/* Copyright (c) 2016-2020, The Tor Project, Inc. */
/* See LICENSE for licensing information */
/**
* \file shared_random.c
*
* \brief Functions and data structure needed to accomplish the shared
* random protocol as defined in proposal #250.
*
* \details
*
* This file implements the dirauth-only commit-and-reveal protocol specified
* by proposal #250. The protocol has two phases (sr_phase_t): the commitment
* phase and the reveal phase (see get_sr_protocol_phase()).
*
* During the protocol, directory authorities keep state in memory (using
* sr_state_t) and in disk (using sr_disk_state_t). The synchronization between
* these two data structures happens in disk_state_update() and
* disk_state_parse().
*
* Here is a rough protocol outline:
*
* 1) In the beginning of the commitment phase, dirauths generate a
* commitment/reveal value for the current protocol run (see
* new_protocol_run() and sr_generate_our_commit()).
*
* 2) During voting, dirauths publish their commits in their votes
* depending on the current phase. Dirauths also include the two
* latest shared random values (SRV) in their votes.
* (see sr_get_string_for_vote())
*
* 3) Upon receiving a commit from a vote, authorities parse it, verify
* it, and attempt to save any new commitment or reveal information in
* their state file (see extract_shared_random_commits() and
* sr_handle_received_commits()). They also parse SRVs from votes to
* decide which SRV should be included in the final consensus (see
* extract_shared_random_srvs()).
*
* 3) After voting is done, we count the SRVs we extracted from the votes,
* to find the one voted by the majority of dirauths which should be
* included in the final consensus (see get_majority_srv_from_votes()).
* If an appropriate SRV is found, it is embedded in the consensus (see
* sr_get_string_for_consensus()).
*
* 4) At the end of the reveal phase, dirauths compute a fresh SRV for the
* day using the active commits (see sr_compute_srv()). This new SRV
* is embedded in the votes as described above.
*
* Some more notes:
*
* - To support rebooting authorities and to avoid double voting, each dirauth
* saves the current state of the protocol on disk so that it can resume
* normally in case of reboot. The disk state (sr_disk_state_t) is managed by
* shared_random_state.c:state_query() and we go to extra lengths to ensure
* that the state is flushed on disk everytime we receive any useful
* information like commits or SRVs.
*
* - When we receive a commit from a vote, we examine it to see if it's useful
* to us and whether it's appropriate to receive it according to the current
* phase of the protocol (see should_keep_commit()). If the commit is useful
* to us, we save it in our disk state using save_commit_to_state(). When we
* receive the reveal information corresponding to a commitment, we verify
* that they indeed match using verify_commit_and_reveal().
*
* - We treat consensuses as the ground truth, so everytime we generate a new
* consensus we update our SR state accordingly even if our local view was
* different (see sr_act_post_consensus()).
*
* - After a consensus has been composed, the SR protocol state gets prepared
* for the next voting session using sr_state_update(). That function takes
* care of housekeeping and also rotates the SRVs and commits in case a new
* protocol run is coming up. We also call sr_state_update() on bootup (in
* sr_state_init()), to prepare the state for the very first voting session.
*
* Terminology:
*
* - "Commitment" is the commitment value of the commit-and-reveal protocol.
*
* - "Reveal" is the reveal value of the commit-and-reveal protocol.
*
* - "Commit" is a struct (sr_commit_t) that contains a commitment value and
* optionally also a corresponding reveal value.
*
* - "SRV" is the Shared Random Value that gets generated as the result of the
* commit-and-reveal protocol.
**/
#define SHARED_RANDOM_PRIVATE
#include "core/or/or.h"
#include "feature/dirauth/shared_random.h"
#include "app/config/config.h"
#include "lib/confmgt/confmgt.h"
#include "lib/crypt_ops/crypto_rand.h"
#include "lib/crypt_ops/crypto_util.h"
#include "feature/nodelist/networkstatus.h"
#include "feature/relay/router.h"
#include "feature/relay/routerkeys.h"
#include "feature/nodelist/dirlist.h"
#include "feature/hs_common/shared_random_client.h"
#include "feature/dirauth/shared_random_state.h"
#include "feature/dirauth/voting_schedule.h"
#include "feature/dirauth/dirvote.h"
#include "feature/dirauth/authmode.h"
#include "feature/dirauth/dirauth_sys.h"
#include "feature/dirauth/dirauth_options_st.h"
#include "feature/nodelist/authority_cert_st.h"
#include "feature/nodelist/networkstatus_st.h"
/** String prefix of shared random values in votes/consensuses. */
static const char previous_srv_str[] = "shared-rand-previous-value";
static const char current_srv_str[] = "shared-rand-current-value";
static const char commit_ns_str[] = "shared-rand-commit";
static const char sr_flag_ns_str[] = "shared-rand-participate";
/** The value of the consensus param AuthDirNumSRVAgreements found in the
* vote. This is set once the consensus creation subsystem requests the
* SRV(s) that should be put in the consensus. We use this value to decide
