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Compute OPE cipher structure only when needed.

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The OPE cipher is tied to the current blinded key which is tied to the current
time period. Hence create the OPE cipher structure when we create a new
descriptor (and build its blinded key).
This commit is contained in:
George Kadianakis 2018-07-17 12:03:18 -04:00 committed by Nick Mathewson
parent f00b7a7faa
commit d8b71609cb
2 changed files with 40 additions and 26 deletions
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62
src/or/hs_service.c
View File

@ -1074,6 +1074,7 @@ service_descriptor_free_(hs_service_descriptor_t *desc)
SMARTLIST_FOREACH(desc->previous_hsdirs, char *, s, tor_free(s));
smartlist_free(desc->previous_hsdirs);
}
crypto_ope_free(desc->ope_cipher);
tor_free(desc);
}
@ -1378,13 +1379,30 @@ build_service_desc_plaintext(const hs_service_t *service,
return ret;
}
/** Compute the descriptor's OPE cipher for encrypting revision counters. */
static crypto_ope_t *
generate_ope_cipher_for_desc(const hs_service_descriptor_t *hs_desc)
{
/* Compute OPE key as H("rev-counter-generation" | blinded privkey) */
uint8_t key[DIGEST256_LEN];
crypto_digest_t *digest = crypto_digest256_new(DIGEST_SHA3_256);
const char ope_key_prefix[] = "rev-counter-generation";
const ed25519_secret_key_t *eph_privkey = &hs_desc->blinded_kp.seckey;
crypto_digest_add_bytes(digest, ope_key_prefix, sizeof(ope_key_prefix));
crypto_digest_add_bytes(digest, (char*)eph_privkey->seckey,
sizeof(eph_privkey->seckey));
crypto_digest_get_digest(digest, (char *)key, sizeof(key));
crypto_digest_free(digest);
return crypto_ope_new(key);
}
/* For the given service and descriptor object, create the key material which
* is the blinded keypair and the descriptor signing keypair. Return 0 on
* success else -1 on error where the generated keys MUST be ignored. */
static int
build_service_desc_keys(const hs_service_t *service,
hs_service_descriptor_t *desc,
uint64_t time_period_num)
hs_service_descriptor_t *desc)
{
int ret = 0;
ed25519_keypair_t kp;
@ -1400,10 +1418,17 @@ build_service_desc_keys(const hs_service_t *service,
memcpy(&kp.pubkey, &service->keys.identity_pk, sizeof(kp.pubkey));
memcpy(&kp.seckey, &service->keys.identity_sk, sizeof(kp.seckey));
/* Build blinded keypair for this time period. */
hs_build_blinded_keypair(&kp, NULL, 0, time_period_num, &desc->blinded_kp);
hs_build_blinded_keypair(&kp, NULL, 0, desc->time_period_num,
&desc->blinded_kp);
/* Let's not keep too much traces of our keys in memory. */
memwipe(&kp, 0, sizeof(kp));
/* Compute the OPE cipher struct (it's tied to the current blinded key) */
log_info(LD_GENERAL,
"Getting OPE for TP#%u", (unsigned) desc->time_period_num);
tor_assert_nonfatal(!desc->ope_cipher);
desc->ope_cipher = generate_ope_cipher_for_desc(desc);
/* No need for extra strong, this is a temporary key only for this
* descriptor. Nothing long term. */
if (ed25519_keypair_generate(&desc->signing_kp, 0) < 0) {
@ -1438,10 +1463,12 @@ build_service_descriptor(hs_service_t *service, time_t now,
tor_assert(desc_out);
desc = service_descriptor_new();
/* Set current time period */
desc->time_period_num = time_period_num;
/* Create the needed keys so we can setup the descriptor content. */
if (build_service_desc_keys(service, desc, time_period_num) < 0) {
if (build_service_desc_keys(service, desc) < 0) {
goto err;
}
/* Setup plaintext descriptor content. */
@ -2395,28 +2422,11 @@ set_descriptor_revision_counter(hs_service_descriptor_t *hs_desc, time_t now,
seconds_since_start_of_srv = OPE_INPUT_MAX;
}
/* Now we compute the actual revision counter value by encrypting the
plaintext using an OPE construction: */
/* First, compute OPE key as: K = H("rev-counter-generation" | S) */
uint8_t key[DIGEST256_LEN];
{
crypto_digest_t *digest = crypto_digest256_new(DIGEST_SHA3_256);
const char ope_key_prefix[] = "rev-counter-generation";
ed25519_secret_key_t *eph_privkey = &hs_desc->blinded_kp.seckey;
crypto_digest_add_bytes(digest, ope_key_prefix, sizeof(ope_key_prefix));
crypto_digest_add_bytes(digest, (char*)eph_privkey->seckey,
sizeof(eph_privkey->seckey));
crypto_digest_get_digest(digest, (char *)key, sizeof(key));
crypto_digest_free(digest);
}
{ /* Now encrypt the revision counter! */
crypto_ope_t *ope = NULL;
ope = crypto_ope_new(key);
rev_counter = crypto_ope_encrypt(ope, (int) seconds_since_start_of_srv);
crypto_ope_free(ope);
}
/* Now we compute the final revision counter value by encrypting the
plaintext using our OPE cipher: */
tor_assert(hs_desc->ope_cipher);
rev_counter = crypto_ope_encrypt(hs_desc->ope_cipher,
(int) seconds_since_start_of_srv);
/* The OPE module returns UINT64_MAX in case of errors. */
tor_assert_nonfatal(rev_counter < UINT64_MAX);

4
src/or/hs_service.h
View File

@ -131,6 +131,10 @@ typedef struct hs_service_descriptor_t {
* from this list, this means we received new dirinfo and we need to
* reupload our descriptor. */
smartlist_t *previous_hsdirs;
/** The OPE cipher for encrypting revision counters for this descriptor.
* Tied to the descriptor blinded key. */
crypto_ope_t *ope_cipher;
} hs_service_descriptor_t;
/* Service key material. */