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Improved key generation

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In the public comments to draft version of NIST Special Publication 800-208, ETSI TC CYBER WG QSC identified a multi-target attack against the method of pseudorandom key generation used in this referrence implementation. ETSI TC CYBER WG QSC suggested using the pseudorandom key generation method from SPHINCS+, however, there is still a multi-user attack against that key generation method.

This commit revises the pseudorandom key generation method by using the method from SPINCS+, but adding SEED as an input in order to protect against multi-user attacks. Since prf() only accepts 32-byte inputs, the new key generation method uses a new PRF. The resulting key generation method is sk[i] = prf_keygen(sk_seed, pub_seed || adrs).
This commit is contained in:
David Cooper 2020-04-28 10:02:06 -04:00
vanhempi 2237b6f4f0
commit 3e28db2362
7 muutettua tiedostoa jossa 40 lisäystä ja 59 poistoa
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18
hash.c
Näytä tiedosto

@ -12,6 +12,7 @@
#define XMSS_HASH_PADDING_H 1
#define XMSS_HASH_PADDING_HASH 2
#define XMSS_HASH_PADDING_PRF 3
#define XMSS_HASH_PADDING_PRF_KEYGEN 4
void addr_to_bytes(unsigned char *bytes, const uint32_t addr[8])
{
@ -59,6 +60,23 @@ int prf(const xmss_params *params,
return core_hash(params, out, buf, params->padding_len + params->n + 32);
}
/*
* Computes PRF_keygen(key, in), for a key of params->n bytes, and an input
* of 32 + params->n bytes
*/
int prf_keygen(const xmss_params *params,
unsigned char *out, const unsigned char *in,
const unsigned char *key)
{
unsigned char buf[params->padding_len + 2*params->n + 32];
ull_to_bytes(buf, params->padding_len, XMSS_HASH_PADDING_PRF_KEYGEN);
memcpy(buf + params->padding_len, key, params->n);
memcpy(buf + params->padding_len + params->n, in, params->n + 32);
return core_hash(params, out, buf, params->padding_len + 2*params->n + 32);
}
/*
* Computes the message hash using R, the public root, the index of the leaf
* node, and the message. Notably, it requires m_with_prefix to have 4*n bytes

4
hash.h
Näytä tiedosto

@ -10,6 +10,10 @@ int prf(const xmss_params *params,
unsigned char *out, const unsigned char in[32],
const unsigned char *key);
int prf_keygen(const xmss_params *params,
unsigned char *out, const unsigned char *in,
const unsigned char *key);
int h_msg(const xmss_params *params,
unsigned char *out,
const unsigned char *in, unsigned long long inlen,

19
wots.c
Näytä tiedosto

@ -9,17 +9,22 @@
/**
* Helper method for pseudorandom key generation.
* Expands an n-byte array into a len*n byte array using the `prf` function.
* 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)
unsigned char *outseeds, const unsigned char *inseed,
const unsigned char *pub_seed, uint32_t addr[8])
{
uint32_t i;
unsigned char ctr[32];
unsigned char 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++) {
ull_to_bytes(ctr, 32, i);
prf(params, outseeds + i*params->n, ctr, inseed);
set_chain_addr(addr, i);
addr_to_bytes(buf + params->n, addr);
prf_keygen(params, outseeds + i*params->n, buf, inseed);
}
}
@ -116,7 +121,7 @@ void wots_pkgen(const xmss_params *params,
uint32_t i;
/* The WOTS+ private key is derived from the seed. */
expand_seed(params, pk, seed);
expand_seed(params, pk, seed, pub_seed, addr);
for (i = 0; i < params->wots_len; i++) {
set_chain_addr(addr, i);
@ -140,7 +145,7 @@ void wots_sign(const xmss_params *params,
chain_lengths(params, lengths, msg);
/* The WOTS+ private key is derived from the seed. */
expand_seed(params, sig, seed);
expand_seed(params, sig, seed, pub_seed, addr);
for (i = 0; i < params->wots_len; i++) {
set_chain_addr(addr, i);

24
xmss_commons.c
Näytä tiedosto

@ -105,35 +105,13 @@ void gen_leaf_wots(const xmss_params *params, unsigned char *leaf,
const unsigned char *sk_seed, const unsigned char *pub_seed,
uint32_t ltree_addr[8], uint32_t ots_addr[8])
{
unsigned char seed[params->n];
unsigned char pk[params->wots_sig_bytes];
get_seed(params, seed, sk_seed, ots_addr);
wots_pkgen(params, pk, seed, pub_seed, ots_addr);
wots_pkgen(params, pk, sk_seed, pub_seed, ots_addr);
l_tree(params, leaf, pk, pub_seed, ltree_addr);
}
/**
* Used for pseudo-random key generation.
* Generates the seed for the WOTS key pair at address 'addr'.
*
* Takes n-byte sk_seed and returns n-byte seed using 32 byte address 'addr'.
*/
void get_seed(const xmss_params *params, unsigned char *seed,
const unsigned char *sk_seed, uint32_t addr[8])
{
unsigned char bytes[32];
/* Make sure that chain addr, hash addr, and key bit are zeroed. */
set_chain_addr(addr, 0);
set_hash_addr(addr, 0);
set_key_and_mask(addr, 0);
/* Generate seed. */
addr_to_bytes(bytes, addr);
prf(params, seed, bytes, sk_seed);
}
/**
* Verifies a given message signature pair under a given public key.