* if we keep or not an SRV. */
static int32_t num_srv_agreements_from_vote;
/** Return a heap allocated copy of the SRV orig. */
sr_srv_t *
sr_srv_dup(const sr_srv_t *orig)
{
sr_srv_t *duplicate = NULL;
if (!orig) {
return NULL;
}
duplicate = tor_malloc_zero(sizeof(sr_srv_t));
duplicate->num_reveals = orig->num_reveals;
memcpy(duplicate->value, orig->value, sizeof(duplicate->value));
return duplicate;
}
/** Allocate a new commit object and initializing it with rsa_identity
* that MUST be provided. The digest algorithm is set to the default one
* that is supported. The rest is uninitialized. This never returns NULL. */
static sr_commit_t *
commit_new(const char *rsa_identity)
{
sr_commit_t *commit;
tor_assert(rsa_identity);
commit = tor_malloc_zero(sizeof(*commit));
commit->alg = SR_DIGEST_ALG;
memcpy(commit->rsa_identity, rsa_identity, sizeof(commit->rsa_identity));
base16_encode(commit->rsa_identity_hex, sizeof(commit->rsa_identity_hex),
commit->rsa_identity, sizeof(commit->rsa_identity));
return commit;
}
/** Issue a log message describing commit. */
static void
commit_log(const sr_commit_t *commit)
{
tor_assert(commit);
log_debug(LD_DIR, "SR: Commit from %s", sr_commit_get_rsa_fpr(commit));
log_debug(LD_DIR, "SR: Commit: [TS: %" PRIu64 "] [Encoded: %s]",
commit->commit_ts, commit->encoded_commit);
log_debug(LD_DIR, "SR: Reveal: [TS: %" PRIu64 "] [Encoded: %s]",
commit->reveal_ts, safe_str(commit->encoded_reveal));
}
/** Make sure that the commitment and reveal information in commit
* match. If they match return 0, return -1 otherwise. This function MUST be
* used everytime we receive a new reveal value. Furthermore, the commit
* object MUST have a reveal value and the hash of the reveal value. */
STATIC int
verify_commit_and_reveal(const sr_commit_t *commit)
{
tor_assert(commit);
log_debug(LD_DIR, "SR: Validating commit from authority %s",
sr_commit_get_rsa_fpr(commit));
/* Check that the timestamps match. */
if (commit->commit_ts != commit->reveal_ts) {
log_warn(LD_BUG, "SR: Commit timestamp %" PRIu64 " doesn't match reveal "
"timestamp %" PRIu64, commit->commit_ts,
commit->reveal_ts);
goto invalid;
}
/* Verify that the hashed_reveal received in the COMMIT message, matches
* the reveal we just received. */
{
/* We first hash the reveal we just received. */
char received_hashed_reveal[sizeof(commit->hashed_reveal)];
/* Only sha3-256 is supported. */
if (commit->alg != SR_DIGEST_ALG) {
goto invalid;
}
/* Use the invariant length since the encoded reveal variable has an
* extra byte for the NUL terminated byte. */
if (crypto_digest256(received_hashed_reveal, commit->encoded_reveal,
SR_REVEAL_BASE64_LEN, commit->alg) < 0) {
/* Unable to digest the reveal blob, this is unlikely. */
goto invalid;
}
/* Now compare that with the hashed_reveal we received in COMMIT. */
if (fast_memneq(received_hashed_reveal, commit->hashed_reveal,
sizeof(received_hashed_reveal))) {
log_warn(LD_BUG, "SR: Received reveal value from authority %s "
"doesn't match the commit value.",
sr_commit_get_rsa_fpr(commit));
goto invalid;
}
}
return 0;
invalid:
return -1;
}
/** Return true iff the commit contains an encoded reveal value. */
STATIC int
commit_has_reveal_value(const sr_commit_t *commit)
{
return !fast_mem_is_zero(commit->encoded_reveal,
sizeof(commit->encoded_reveal));
}
/** Parse the encoded commit. The format is:
* base64-encode( TIMESTAMP || H(REVEAL) )
*
* If successfully decoded and parsed, commit is updated and 0 is returned.
* On error, return -1. */
STATIC int
commit_decode(const char *encoded, sr_commit_t *commit)
{
int decoded_len = 0;
size_t offset = 0;
char b64_decoded[SR_COMMIT_LEN];
tor_assert(encoded);
tor_assert(commit);
if (strlen(encoded) > SR_COMMIT_BASE64_LEN) {
/* This means that if we base64 decode successfully the reveiced commit,
* we'll end up with a bigger decoded commit thus unusable. */
goto error;
}
/* Decode our encoded commit. Let's be careful here since _encoded_ is
* coming from the network in a dirauth vote so we expect nothing more
* than the base64 encoded length of a commit. */
decoded_len = base64_decode(b64_decoded, sizeof(b64_decoded),
encoded, strlen(encoded));
if (decoded_len < 0) {
log_warn(LD_BUG, "SR: Commit from authority %s can't be decoded.",
sr_commit_get_rsa_fpr(commit));
goto error;
}
if (decoded_len != SR_COMMIT_LEN) {
log_warn(LD_BUG, "SR: Commit from authority %s decoded length doesn't "
"match the expected length (%d vs %u).",
sr_commit_get_rsa_fpr(commit), decoded_len,
(unsigned)SR_COMMIT_LEN);
goto error;
}
/* First is the timestamp (8 bytes). */
commit->commit_ts = tor_ntohll(get_uint64(b64_decoded));
offset += sizeof(uint64_t);
/* Next is hashed reveal. */
memcpy(commit->hashed_reveal, b64_decoded + offset,
sizeof(commit->hashed_reveal));
/* Copy the base64 blob to the commit. Useful for voting. */
strlcpy(commit->encoded_commit, encoded, sizeof(commit->encoded_commit));
return 0;
error:
return -1;
}
/** Parse the b64 blob at encoded containing reveal information and
* store the information in-place in commit. Return 0 on success else
* a negative value. */
STATIC int
reveal_decode(const char *encoded, sr_commit_t *commit)
{
int decoded_len = 0;
