diff options
Diffstat (limited to 'src/or/torcert.c')
| -rw-r--r-- | src/or/torcert.c | 410 |
1 files changed, 402 insertions, 8 deletions
diff --git a/src/or/torcert.c b/src/or/torcert.c index a6a33c675a..c58f3da2d3 100644 --- a/src/or/torcert.c +++ b/src/or/torcert.c @@ -6,8 +6,27 @@ * * \brief Implementation for ed25519-signed certificates as used in the Tor * protocol. + * + * This certificate format is designed to be simple and compact; it's + * documented in tor-spec.txt in the torspec.git repository. All of the + * certificates in this format are signed with an Ed25519 key; the + * contents themselves may be another Ed25519 key, a digest of a + * RSA key, or some other material. + * + * In this module there is also support for a crooss-certification of + * Ed25519 identities using (older) RSA1024 identities. + * + * Tor uses other types of certificate too, beyond those described in this + * module. Notably, our use of TLS requires us to touch X.509 certificates, + * even though sensible people would stay away from those. Our X.509 + * certificates are represented with tor_x509_cert_t, and implemented in + * tortls.c. We also have a separate certificate type that authorities + * use to authenticate their RSA signing keys with their RSA identity keys: + * that one is authority_cert_t, and it's mostly handled in routerlist.c. */ +#include "or.h" +#include "config.h" #include "crypto.h" #include "torcert.h" #include "ed25519_cert.h" @@ -137,7 +156,12 @@ tor_cert_parse(const uint8_t *encoded, const size_t len) cert->encoded_len = len; memcpy(cert->signed_key.pubkey, parsed->certified_key, 32); - cert->valid_until = parsed->exp_field * 3600; + int64_t valid_until_64 = ((int64_t)parsed->exp_field) * 3600; +#if SIZEOF_TIME_T < SIZEOF_INT64_T + if (valid_until_64 > TIME_MAX) + valid_until_64 = TIME_MAX - 1; +#endif + cert->valid_until = (time_t) valid_until_64; cert->cert_type = parsed->cert_type; for (unsigned i = 0; i < ed25519_cert_getlen_ext(parsed); ++i) { @@ -164,11 +188,17 @@ tor_cert_parse(const uint8_t *encoded, const size_t len) } /** Fill in <b>checkable_out</b> with the information needed to check - * the signature on <b>cert</b> with <b>pubkey</b>. */ + * the signature on <b>cert</b> with <b>pubkey</b>. + * + * On success, if <b>expiration_out</b> is provided, and it is some time + * _after_ the expiration time of this certificate, set it to the + * expiration time of this certificate. + */ int tor_cert_get_checkable_sig(ed25519_checkable_t *checkable_out, const tor_cert_t *cert, - const ed25519_public_key_t *pubkey) + const ed25519_public_key_t *pubkey, + time_t *expiration_out) { if (! pubkey) { if (cert->signing_key_included) @@ -185,6 +215,10 @@ tor_cert_get_checkable_sig(ed25519_checkable_t *checkable_out, memcpy(checkable_out->signature.sig, cert->encoded + signed_len, ED25519_SIG_LEN); + if (expiration_out) { + *expiration_out = MIN(*expiration_out, cert->valid_until); + } + return 0; } @@ -199,14 +233,15 @@ tor_cert_checksig(tor_cert_t *cert, { ed25519_checkable_t checkable; int okay; + time_t expires = TIME_MAX; - if (now && now > cert->valid_until) { - cert->cert_expired = 1; + if (tor_cert_get_checkable_sig(&checkable, cert, pubkey, &expires) < 0) return -1; - } - if (tor_cert_get_checkable_sig(&checkable, cert, pubkey) < 0) + if (now && now > expires) { + cert->cert_expired = 1; return -1; + } if (ed25519_checksig_batch(&okay, &checkable, 1) < 0) { cert->sig_bad = 1; @@ -255,6 +290,8 @@ tor_cert_opt_eq(const tor_cert_t *cert1, const tor_cert_t *cert2) return tor_cert_eq(cert1, cert2); } +#define RSA_ED_CROSSCERT_PREFIX "Tor TLS RSA/Ed25519 cross-certificate" + /** Create new cross-certification object to certify <b>ed_key</b> as the * master ed25519 identity key for the RSA identity key <b>rsa_key</b>. * Allocates and stores the encoded certificate in *<b>cert</b>, and returns @@ -279,11 +316,21 @@ tor_make_rsa_ed25519_crosscert(const ed25519_public_key_t *ed_key, ssize_t sz = rsa_ed_crosscert_encode(res, alloc_sz, cc); tor_assert(sz > 0 && sz <= alloc_sz); + crypto_digest_t *d = crypto_digest256_new(DIGEST_SHA256); + crypto_digest_add_bytes(d, RSA_ED_CROSSCERT_PREFIX, + strlen(RSA_ED_CROSSCERT_PREFIX)); + const int signed_part_len = 32 + 4; + crypto_digest_add_bytes(d, (char*)res, signed_part_len); + + uint8_t digest[DIGEST256_LEN]; + crypto_digest_get_digest(d, (char*)digest, sizeof(digest)); + crypto_digest_free(d); + int siglen = crypto_pk_private_sign(rsa_key, (char*)rsa_ed_crosscert_getarray_sig(cc), rsa_ed_crosscert_getlen_sig(cc), - (char*)res, signed_part_len); + (char*)digest, sizeof(digest)); tor_assert(siglen > 0 && siglen <= (int)crypto_pk_keysize(rsa_key)); tor_assert(siglen <= UINT8_MAX); cc->sig_len = siglen; @@ -295,3 +342,350 @@ tor_make_rsa_ed25519_crosscert(const ed25519_public_key_t *ed_key, return sz; } +/** + * Check whether the <b>crosscert_len</b> byte certificate in <b>crosscert</b> + * is in fact a correct cross-certification of <b>master_key</b> using + * the RSA key <b>rsa_id_key</b>. + * + * Also reject the certificate if it expired before + * <b>reject_if_expired_before</b>. + * + * Return 0 on success, negative on failure. + */ +int +rsa_ed25519_crosscert_check(const uint8_t *crosscert, + const size_t crosscert_len, + const crypto_pk_t *rsa_id_key, + const ed25519_public_key_t *master_key, + const time_t reject_if_expired_before) +{ + rsa_ed_crosscert_t *cc = NULL; + int rv; + +#define ERR(code, s) \ + do { \ + log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL, \ + "Received a bad RSA->Ed25519 crosscert: %s", \ + (s)); \ + rv = (code); \ + goto err; \ + } while (0) + + if (BUG(crypto_pk_keysize(rsa_id_key) > PK_BYTES)) + return -1; + + if (BUG(!crosscert)) + return -1; + + ssize_t parsed_len = rsa_ed_crosscert_parse(&cc, crosscert, crosscert_len); + if (parsed_len < 0 || crosscert_len != (size_t)parsed_len) { + ERR(-2, "Unparseable or overlong crosscert"); + } + + if (tor_memneq(rsa_ed_crosscert_getarray_ed_key(cc), + master_key->pubkey, + ED25519_PUBKEY_LEN)) { + ERR(-3, "Crosscert did not match Ed25519 key"); + } + + const uint32_t expiration_date = rsa_ed_crosscert_get_expiration(cc); + const uint64_t expiration_time = expiration_date * 3600; + + if (reject_if_expired_before < 0 || + expiration_time < (uint64_t)reject_if_expired_before) { + ERR(-4, "Crosscert is expired"); + } + + const uint8_t *eos = rsa_ed_crosscert_get_end_of_signed(cc); + const uint8_t *sig = rsa_ed_crosscert_getarray_sig(cc); + const uint8_t siglen = rsa_ed_crosscert_get_sig_len(cc); + tor_assert(eos >= crosscert); + tor_assert((size_t)(eos - crosscert) <= crosscert_len); + tor_assert(siglen == rsa_ed_crosscert_getlen_sig(cc)); + + /* Compute the digest */ + uint8_t digest[DIGEST256_LEN]; + crypto_digest_t *d = crypto_digest256_new(DIGEST_SHA256); + crypto_digest_add_bytes(d, RSA_ED_CROSSCERT_PREFIX, + strlen(RSA_ED_CROSSCERT_PREFIX)); + crypto_digest_add_bytes(d, (char*)crosscert, eos-crosscert); + crypto_digest_get_digest(d, (char*)digest, sizeof(digest)); + crypto_digest_free(d); + + /* Now check the signature */ + uint8_t signed_[PK_BYTES]; + int signed_len = crypto_pk_public_checksig(rsa_id_key, + (char*)signed_, sizeof(signed_), + (char*)sig, siglen); + if (signed_len < DIGEST256_LEN) { + ERR(-5, "Bad signature, or length of signed data not as expected"); + } + + if (tor_memneq(digest, signed_, DIGEST256_LEN)) { + ERR(-6, "The signature was good, but it didn't match the data"); + } + + rv = 0; + err: + rsa_ed_crosscert_free(cc); + return rv; +} + +/** Construct and return a new empty or_handshake_certs