9
xmss_commons.h
Näytä tiedosto

@ -13,15 +13,6 @@ void gen_leaf_wots(const xmss_params *params, unsigned char *leaf,
const unsigned char *sk_seed, const unsigned char *pub_seed,
uint32_t ltree_addr[8], uint32_t ots_addr[8]);
/**
* Used for pseudo-random key generation.
* Generates the seed for the WOTS key pair at address 'addr'.
*
* Takes n-byte sk_seed and returns n-byte seed using 32 byte address 'addr'.
*/
void get_seed(const xmss_params *params, unsigned char *seed,
const unsigned char *sk_seed, uint32_t addr[8]);
/**
* Verifies a given message signature pair under a given public key.
* Note that this assumes a pk without an OID, i.e. [root || PUB_SEED]

6
xmss_core.c
Näytä tiedosto

@ -174,7 +174,6 @@ int xmssmt_core_sign(const xmss_params *params,
unsigned char root[params->n];
unsigned char *mhash = root;
unsigned char ots_seed[params->n];
unsigned long long idx;
unsigned char idx_bytes_32[32];
unsigned int i;
@ -217,13 +216,10 @@ int xmssmt_core_sign(const xmss_params *params,
set_tree_addr(ots_addr, idx);
set_ots_addr(ots_addr, idx_leaf);
/* Get a seed for the WOTS keypair. */
get_seed(params, ots_seed, sk_seed, ots_addr);
/* Compute a WOTS signature. */
/* Initially, root = mhash, but on subsequent iterations it is the root
of the subtree below the currently processed subtree. */
wots_sign(params, sm, root, ots_seed, pub_seed, ots_addr);
wots_sign(params, sm, root, sk_seed, pub_seed, ots_addr);
sm += params->wots_sig_bytes;
/* Compute the authentication path for the used WOTS leaf. */

19
xmss_core_fast.c
Näytä tiedosto

@ -623,7 +623,6 @@ int xmss_core_sign(const xmss_params *params,
// Init working params
unsigned char R[params->n];
unsigned char msg_h[params->n];
unsigned char ots_seed[params->n];
uint32_t ots_addr[8] = {0};
// ---------------------------------
@ -670,11 +669,8 @@ int xmss_core_sign(const xmss_params *params,
set_type(ots_addr, 0);
set_ots_addr(ots_addr, idx);
// Compute seed for OTS key pair
get_seed(params, ots_seed, sk_seed, ots_addr);
// Compute WOTS signature
wots_sign(params, sm, msg_h, ots_seed, pub_seed, ots_addr);
wots_sign(params, sm, msg_h, sk_seed, pub_seed, ots_addr);
sm += params->wots_sig_bytes;
*smlen += params->wots_sig_bytes;
@ -707,7 +703,6 @@ int xmss_core_sign(const xmss_params *params,
int xmssmt_core_keypair(const xmss_params *params,
unsigned char *pk, unsigned char *sk)
{
unsigned char ots_seed[params->n];
uint32_t addr[8] = {0};
unsigned int i;
unsigned char *wots_sigs;
@ -745,8 +740,7 @@ int xmssmt_core_keypair(const xmss_params *params,
// Compute seed for OTS key pair
treehash_init(params, pk, params->tree_height, 0, states + i, sk+params->index_bytes, pk+params->n, addr);
set_layer_addr(addr, (i+1));
get_seed(params, ots_seed, sk + params->index_bytes, addr);
wots_sign(params, wots_sigs + i*params->wots_sig_bytes, pk, ots_seed, pk+params->n, addr);
wots_sign(params, wots_sigs + i*params->wots_sig_bytes, pk, sk + params->index_bytes, pk+params->n, addr);
}
// Address now points to the single tree on layer d-1
treehash_init(params, pk, params->tree_height, 0, states + i, sk+params->index_bytes, pk+params->n, addr);
@ -783,7 +777,6 @@ int xmssmt_core_sign(const xmss_params *params,
// Init working params
unsigned char R[params->n];
unsigned char msg_h[params->n];
unsigned char ots_seed[params->n];
uint32_t addr[8] = {0};
uint32_t ots_addr[8] = {0};
unsigned char idx_bytes_32[32];
@ -867,11 +860,8 @@ int xmssmt_core_sign(const xmss_params *params,
set_tree_addr(ots_addr, idx_tree);
set_ots_addr(ots_addr, idx_leaf);
// Compute seed for OTS key pair
get_seed(params, ots_seed, sk_seed, ots_addr);
// Compute WOTS signature
wots_sign(params, sm, msg_h, ots_seed, pub_seed, ots_addr);
wots_sign(params, sm, msg_h, sk_seed, pub_seed, ots_addr);
sm += params->wots_sig_bytes;
*smlen += params->wots_sig_bytes;
@ -929,8 +919,7 @@ int xmssmt_core_sign(const xmss_params *params,
set_tree_addr(ots_addr, ((idx + 1) >> ((i+2) * params->tree_height)));
set_ots_addr(ots_addr, (((idx >> ((i+1) * params->tree_height)) + 1) & ((1 << params->tree_height)-1)));
get_seed(params, ots_seed, sk+params->index_bytes, ots_addr);
wots_sign(params, wots_sigs + i*params->wots_sig_bytes, states[i].stack, ots_seed, pub_seed, ots_addr);
wots_sign(params, wots_sigs + i*params->wots_sig_bytes, states[i].stack, sk_seed, pub_seed, ots_addr);
states[params->d + i].stackoffset = 0;
states[params->d + i].next_leaf = 0;