SPX_N];
54 spx_fors_treehash(nodes, sk_seed, 2 * i, z - 1, pk_seed, addr);
55 spx_fors_treehash(nodes + SPX_N, sk_seed, 2 * i + 1, z - 1, pk_seed, addr);
56 spx_set_tree_height(addr, z);
57 spx_set_tree_index(addr, i);
58 spx_thash_h(root_node, nodes, pk_seed, addr);
59 }
60 }
61
spx_fors_sign(uint8_t * fors_sig,const uint8_t message[SPX_FORS_MSG_BYTES],const uint8_t sk_seed[SPX_N],const uint8_t pk_seed[SPX_N],uint8_t addr[32])62 void spx_fors_sign(uint8_t *fors_sig, const uint8_t message[SPX_FORS_MSG_BYTES],
63 const uint8_t sk_seed[SPX_N], const uint8_t pk_seed[SPX_N],
64 uint8_t addr[32]) {
65 uint32_t indices[SPX_FORS_TREES];
66
67 // Derive FORS indices compatible with the NIST changes.
68 spx_base_b(indices, SPX_FORS_TREES, message, /*log2_b=*/SPX_FORS_HEIGHT);
69
70 for (size_t i = 0; i < SPX_FORS_TREES; ++i) {
71 spx_set_tree_height(addr, 0);
72 // Write the FORS secret key element to the correct position.
73 spx_fors_sk_gen(fors_sig + i * SPX_N * (SPX_FORS_HEIGHT + 1),
74 i * (1 << SPX_FORS_HEIGHT) + indices[i], sk_seed, pk_seed,
75 addr);
76 for (size_t j = 0; j < SPX_FORS_HEIGHT; ++j) {
77 size_t s = (indices[i] / (1 << j)) ^ 1;
78 // Write the FORS auth path element to the correct position.
79 spx_fors_treehash(fors_sig + SPX_N * (i * (SPX_FORS_HEIGHT + 1) + j + 1),
80 sk_seed, i * (1ULL << (SPX_FORS_HEIGHT - j)) + s, j,
81 pk_seed, addr);
82 }
83 }
84 }
85
spx_fors_pk_from_sig(uint8_t * fors_pk,const uint8_t fors_sig[SPX_FORS_BYTES],const uint8_t message[SPX_FORS_MSG_BYTES],const uint8_t pk_seed[SPX_N],uint8_t addr[32])86 void spx_fors_pk_from_sig(uint8_t *fors_pk,
87 const uint8_t fors_sig[SPX_FORS_BYTES],
88 const uint8_t message[SPX_FORS_MSG_BYTES],
89 const uint8_t pk_seed[SPX_N], uint8_t addr[32]) {
90 uint32_t indices[SPX_FORS_TREES];
91 uint8_t tmp[2 * SPX_N];
92 uint8_t roots[SPX_FORS_TREES * SPX_N];
93
94 // Derive FORS indices compatible with the NIST changes.
95 spx_base_b(indices, SPX_FORS_TREES, message, /*log2_b=*/SPX_FORS_HEIGHT);
96
97 for (size_t i = 0; i < SPX_FORS_TREES; ++i) {
98 // Pointer to current sk and authentication path
99 const uint8_t *sk = fors_sig + i * SPX_N * (SPX_FORS_HEIGHT + 1);
100 const uint8_t *auth = fors_sig + i * SPX_N * (SPX_FORS_HEIGHT + 1) + SPX_N;
101 uint8_t nodes[2 * SPX_N];
102
103 spx_set_tree_height(addr, 0);
104 spx_set_tree_index(addr, (i * (1 << SPX_FORS_HEIGHT)) + indices[i]);
105
106 spx_thash_f(nodes, sk, pk_seed, addr);
107
108 for (size_t j = 0; j < SPX_FORS_HEIGHT; ++j) {
109 spx_set_tree_height(addr, j + 1);
110
111 // Even node
112 if (((indices[i] / (1 << j)) % 2) == 0) {
113 spx_set_tree_index(addr, spx_get_tree_index(addr) / 2);
114 memcpy(tmp, nodes, SPX_N);
115 memcpy(tmp + SPX_N, auth + j * SPX_N, SPX_N);
116 spx_thash_h(nodes + SPX_N, tmp, pk_seed, addr);
117 } else {
118 spx_set_tree_index(addr, (spx_get_tree_index(addr) - 1) / 2);
119 memcpy(tmp, auth + j * SPX_N, SPX_N);
120 memcpy(tmp + SPX_N, nodes, SPX_N);
121 spx_thash_h(nodes + SPX_N, tmp, pk_seed, addr);
122 }
123 memcpy(nodes, nodes + SPX_N, SPX_N);
124 }
125 memcpy(roots + i * SPX_N, nodes, SPX_N);
126 }
127
128 uint8_t forspk_addr[32];
129 memcpy(forspk_addr, addr, sizeof(forspk_addr));
130 spx_set_type(forspk_addr, SPX_ADDR_TYPE_FORSPK);
131 spx_copy_keypair_addr(forspk_addr, addr);
132 spx_thash_tk(fors_pk, roots, pk_seed, forspk_addr);
133 }
134