object */ +or_handshake_certs_t * +or_handshake_certs_new(void) +{ + return tor_malloc_zero(sizeof(or_handshake_certs_t)); +} + +/** Release all storage held in <b>certs</b> */ +void +or_handshake_certs_free(or_handshake_certs_t *certs) +{ + if (!certs) + return; + + tor_x509_cert_free(certs->auth_cert); + tor_x509_cert_free(certs->link_cert); + tor_x509_cert_free(certs->id_cert); + + tor_cert_free(certs->ed_id_sign); + tor_cert_free(certs->ed_sign_link); + tor_cert_free(certs->ed_sign_auth); + tor_free(certs->ed_rsa_crosscert); + + memwipe(certs, 0xBD, sizeof(*certs)); + tor_free(certs); +} + +#undef ERR +#define ERR(s) \ + do { \ + log_fn(severity, LD_PROTOCOL, \ + "Received a bad CERTS cell: %s", \ + (s)); \ + return 0; \ + } while (0) + +int +or_handshake_certs_rsa_ok(int severity, + or_handshake_certs_t *certs, + tor_tls_t *tls, + time_t now) +{ + tor_x509_cert_t *link_cert = certs->link_cert; + tor_x509_cert_t *auth_cert = certs->auth_cert; + tor_x509_cert_t *id_cert = certs->id_cert; + + if (certs->started_here) { + if (! (id_cert && link_cert)) + ERR("The certs we wanted (ID, Link) were missing"); + if (! tor_tls_cert_matches_key(tls, link_cert)) + ERR("The link certificate didn't match the TLS public key"); + if (! tor_tls_cert_is_valid(severity, link_cert, id_cert, now, 0)) + ERR("The link certificate was not valid"); + if (! tor_tls_cert_is_valid(severity, id_cert, id_cert, now, 1)) + ERR("The ID certificate was not valid"); + } else { + if (! (id_cert && auth_cert)) + ERR("The certs we wanted (ID, Auth) were missing"); + if (! tor_tls_cert_is_valid(LOG_PROTOCOL_WARN, auth_cert, id_cert, now, 1)) + ERR("The authentication certificate was not valid"); + if (! tor_tls_cert_is_valid(LOG_PROTOCOL_WARN, id_cert, id_cert, now, 1)) + ERR("The ID certificate was not valid"); + } + + return 1; +} + +/** Check all the ed25519 certificates in <b>certs</b> against each other, and + * against the peer certificate in <b>tls</b> if appropriate. On success, + * return 0; on failure, return a negative value and warn at level + * <b>severity</b> */ +int +or_handshake_certs_ed25519_ok(int severity, + or_handshake_certs_t *certs, + tor_tls_t *tls, + time_t now) +{ + ed25519_checkable_t check[10]; + unsigned n_checkable = 0; + time_t expiration = TIME_MAX; + +#define ADDCERT(cert, pk) \ + do { \ + tor_assert(n_checkable < ARRAY_LENGTH(check)); \ + if (tor_cert_get_checkable_sig(&check[n_checkable++], cert, pk, \ + &expiration) < 0) \ + ERR("Could not get checkable cert."); \ + } while (0) + + if (! certs->ed_id_sign || !certs->ed_id_sign->signing_key_included) { + ERR("No Ed25519 signing key"); + } + ADDCERT(certs->ed_id_sign, NULL); + + if (certs->started_here) { + if (! certs->ed_sign_link) + ERR("No Ed25519 link key"); + { + /* check for a match with the TLS cert. */ + tor_x509_cert_t *peer_cert = tor_tls_get_peer_cert(tls); + if (BUG(!peer_cert)) { + /* This is a bug, because if we got to this point, we are a connection + * that was initiated here, and we completed a TLS handshake. The + * other side *must* have given us a certificate! */ + ERR("No x509 peer cert"); // LCOV_EXCL_LINE + } + const common_digests_t *peer_cert_digests = + tor_x509_cert_get_cert_digests(peer_cert); + int okay = tor_memeq(peer_cert_digests->d[DIGEST_SHA256], + certs->ed_sign_link->signed_key.pubkey, + DIGEST256_LEN); + tor_x509_cert_free(peer_cert); + if (!okay) + ERR("Link certificate does not match TLS certificate"); + } + + ADDCERT(certs->ed_sign_link, &certs->ed_id_sign->signed_key); + + } else { + if (! certs->ed_sign_auth) + ERR("No Ed25519 link authentication key"); + ADDCERT(certs->ed_sign_auth, &certs->ed_id_sign->signed_key); + } + + if (expiration < now) { + ERR("At least one certificate expired."); + } + + /* Okay, we've gotten ready