char b64_decoded[SR_REVEAL_LEN];
tor_assert(encoded);
tor_assert(commit);
if (strlen(encoded) > SR_REVEAL_BASE64_LEN) {
/* This means that if we base64 decode successfully the received reveal
* value, we'll end up with a bigger decoded value thus unusable. */
goto error;
}
/* Decode our encoded reveal. Let's be careful here since _encoded_ is
* coming from the network in a dirauth vote so we expect nothing more
* than the base64 encoded length of our reveal. */
decoded_len = base64_decode(b64_decoded, sizeof(b64_decoded),
encoded, strlen(encoded));
if (decoded_len < 0) {
log_warn(LD_BUG, "SR: Reveal from authority %s can't be decoded.",
sr_commit_get_rsa_fpr(commit));
goto error;
}
if (decoded_len != SR_REVEAL_LEN) {
log_warn(LD_BUG, "SR: Reveal from authority %s decoded length is "
"doesn't match the expected length (%d vs %u)",
sr_commit_get_rsa_fpr(commit), decoded_len,
(unsigned)SR_REVEAL_LEN);
goto error;
}
commit->reveal_ts = tor_ntohll(get_uint64(b64_decoded));
/* Copy the last part, the random value. */
memcpy(commit->random_number, b64_decoded + 8,
sizeof(commit->random_number));
/* Also copy the whole message to use during verification */
strlcpy(commit->encoded_reveal, encoded, sizeof(commit->encoded_reveal));
return 0;
error:
return -1;
}
/** Encode a reveal element using a given commit object to dst which is a
* buffer large enough to put the base64-encoded reveal construction. The
* format is as follow:
* REVEAL = base64-encode( TIMESTAMP || H(RN) )
* Return base64 encoded length on success else a negative value.
*/
STATIC int
reveal_encode(const sr_commit_t *commit, char *dst, size_t len)
{
int ret;
size_t offset = 0;
char buf[SR_REVEAL_LEN] = {0};
tor_assert(commit);
tor_assert(dst);
set_uint64(buf, tor_htonll(commit->reveal_ts));
offset += sizeof(uint64_t);
memcpy(buf + offset, commit->random_number,
sizeof(commit->random_number));
/* Let's clean the buffer and then b64 encode it. */
memset(dst, 0, len);
ret = base64_encode(dst, len, buf, sizeof(buf), 0);
/* Wipe this buffer because it contains our random value. */
memwipe(buf, 0, sizeof(buf));
return ret;
}
/** Encode the given commit object to dst which is a buffer large enough to
* put the base64-encoded commit. The format is as follow:
* COMMIT = base64-encode( TIMESTAMP || H(H(RN)) )
* Return base64 encoded length on success else a negative value.
*/
STATIC int
commit_encode(const sr_commit_t *commit, char *dst, size_t len)
{
size_t offset = 0;
char buf[SR_COMMIT_LEN] = {0};
tor_assert(commit);
tor_assert(dst);
/* First is the timestamp (8 bytes). */
set_uint64(buf, tor_htonll(commit->commit_ts));
offset += sizeof(uint64_t);
/* and then the hashed reveal. */
memcpy(buf + offset, commit->hashed_reveal,
sizeof(commit->hashed_reveal));
/* Clean the buffer and then b64 encode it. */
memset(dst, 0, len);
return base64_encode(dst, len, buf, sizeof(buf), 0);
}
/** Cleanup both our global state and disk state. */
static void
sr_cleanup(void)
{
sr_state_free_all();
}
/** Using commit, return a newly allocated string containing the commit
* information that should be used during SRV calculation. It's the caller
* responsibility to free the memory. Return NULL if this is not a commit to be
* used for SRV calculation. */
static char *
get_srv_element_from_commit(const sr_commit_t *commit)
{
char *element;
tor_assert(commit);
if (!commit_has_reveal_value(commit)) {
return NULL;
}
tor_asprintf(&element, "%s%s", sr_commit_get_rsa_fpr(commit),
commit->encoded_reveal);
return element;
}
/** Return a srv object that is built with the construction:
* SRV = SHA3-256("shared-random" | INT_8(reveal_num) |
* INT_4(version) | HASHED_REVEALS | previous_SRV)
* This function cannot fail. */
static sr_srv_t *
generate_srv(const char *hashed_reveals, uint64_t reveal_num,
const sr_srv_t *previous_srv)
{
char msg[DIGEST256_LEN + SR_SRV_MSG_LEN] = {0};
size_t offset = 0;
sr_srv_t *srv;
tor_assert(hashed_reveals);
/* Add the invariant token. */
memcpy(msg, SR_SRV_TOKEN, SR_SRV_TOKEN_LEN);
offset += SR_SRV_TOKEN_LEN;
set_uint64(msg + offset, tor_htonll(reveal_num));
offset += sizeof(uint64_t);
set_uint32(msg + offset, htonl(SR_PROTO_VERSION));
offset += sizeof(uint32_t);
memcpy(msg + offset, hashed_reveals, DIGEST256_LEN);
offset += DIGEST256_LEN;
if (previous_srv != NULL) {
memcpy(msg + offset, previous_srv->value, sizeof(previous_srv->value));
}
/* Ok we have our message and key for the HMAC computation, allocate our
* srv object and do the last step. */
srv = tor_malloc_zero(sizeof(*srv));
crypto_digest256((char *) srv->value, msg, sizeof(msg), SR_DIGEST_ALG);
srv->num_reveals = reveal_num;
{
/* Debugging. */
char srv_hash_encoded[SR_SRV_VALUE_BASE64_LEN + 1];
sr_srv_encode(srv_hash_encoded, sizeof(srv_hash_encoded), srv);
log_info(LD_DIR, "SR: Generated SRV: %s", srv_hash_encoded);
}
return srv;
}
/** Compare reveal values and return the result. This should exclusively be
* used by smartlist_sort(). */
static int
compare_reveal_(const void **_a, const void **_b)
{
const sr_commit_t *a = *_a, *b = *_b;
return fast_memcmp(a->hashed_reveal, b->hashed_reveal,
sizeof(a->hashed_reveal));
}
/** Given commit give the line that we should place in our votes.
