diff options
Diffstat (limited to 'src/or/dirauth/shared_random.c')
| -rw-r--r-- | src/or/dirauth/shared_random.c | 1446 |
1 files changed, 1446 insertions, 0 deletions
diff --git a/src/or/dirauth/shared_random.c b/src/or/dirauth/shared_random.c new file mode 100644 index 0000000000..e9644adf9e --- /dev/null +++ b/src/or/dirauth/shared_random.c @@ -0,0 +1,1446 @@ +/* Copyright (c) 2016-2017, 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 "or.h" +#include "shared_random.h" +#include "config.h" +#include "confparse.h" +#include "networkstatus.h" +#include "routerkeys.h" +#include "router.h" +#include "routerlist.h" +#include "shared_random_state.h" +#include "util.h" + +#include "dirauth/dirvote.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 <b>orig</b>. */ +STATIC sr_srv_t * +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 <b>rsa_identity</b> + * 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 <b>commit</b>. */ +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 <b>commit</b> + * 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 !tor_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 <b>encoded</b> containing reveal information and + * store the information in-place in <b>commit</b>. 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 <b>commit</b>, 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 <b>commit</b> 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 (tor_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; +} + +/* Convert a given srv object to a string for the control port. This doesn't + * fail and the srv object MUST be valid. */ +static char * +srv_to_control_string(const sr_srv_t *srv) +{ + char *srv_str; + char srv_hash_encoded[SR_SRV_VALUE_BASE64_LEN + 1]; + tor_assert(srv); + + sr_srv_encode(srv_hash_encoded, sizeof(srv_hash_encoded), srv); + tor_asprintf(&srv_str, "%s", srv_hash_encoded); + return srv_str; +} + +/* Return a heap allocated string that contains the given <b>srv</b> string + * representation formatted for a networkstatus document using the + * <b>key</b> 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 + * <b>identity_digest</b>. 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 <b>commit</b> should be kept depending on + * the current phase and state of the protocol. The <b>voter_key</b> is the + * RSA identity key fingerprint of the authority's vote from which the + * commit comes from. The <b>phase</b> 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 <b>commit</b> 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 <b>commit</b> 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 <b>commit</b> to our persistent state. Depending on the current + * phase, different actions are taken. Steals reference of <b>commit</b>. + * 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 <b>n_agreements</b> 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 <b>sl</b> 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 <b>votes</b>, return the SRV object from them that has + * been voted by the majority of dirauths. If <b>current</b> 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; +} + +/* Encode the given shared random value and put it in dst. Destination + * buffer must be at least SR_SRV_VALUE_BASE64_LEN plus the NULL byte. */ +void +sr_srv_encode(char *dst, size_t dst_len, const sr_srv_t *srv) +{ + int ret; + /* Extra byte for the NULL terminated char. */ + char buf[SR_SRV_VALUE_BASE64_LEN + 1]; + + tor_assert(dst); + tor_assert(srv); + tor_assert(dst_len >= sizeof(buf)); + + ret = base64_encode(buf, sizeof(buf), (const char *) srv->value, + sizeof(srv->value), 0); + /* Always expect the full length without the NULL byte. */ + tor_assert(ret == (sizeof(buf) - 1)); + tor_assert(ret <= (int) dst_len); + strlcpy(dst, buf, dst_len); +} + +/* 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 + * <b>timestamp</b>. <b>my_rsa_cert</b> 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. */ + tor_assert(sr_state_get_phase() == SR_PHASE_REVEAL); + 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 list of arguments from a SRV value either from a vote, consensus + * or from our disk state and return a newly allocated srv object. NULL is + * returned on error. + * + * The arguments' order: + * num_reveals, value + */ +sr_srv_t * +sr_parse_srv(const smartlist_t *args) +{ + char *value; + int ok, ret; + uint64_t num_reveals; + sr_srv_t *srv = NULL; + + tor_assert(args); + + if (smartlist_len(args) < 2) { + goto end; + } + + /* First argument is the number of reveal values */ + num_reveals = tor_parse_uint64(smartlist_get(args, 0), + 10, 0, UINT64_MAX, &ok, NULL); + if (!ok) { + goto end; + } + /* Second and last argument is the shared random value it self. */ + value = smartlist_get(args, 1); + if (strlen(value) != SR_SRV_VALUE_BASE64_LEN) { + goto end; + } + + srv = tor_malloc_zero(sizeof(*srv)); + srv->num_reveals = num_reveals; + /* We subtract one byte from the srclen because the function ignores the + * '=' character in the given buffer. This is broken but it's a documented + * behavior of the implementation. */ + ret = base64_decode((char *) srv->value, sizeof(srv->value), value, + SR_SRV_VALUE_BASE64_LEN - 1); + if (ret != sizeof(srv->value)) { + tor_free(srv); + srv = NULL; + goto end; + } + end: + return srv; +} + +/* 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 <b>args</b> 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 <b>voter_key</b> that might + * contain some useful <b>commits</b>. 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 or_options_t *options = 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. + * + * <b>num_srv_agreements</b> 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 or_options_t *options = 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 <b>consensus</b>. 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(srv_dup(consensus->sr_info.previous_srv)); + sr_state_set_current_srv(srv_dup(consensus->sr_info.current_srv)); + } + + /* Prepare our state so that it's ready for the next voting period. */ + sr_state_update(dirvote_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(); +} + +/* Return the current SRV string representation for the control port. Return a + * newly allocated string on success containing the value else "" if not found + * or if we don't have a valid consensus yet. */ +char * +sr_get_current_for_control(void) +{ + char *srv_str; + const networkstatus_t *c = networkstatus_get_latest_consensus(); + if (c && c->sr_info.current_srv) { + srv_str = srv_to_control_string(c->sr_info.current_srv); + } else { + srv_str = tor_strdup(""); + } + return srv_str; +} + +/* Return the previous SRV string representation for the control port. Return + * a newly allocated string on success containing the value else "" if not + * found or if we don't have a valid consensus yet. */ +char * +sr_get_previous_for_control(void) +{ + char *srv_str; + const networkstatus_t *c = networkstatus_get_latest_consensus(); + if (c && c->sr_info.previous_srv) { + srv_str = srv_to_control_string(c->sr_info.previous_srv); + } else { + srv_str = tor_strdup(""); + } + return srv_str; +} + +/* Return current shared random value from the latest consensus. Caller can + * NOT keep a reference to the returned pointer. Return NULL if none. */ +const sr_srv_t * +sr_get_current(const networkstatus_t *ns) +{ + const networkstatus_t *consensus; + + /* Use provided ns else get a live one */ + if (ns) { + consensus = ns; + } else { + consensus = networkstatus_get_live_consensus(approx_time()); + } + /* Ideally we would never be asked for an SRV without a live consensus. Make + * sure this assumption is correct. */ + tor_assert_nonfatal(consensus); + + if (consensus) { + return consensus->sr_info.current_srv; + } + return NULL; +} + +/* Return previous shared random value from the latest consensus. Caller can + * NOT keep a reference to the returned pointer. Return NULL if none. */ +const sr_srv_t * +sr_get_previous(const networkstatus_t *ns) +{ + const networkstatus_t *consensus; + + /* Use provided ns else get a live one */ + if (ns) { + consensus = ns; + } else { + consensus = networkstatus_get_live_consensus(approx_time()); + } + /* Ideally we would never be asked for an SRV without a live consensus. Make + * sure this assumption is correct. */ + tor_assert_nonfatal(consensus); + + if (consensus) { + return consensus->sr_info.previous_srv; + } + return NULL; +} + +#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) */ + |