to check all the Ed25519 certificates. + * Now, we are going to check the RSA certificate's cross-certification + * with the ED certificates. + * + * FFFF In the future, we might want to make this optional. + */ + + tor_x509_cert_t *rsa_id_cert = certs->id_cert; + if (!rsa_id_cert) { + ERR("Missing legacy RSA ID certificate"); + } + if (! tor_tls_cert_is_valid(severity, rsa_id_cert, rsa_id_cert, now, 1)) { + ERR("The legacy RSA ID certificate was not valid"); + } + if (! certs->ed_rsa_crosscert) { + ERR("Missing RSA->Ed25519 crosscert"); + } + crypto_pk_t *rsa_id_key = tor_tls_cert_get_key(rsa_id_cert); + if (!rsa_id_key) { + ERR("RSA ID cert had no RSA key"); + } + + if (rsa_ed25519_crosscert_check(certs->ed_rsa_crosscert, + certs->ed_rsa_crosscert_len, + rsa_id_key, + &certs->ed_id_sign->signing_key, + now) < 0) { + crypto_pk_free(rsa_id_key); + ERR("Invalid RSA->Ed25519 crosscert"); + } + crypto_pk_free(rsa_id_key); + rsa_id_key = NULL; + + /* FFFF We could save a little time in the client case by queueing + * this batch to check it later, along with the signature from the + * AUTHENTICATE cell. That will change our data flow a bit, though, + * so I say "postpone". */ + + if (ed25519_checksig_batch(NULL, check, n_checkable) < 0) { + ERR("At least one Ed25519 certificate was badly signed"); + } + + return 1; +} + +/** + * Check the Ed certificates and/or the RSA certificates, as appropriate. If + * we obtained an Ed25519 identity, set *ed_id_out. If we obtained an RSA + * identity, set *rs_id_out. Otherwise, set them both to NULL. + */ +void +or_handshake_certs_check_both(int severity, + or_handshake_certs_t *certs, + tor_tls_t *tls, + time_t now, + const ed25519_public_key_t **ed_id_out, + const common_digests_t **rsa_id_out) +{ + tor_assert(ed_id_out); + tor_assert(rsa_id_out); + + *ed_id_out = NULL; + *rsa_id_out = NULL; + + if (certs->ed_id_sign) { + if (or_handshake_certs_ed25519_ok(severity, certs, tls, now)) { + tor_assert(certs->ed_id_sign); + tor_assert(certs->id_cert); + + *ed_id_out = &certs->ed_id_sign->signing_key; + *rsa_id_out = tor_x509_cert_get_id_digests(certs->id_cert); + + /* If we reached this point, we did not look at any of the + * subsidiary RSA certificates, so we'd better just remove them. + */ + tor_x509_cert_free(certs->link_cert); + tor_x509_cert_free(certs->auth_cert); + certs->link_cert = certs->auth_cert = NULL; + } + /* We do _not_ fall through here. If you provided us Ed25519 + * certificates, we expect to verify them! */ + } else { + /* No ed25519 keys given in the CERTS cell */ + if (or_handshake_certs_rsa_ok(severity, certs, tls, now)) { + *rsa_id_out = tor_x509_cert_get_id_digests(certs->id_cert); + } + } +} + +/* === ENCODING === */ + +/* Encode the ed25519 certificate <b>cert</b> and put the newly allocated + * string in <b>cert_str_out</b>. Return 0 on success else a negative value. */ +int +tor_cert_encode_ed22519(const tor_cert_t *cert, char **cert_str_out) +{ + int ret = -1; + char *ed_cert_b64 = NULL; + size_t ed_cert_b64_len; + + tor_assert(cert); + tor_assert(cert_str_out); + + /* Get the encoded size and add the NUL byte. */ + ed_cert_b64_len = base64_encode_size(cert->encoded_len, + BASE64_ENCODE_MULTILINE) + 1; + ed_cert_b64 = tor_malloc_zero(ed_cert_b64_len); + + /* Base64 encode the encoded certificate. */ + if (base64_encode(ed_cert_b64, ed_cert_b64_len, + (const char *) cert->encoded, cert->encoded_len, + BASE64_ENCODE_MULTILINE) < 0) { + log_err(LD_BUG, "Couldn't base64-encode ed22519 cert!"); + goto err; + } + + /* Put everything together in a NUL terminated string. */ + tor_asprintf(cert_str_out, + "-----BEGIN ED25519 CERT-----\n" + "%s" + "-----END ED25519 CERT-----", + ed_cert_b64); + /* Success! */ + ret = 0; + + err: + tor_free(ed_cert_b64); + return ret; +} + |