* It's the responsibility of the caller to free the string. */
static char *
get_vote_line_from_commit(const sr_commit_t *commit, sr_phase_t phase)
{
char *vote_line = NULL;
switch (phase) {
case SR_PHASE_COMMIT:
tor_asprintf(&vote_line, "%s %u %s %s %s\n",
commit_ns_str,
SR_PROTO_VERSION,
crypto_digest_algorithm_get_name(commit->alg),
sr_commit_get_rsa_fpr(commit),
commit->encoded_commit);
break;
case SR_PHASE_REVEAL:
{
/* Send a reveal value for this commit if we have one. */
const char *reveal_str = commit->encoded_reveal;
if (fast_mem_is_zero(commit->encoded_reveal,
sizeof(commit->encoded_reveal))) {
reveal_str = "";
}
tor_asprintf(&vote_line, "%s %u %s %s %s %s\n",
commit_ns_str,
SR_PROTO_VERSION,
crypto_digest_algorithm_get_name(commit->alg),
sr_commit_get_rsa_fpr(commit),
commit->encoded_commit, reveal_str);
break;
}
default:
tor_assert(0);
}
log_debug(LD_DIR, "SR: Commit vote line: %s", vote_line);
return vote_line;
}
/** Return a heap allocated string that contains the given srv string
* representation formatted for a networkstatus document using the
* key as the start of the line. This doesn't return NULL. */
static char *
srv_to_ns_string(const sr_srv_t *srv, const char *key)
{
char *srv_str;
char srv_hash_encoded[SR_SRV_VALUE_BASE64_LEN + 1];
tor_assert(srv);
tor_assert(key);
sr_srv_encode(srv_hash_encoded, sizeof(srv_hash_encoded), srv);
tor_asprintf(&srv_str, "%s %" PRIu64 " %s\n", key,
srv->num_reveals, srv_hash_encoded);
log_debug(LD_DIR, "SR: Consensus SRV line: %s", srv_str);
return srv_str;
}
/** Given the previous SRV and the current SRV, return a heap allocated
* string with their data that could be put in a vote or a consensus. Caller
* must free the returned string. Return NULL if no SRVs were provided. */
static char *
get_ns_str_from_sr_values(const sr_srv_t *prev_srv, const sr_srv_t *cur_srv)
{
smartlist_t *chunks = NULL;
char *srv_str;
if (!prev_srv && !cur_srv) {
return NULL;
}
chunks = smartlist_new();
if (prev_srv) {
char *srv_line = srv_to_ns_string(prev_srv, previous_srv_str);
smartlist_add(chunks, srv_line);
}
if (cur_srv) {
char *srv_line = srv_to_ns_string(cur_srv, current_srv_str);
smartlist_add(chunks, srv_line);
}
/* Join the line(s) here in one string to return. */
srv_str = smartlist_join_strings(chunks, "", 0, NULL);
SMARTLIST_FOREACH(chunks, char *, s, tor_free(s));
smartlist_free(chunks);
return srv_str;
}
/** Return 1 iff the two commits have the same commitment values. This
* function does not care about reveal values. */
STATIC int
commitments_are_the_same(const sr_commit_t *commit_one,
const sr_commit_t *commit_two)
{
tor_assert(commit_one);
tor_assert(commit_two);
if (strcmp(commit_one->encoded_commit, commit_two->encoded_commit)) {
return 0;
}
return 1;
}
/** We just received a commit from the vote of authority with
* identity_digest. Return 1 if this commit is authorititative that
* is, it belongs to the authority that voted it. Else return 0 if not. */
STATIC int
commit_is_authoritative(const sr_commit_t *commit,
const char *voter_key)
{
tor_assert(commit);
tor_assert(voter_key);
return fast_memeq(commit->rsa_identity, voter_key,
sizeof(commit->rsa_identity));
}
/** Decide if the newly received commit should be kept depending on
* the current phase and state of the protocol. The voter_key is the
* RSA identity key fingerprint of the authority's vote from which the
* commit comes from. The phase is the phase we should be validating
* the commit for. Return 1 if the commit should be added to our state or 0
* if not. */
STATIC int
should_keep_commit(const sr_commit_t *commit, const char *voter_key,
sr_phase_t phase)
{
const sr_commit_t *saved_commit;
tor_assert(commit);
tor_assert(voter_key);
log_debug(LD_DIR, "SR: Inspecting commit from %s (voter: %s)?",
sr_commit_get_rsa_fpr(commit),
hex_str(voter_key, DIGEST_LEN));
/* For a commit to be considered, it needs to be authoritative (it should
* be the voter's own commit). */
if (!commit_is_authoritative(commit, voter_key)) {
log_debug(LD_DIR, "SR: Ignoring non-authoritative commit.");
goto ignore;
}
/* Let's make sure, for extra safety, that this fingerprint is known to
* us. Even though this comes from a vote, doesn't hurt to be
* extracareful. */
if (trusteddirserver_get_by_v3_auth_digest(commit->rsa_identity) == NULL) {
log_warn(LD_DIR, "SR: Fingerprint %s is not from a recognized "
"authority. Discarding commit.",
escaped(commit->rsa_identity));
goto ignore;
}
/* Check if the authority that voted for commit has already posted
* a commit before. */
saved_commit = sr_state_get_commit(commit->rsa_identity);
switch (phase) {
case SR_PHASE_COMMIT:
/* Already having a commit for an authority so ignore this one. */
if (saved_commit) {
/* Receiving known commits should happen naturally since commit phase
lasts multiple rounds. However if the commitment value changes
during commit phase, it might be a bug so log more loudly. */
if (!commitments_are_the_same(commit, saved_commit)) {
log_info(LD_DIR,
"SR: Received altered commit from %s in commit phase.",
sr_commit_get_rsa_fpr(commit));
} else {
log_debug(LD_DIR, "SR: Ignoring known commit during commit phase.");
}
goto ignore;
}
/* A commit with a reveal value during commitment phase is very wrong. */
if (commit_has_reveal_value(commit)) {
log_warn(LD_DIR, "SR: Commit from authority %s has a reveal value "
"during COMMIT phase. (voter: %s)",
sr_commit_get_rsa_fpr(commit),
hex_str(voter_key, DIGEST_LEN));
goto ignore;
}
break;
case SR_PHASE_REVEAL:
/* We are now in reveal phase. We keep a commit if and only if:
*
* - We have already seen a commit by this auth, AND
* - the saved commit has the same commitment value as this one, AND
* - the saved commit has no reveal information, AND
* - this commit does have reveal information, AND
* - the reveal & commit information are matching.
*
* If all the above are true, then we are interested in this new commit
* for its reveal information. */
if (!saved_commit) {
log_debug(LD_DIR, "SR: Ignoring commit first seen in reveal phase.");
goto ignore;
}
if (!commitments_are_the_same(commit, saved_commit)) {
log_warn(LD_DIR, "SR: Commit from authority %s is different from "
"previous commit in our state (voter: %s)",
sr_commit_get_rsa_fpr(commit),
hex_str(voter_key, DIGEST_LEN));
goto ignore;
}
if (commit_has_reveal_value(saved_commit)) {
log_debug(LD_DIR, "SR: Ignoring commit with known reveal info.");
goto ignore;
}
if (!commit_has_reveal_value(commit)) {
log_debug(LD_DIR, "SR: Ignoring commit without reveal value.");
goto ignore;
}
if (verify_commit_and_reveal(commit) < 0) {
log_warn(LD_BUG, "SR: Commit from authority %s has an invalid "
"reveal value. (voter: %s)",
sr_commit_get_rsa_fpr(commit),
hex_str(voter_key, DIGEST_LEN));
goto ignore;
}
break;
default:
tor_assert(0);
}
return 1;
ignore:
return 0;
}
/** We are in reveal phase and we found a valid and verified commit in
* a vote that contains reveal values that we could use. Update the commit
* we have in our state. Never call this with an unverified commit. */
STATIC void
save_commit_during_reveal_phase(const sr_commit_t *commit)
{
sr_commit_t *saved_commit;
tor_assert(commit);
/* Get the commit from our state. */
saved_commit = sr_state_get_commit(commit->rsa_identity);
tor_assert(saved_commit);
/* Safety net. They can not be different commitments at this point. */
int same_commits = commitments_are_the_same(commit, saved_commit);
tor_assert(same_commits);
/* Copy reveal information to our saved commit. */
sr_state_copy_reveal_info(saved_commit, commit);
}
/** Save commit to our persistent state. Depending on the current
* phase, different actions are taken. Steals reference of commit.
* The commit object MUST be valid and verified before adding it to the
* state. */
STATIC void
save_commit_to_state(sr_commit_t *commit)
{
sr_phase_t phase = sr_state_get_phase();
ASSERT_COMMIT_VALID(commit);
switch (phase) {
case SR_PHASE_COMMIT:
/* During commit phase, just save any new authoritative commit */
sr_state_add_commit(commit);
break;
case SR_PHASE_REVEAL:
save_commit_during_reveal_phase(commit);
sr_commit_free(commit);
break;
default:
tor_assert(0);
}
}
/** Return 1 if we should we keep an SRV voted by n_agreements auths.
* Return 0 if we should ignore it. */
static int
should_keep_srv(int n_agreements)
{
/* Check if the most popular SRV has reached majority. */
int n_voters = get_n_authorities(V3_DIRINFO);
int votes_required_for_majority = (n_voters / 2) + 1;
/* We need at the very least majority to keep a value. */
if (n_agreements < votes_required_for_majority) {
log_notice(LD_DIR, "SR: SRV didn't reach majority [%d/%d]!",
n_agreements, votes_required_for_majority);
return 0;
}
/* When we just computed a new SRV, we need to have super majority in order
* to keep it. */
if (sr_state_srv_is_fresh()) {
/* Check if we have super majority for this new SRV value. */
if (n_agreements < num_srv_agreements_from_vote) {
log_notice(LD_DIR, "SR: New SRV didn't reach agreement [%d/%d]!",
n_agreements, num_srv_agreements_from_vote);
return 0;
}
}
return 1;
}
/** Helper: compare two DIGEST256_LEN digests. */
static int
compare_srvs_(const void **_a, const void **_b)
{
const sr_srv_t *a = *_a, *b = *_b;
return tor_memcmp(a->value, b->value, sizeof(a->value));
}
/** Return the most frequent member of the sorted list of DIGEST256_LEN
* digests in sl with the count of that most frequent element. */
static sr_srv_t *
smartlist_get_most_frequent_srv(const smartlist_t *sl, int *count_out)
{
return smartlist_get_most_frequent_(sl, compare_srvs_, count_out);
}
/** Compare two SRVs. Used in smartlist sorting. */
static int
compare_srv_(const void **_a, const void **_b)
{
const sr_srv_t *a = *_a, *b = *_b;
return fast_memcmp(a->value, b->value,
sizeof(a->value));
}
/** Using a list of votes, return the SRV object from them that has
* been voted by the majority of dirauths. If current is set, we look
* for the current SRV value else the previous one. The returned pointer is
* an object located inside a vote. NULL is returned if no appropriate value
* could be found. */
STATIC sr_srv_t *
get_majority_srv_from_votes(const smartlist_t *votes, int current)
{
int count = 0;
sr_srv_t *most_frequent_srv = NULL;
sr_srv_t *the_srv = NULL;
smartlist_t *srv_list;
tor_assert(votes);
srv_list = smartlist_new();
/* Walk over votes and register any SRVs found. */
SMARTLIST_FOREACH_BEGIN(votes, networkstatus_t *, v) {
sr_srv_t *srv_tmp = NULL;
if (!v->sr_info.participate) {
/* Ignore vote that do not participate. */
continue;
}
/* Do we want previous or current SRV? */
srv_tmp = current ? v->sr_info.current_srv : v->sr_info.previous_srv;
if (!srv_tmp) {
continue;
}
smartlist_add(srv_list, srv_tmp);
} SMARTLIST_FOREACH_END(v);
smartlist_sort(srv_list, compare_srv_);
most_frequent_srv = smartlist_get_most_frequent_srv(srv_list, &count);
if (!most_frequent_srv) {
goto end;
}
/* Was this SRV voted by enough auths for us to keep it? */
if (!should_keep_srv(count)) {
goto end;
}
/* We found an SRV that we can use! Habemus SRV! */
the_srv = most_frequent_srv;
{
/* Debugging */
char encoded[SR_SRV_VALUE_BASE64_LEN + 1];
sr_srv_encode(encoded, sizeof(encoded), the_srv);
log_debug(LD_DIR, "SR: Chosen SRV by majority: %s (%d votes)", encoded,
count);
}
end:
/* We do not free any sr_srv_t values, we don't have the ownership. */
smartlist_free(srv_list);
return the_srv;
}
/** Free a commit object. */
void
sr_commit_free_(sr_commit_t *commit)
{
if (commit == NULL) {
return;
}
/* Make sure we do not leave OUR random number in memory. */
memwipe(commit->random_number, 0, sizeof(commit->random_number));
tor_free(commit);
}
/** Generate the commitment/reveal value for the protocol run starting at
* timestamp. my_rsa_cert is our authority RSA certificate. */
sr_commit_t *
sr_generate_our_commit(time_t timestamp, const authority_cert_t *my_rsa_cert)
{
sr_commit_t *commit = NULL;
char digest[DIGEST_LEN];
tor_assert(my_rsa_cert);
/* Get our RSA identity fingerprint */
if (crypto_pk_get_digest(my_rsa_cert->identity_key, digest) < 0) {
goto error;
}
/* New commit with our identity key. */
commit = commit_new(digest);
/* Generate the reveal random value */
crypto_strongest_rand(commit->random_number,
sizeof(commit->random_number));
commit->commit_ts = commit->reveal_ts = timestamp;
/* Now get the base64 blob that corresponds to our reveal */
if (reveal_encode(commit, commit->encoded_reveal,
sizeof(commit->encoded_reveal)) < 0) {
log_err(LD_DIR, "SR: Unable to encode our reveal value!");
goto error;
}
/* Now let's create the commitment */
tor_assert(commit->alg == SR_DIGEST_ALG);
/* The invariant length is used here since the encoded reveal variable
* has an extra byte added for the NULL terminated byte. */
if (crypto_digest256(commit->hashed_reveal, commit->encoded_reveal,
SR_REVEAL_BASE64_LEN, commit->alg) < 0) {
goto error;
}
/* Now get the base64 blob that corresponds to our commit. */
if (commit_encode(commit, commit->encoded_commit,
sizeof(commit->encoded_commit)) < 0) {
log_err(LD_DIR, "SR: Unable to encode our commit value!");
goto error;
}
log_debug(LD_DIR, "SR: Generated our commitment:");
commit_log(commit);
/* Our commit better be valid :). */
commit->valid = 1;
return commit;
error:
sr_commit_free(commit);
return NULL;
}
/** Compute the shared random value based on the active commits in our
* state. */
void
sr_compute_srv(void)
{
uint64_t reveal_num = 0;
char *reveals = NULL;
smartlist_t *chunks, *commits;
digestmap_t *state_commits;
/* Computing a shared random value in the commit phase is very wrong. This
* should only happen at the very end of the reveal phase when a new
* protocol run is about to start. */
if (BUG(sr_state_get_phase() != SR_PHASE_REVEAL))
return;
state_commits = sr_state_get_commits();
commits = smartlist_new();
chunks = smartlist_new();
/* We must make a list of commit ordered by authority fingerprint in
* ascending order as specified by proposal 250. */
DIGESTMAP_FOREACH(state_commits, key, sr_commit_t *, c) {
/* Extra safety net, make sure we have valid commit before using it. */
ASSERT_COMMIT_VALID(c);
/* Let's not use a commit from an authority that we don't know. It's
* possible that an authority could be removed during a protocol run so
* that commit value should never be used in the SRV computation. */
if (trusteddirserver_get_by_v3_auth_digest(c->rsa_identity) == NULL) {
log_warn(LD_DIR, "SR: Fingerprint %s is not from a recognized "
"authority. Discarding commit for the SRV computation.",
sr_commit_get_rsa_fpr(c));
continue;
}
/* We consider this commit valid. */
smartlist_add(commits, c);
} DIGESTMAP_FOREACH_END;
smartlist_sort(commits, compare_reveal_);
/* Now for each commit for that sorted list in ascending order, we'll
* build the element for each authority that needs to go into the srv
* computation. */
SMARTLIST_FOREACH_BEGIN(commits, const sr_commit_t *, c) {
char *element = get_srv_element_from_commit(c);
if (element) {
smartlist_add(chunks, element);
reveal_num++;
}
} SMARTLIST_FOREACH_END(c);
smartlist_free(commits);
{
/* Join all reveal values into one giant string that we'll hash so we
* can generated our shared random value. */
sr_srv_t *current_srv;
char hashed_reveals[DIGEST256_LEN];
reveals = smartlist_join_strings(chunks, "", 0, NULL);
SMARTLIST_FOREACH(chunks, char *, s, tor_free(s));
smartlist_free(chunks);
if (crypto_digest256(hashed_reveals, reveals, strlen(reveals),
SR_DIGEST_ALG) < 0) {
goto end;
}
current_srv = generate_srv(hashed_reveals, reveal_num,
sr_state_get_previous_srv());
sr_state_set_current_srv(current_srv);
/* We have a fresh SRV, flag our state. */
sr_state_set_fresh_srv();
}
end:
tor_free(reveals);
}
/** Parse a commit from a vote or from our disk state and return a newly
* allocated commit object. NULL is returned on error.
*
* The commit's data is in args and the order matters very much:
* version, algname, RSA fingerprint, commit value[, reveal value]
*/
sr_commit_t *
sr_parse_commit(const smartlist_t *args)
{
uint32_t version;
char *value, digest[DIGEST_LEN];
digest_algorithm_t alg;
const char *rsa_identity_fpr;
sr_commit_t *commit = NULL;
if (smartlist_len(args) < 4) {
goto error;
}
/* First is the version number of the SR protocol which indicates at which
* version that commit was created. */
value = smartlist_get(args, 0);
version = (uint32_t) tor_parse_ulong(value, 10, 1, UINT32_MAX, NULL, NULL);
if (version > SR_PROTO_VERSION) {
log_info(LD_DIR, "SR: Commit version %" PRIu32 " (%s) is not supported.",
version, escaped(value));
goto error;
}
/* Second is the algorithm. */
value = smartlist_get(args, 1);
alg = crypto_digest_algorithm_parse_name(value);
if (alg != SR_DIGEST_ALG) {
log_warn(LD_BUG, "SR: Commit algorithm %s is not recognized.",
escaped(value));
goto error;
}
/* Third argument is the RSA fingerprint of the auth and turn it into a
* digest value. */
rsa_identity_fpr = smartlist_get(args, 2);
if (base16_decode(digest, DIGEST_LEN, rsa_identity_fpr,
HEX_DIGEST_LEN) < 0) {
log_warn(LD_DIR, "SR: RSA fingerprint %s not decodable",
escaped(rsa_identity_fpr));
goto error;
}
/* Allocate commit since we have a valid identity now. */
commit = commit_new(digest);
/* Fourth argument is the commitment value base64-encoded. */
value = smartlist_get(args, 3);
if (commit_decode(value, commit) < 0) {
goto error;
}
/* (Optional) Fifth argument is the revealed value. */
if (smartlist_len(args) > 4) {
value = smartlist_get(args, 4);
if (reveal_decode(value, commit) < 0) {
goto error;
}
}
return commit;
error:
sr_commit_free(commit);
return NULL;
}
/** Called when we are done parsing a vote by voter_key that might
* contain some useful commits. Find if any of them should be kept
* and update our state accordingly. Once done, the list of commitments will
* be empty. */
void
sr_handle_received_commits(smartlist_t *commits, crypto_pk_t *voter_key)
{
char rsa_identity[DIGEST_LEN];
tor_assert(voter_key);
/* It's possible that the vote has _NO_ commits. */
if (commits == NULL) {
return;
}
/* Get the RSA identity fingerprint of this voter */
if (crypto_pk_get_digest(voter_key, rsa_identity) < 0) {
return;
}
SMARTLIST_FOREACH_BEGIN(commits, sr_commit_t *, commit) {
/* We won't need the commit in this list anymore, kept or not. */
SMARTLIST_DEL_CURRENT(commits, commit);
/* Check if this commit is valid and should be stored in our state. */
if (!should_keep_commit(commit, rsa_identity,
sr_state_get_phase())) {
sr_commit_free(commit);
continue;
}
/* Ok, we have a valid commit now that we are about to put in our state.
* so flag it valid from now on. */
commit->valid = 1;
/* Everything lines up: save this commit to state then! */
save_commit_to_state(commit);
} SMARTLIST_FOREACH_END(commit);
}
/** Return a heap-allocated string containing commits that should be put in
* the votes. It's the responsibility of the caller to free the string.
* This always return a valid string, either empty or with line(s). */
char *
sr_get_string_for_vote(void)
{
char *vote_str = NULL;
digestmap_t *state_commits;
smartlist_t *chunks = smartlist_new();
const dirauth_options_t *options = dirauth_get_options();
/* Are we participating in the protocol? */
if (!options->AuthDirSharedRandomness) {
goto end;
}
log_debug(LD_DIR, "SR: Preparing our vote info:");
/* First line, put in the vote the participation flag. */
{
char *sr_flag_line;
tor_asprintf(&sr_flag_line, "%s\n", sr_flag_ns_str);
smartlist_add(chunks, sr_flag_line);
}
/* In our vote we include every commitment in our permanent state. */
state_commits = sr_state_get_commits();
smartlist_t *state_commit_vote_lines = smartlist_new();
DIGESTMAP_FOREACH(state_commits, key, const sr_commit_t *, commit) {
char *line = get_vote_line_from_commit(commit, sr_state_get_phase());
smartlist_add(state_commit_vote_lines, line);
} DIGESTMAP_FOREACH_END;
/* Sort the commit strings by version (string, not numeric), algorithm,
* and fingerprint. This makes sure the commit lines in votes are in a
* recognisable, stable order. */
smartlist_sort_strings(state_commit_vote_lines);
/* Now add the sorted list of commits to the vote */
smartlist_add_all(chunks, state_commit_vote_lines);
smartlist_free(state_commit_vote_lines);
/* Add the SRV value(s) if any. */
{
char *srv_lines = get_ns_str_from_sr_values(sr_state_get_previous_srv(),
sr_state_get_current_srv());
if (srv_lines) {
smartlist_add(chunks, srv_lines);
}
}
end:
vote_str = smartlist_join_strings(chunks, "", 0, NULL);
SMARTLIST_FOREACH(chunks, char *, s, tor_free(s));
smartlist_free(chunks);
return vote_str;
}
/** Return a heap-allocated string that should be put in the consensus and
* contains the shared randomness values. It's the responsibility of the
* caller to free the string. NULL is returned if no SRV(s) available.
*
* This is called when a consensus (any flavor) is bring created thus it
* should NEVER change the state nor the state should be changed in between
* consensus creation.
*
* num_srv_agreements is taken from the votes thus the voted value
* that should be used.
* */
char *
sr_get_string_for_consensus(const smartlist_t *votes,
int32_t num_srv_agreements)
{
char *srv_str;
const dirauth_options_t *options = dirauth_get_options();
tor_assert(votes);
/* Not participating, avoid returning anything. */
if (!options->AuthDirSharedRandomness) {
log_info(LD_DIR, "SR: Support disabled (AuthDirSharedRandomness %d)",
options->AuthDirSharedRandomness);
goto end;
}
/* Set the global value of AuthDirNumSRVAgreements found in the votes. */
num_srv_agreements_from_vote = num_srv_agreements;
/* Check the votes and figure out if SRVs should be included in the final
* consensus. */
sr_srv_t *prev_srv = get_majority_srv_from_votes(votes, 0);
sr_srv_t *cur_srv = get_majority_srv_from_votes(votes, 1);
srv_str = get_ns_str_from_sr_values(prev_srv, cur_srv);
if (!srv_str) {
goto end;
}
return srv_str;
end:
return NULL;
}
/** We just computed a new consensus. Update our state with the SRVs
* from the consensus (might be NULL as well). Register the SRVs in our SR
* state and prepare for the upcoming protocol round. */
void
sr_act_post_consensus(const networkstatus_t *consensus)
{
const or_options_t *options = get_options();
/* Don't act if our state hasn't been initialized. We can be called during
* boot time when loading consensus from disk which is prior to the
* initialization of the SR subsystem. We also should not be doing
* anything if we are _not_ a directory authority and if we are a bridge
* authority. */
if (!sr_state_is_initialized() || !authdir_mode_v3(options) ||
authdir_mode_bridge(options)) {
return;
}
/* Set the majority voted SRVs in our state even if both are NULL. It
* doesn't matter this is what the majority has decided. Obviously, we can
* only do that if we have a consensus. */
if (consensus) {
/* Start by freeing the current SRVs since the SRVs we believed during
* voting do not really matter. Now that all the votes are in, we use the
* majority's opinion on which are the active SRVs. */
sr_state_clean_srvs();
/* Reset the fresh flag of the SRV so we know that from now on we don't
* have a new SRV to vote for. We just used the one from the consensus
* decided by the majority. */
sr_state_unset_fresh_srv();
/* Set the SR values from the given consensus. */
sr_state_set_previous_srv(sr_srv_dup(consensus->sr_info.previous_srv));
sr_state_set_current_srv(sr_srv_dup(consensus->sr_info.current_srv));
}
/* Prepare our state so that it's ready for the next voting period. */
sr_state_update(dirauth_sched_get_next_valid_after_time());
}
/** Initialize shared random subsystem. This MUST be called early in the boot
* process of tor. Return 0 on success else -1 on error. */
int
sr_init(int save_to_disk)
{
return sr_state_init(save_to_disk, 1);
}
/** Save our state to disk and cleanup everything. */
void
sr_save_and_cleanup(void)
{
sr_state_save();
sr_cleanup();
}
#ifdef TOR_UNIT_TESTS
/** Set the global value of number of SRV agreements so the test can play
* along by calling specific functions that don't parse the votes prior for
* the AuthDirNumSRVAgreements value. */
void
set_num_srv_agreements(int32_t value)
{
num_srv_agreements_from_vote = value;
}
#endif /* defined(TOR_UNIT_TESTS) */