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tor/src/or/torcert.c

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/* Copyright (c) 2014-2016, The Tor Project, Inc. */
/* See LICENSE for licensing information */
/**
* \file torcert.c
*
* \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"
#include "torlog.h"
#include "util.h"
#include "compat.h"
#include "link_handshake.h"
/** Helper for tor_cert_create(): signs any 32 bytes, not just an ed25519
* key.
*/
static tor_cert_t *
tor_cert_sign_impl(const ed25519_keypair_t *signing_key,
uint8_t cert_type,
uint8_t signed_key_type,
const uint8_t signed_key_info[32],
time_t now, time_t lifetime,
uint32_t flags)
{
tor_cert_t *torcert = NULL;
ed25519_cert_t *cert = ed25519_cert_new();
cert->cert_type = cert_type;
cert->exp_field = (uint32_t) CEIL_DIV(now + lifetime, 3600);
cert->cert_key_type = signed_key_type;
memcpy(cert->certified_key, signed_key_info, 32);
if (flags & CERT_FLAG_INCLUDE_SIGNING_KEY) {
ed25519_cert_extension_t *ext = ed25519_cert_extension_new();
ext->ext_type = CERTEXT_SIGNED_WITH_KEY;
memcpy(ext->un_signing_key, signing_key->pubkey.pubkey, 32);
ed25519_cert_add_ext(cert, ext);
++cert->n_extensions;
}
const ssize_t alloc_len = ed25519_cert_encoded_len(cert);
tor_assert(alloc_len > 0);
uint8_t *encoded = tor_malloc(alloc_len);
const ssize_t real_len = ed25519_cert_encode(encoded, alloc_len, cert);
if (real_len < 0)
goto err;
tor_assert(real_len == alloc_len);
tor_assert(real_len > ED25519_SIG_LEN);
uint8_t *sig = encoded + (real_len - ED25519_SIG_LEN);
tor_assert(tor_mem_is_zero((char*)sig, ED25519_SIG_LEN));
ed25519_signature_t signature;
if (ed25519_sign(&signature, encoded,
real_len-ED25519_SIG_LEN, signing_key)<0) {
log_warn(LD_BUG, "Can't sign certificate");
goto err;
}
memcpy(sig, signature.sig, ED25519_SIG_LEN);
torcert = tor_cert_parse(encoded, real_len);
if (! torcert) {
log_warn(LD_BUG, "Generated a certificate we cannot parse");
goto err;
}
if (tor_cert_checksig(torcert, &signing_key->pubkey, now) < 0) {
log_warn(LD_BUG, "Generated a certificate whose signature we can't check");
goto err;
}
tor_free(encoded);
goto done;
err:
tor_cert_free(torcert);
torcert = NULL;
done:
ed25519_cert_free(cert);
tor_free(encoded);
return torcert;
}
/**
* Create and return a new new certificate of type <b>cert_type</b> to
* authenticate <b>signed_key</b> using the key <b>signing_key</b>. The
* certificate should remain valid for at least <b>lifetime</b> seconds after
* <b>now</b>.
*
* If CERT_FLAG_INCLUDE_SIGNING_KEY is set in <b>flags</b>, embed
* the public part of <b>signing_key</b> in the certificate.
*/
tor_cert_t *
tor_cert_create(const ed25519_keypair_t *signing_key,
uint8_t cert_type,
const ed25519_public_key_t *signed_key,
time_t now, time_t lifetime,
uint32_t flags)
{
return tor_cert_sign_impl(signing_key, cert_type,
SIGNED_KEY_TYPE_ED25519, signed_key->pubkey,
now, lifetime, flags);
}
/** Release all storage held for <b>cert</b>. */
void
tor_cert_free(tor_cert_t *cert)
{
if (! cert)
return;
if (cert->encoded)
memwipe(cert->encoded, 0, cert->encoded_len);
tor_free(cert->encoded);
memwipe(cert, 0, sizeof(tor_cert_t));
tor_free(cert);
}
/** Parse a certificate encoded with <b>len</b> bytes in <b>encoded</b>. */
tor_cert_t *
tor_cert_parse(const uint8_t *encoded, const size_t len)
{
tor_cert_t *cert = NULL;
ed25519_cert_t *parsed = NULL;
ssize_t got_len = ed25519_cert_parse(&parsed, encoded, len);
if (got_len < 0 || (size_t) got_len != len)
goto err;
cert = tor_malloc_zero(sizeof(tor_cert_t));
cert->encoded = tor_memdup(encoded, len);
cert->encoded_len = len;
memcpy(cert->signed_key.pubkey, parsed->certified_key, 32);
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) {
ed25519_cert_extension_t *ext = ed25519_cert_get_ext(parsed, i);
if (ext->ext_type == CERTEXT_SIGNED_WITH_KEY) {
if (cert->signing_key_included)
goto err;
cert->signing_key_included = 1;
memcpy(cert->signing_key.pubkey, ext->un_signing_key, 32);
} else if (ext->ext_flags & CERTEXT_FLAG_AFFECTS_VALIDATION) {
/* Unrecognized extension with affects_validation set */
goto err;
}
}
goto done;
err:
tor_cert_free(cert);
cert = NULL;
done:
ed25519_cert_free(parsed);
return cert;
}
/** Fill in <b>checkable_out</b> with the information needed to check
* 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,
time_t *expiration_out)
{
if (! pubkey) {
if (cert->signing_key_included)
pubkey = &cert->signing_key;
else
return -1;
}
checkable_out->msg = cert->encoded;
checkable_out->pubkey = pubkey;
tor_assert(cert->encoded_len > ED25519_SIG_LEN);
const size_t signed_len = cert->encoded_len - ED25519_SIG_LEN;
checkable_out->len = signed_len;
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;
}
/** Validates the signature on <b>cert</b> with <b>pubkey</b> relative to the
* current time <b>now</b>. (If <b>now</b> is 0, do not check the expiration
* time.) Return 0 on success, -1 on failure. Sets flags in <b>cert</b> as
* appropriate.
*/
int
tor_cert_checksig(tor_cert_t *cert,
const ed25519_public_key_t *pubkey, time_t now)
{
ed25519_checkable_t checkable;
int okay;
time_t expires = TIME_MAX;
if (tor_cert_get_checkable_sig(&checkable, cert, pubkey, &expires) < 0)
return -1;
if (now && now > expires) {
cert->cert_expired = 1;
return -1;
}
if (ed25519_checksig_batch(&okay, &checkable, 1) < 0) {
cert->sig_bad = 1;
return -1;
} else {
cert->sig_ok = 1;
/* Only copy the checkable public key when it is different from the signing
* key of the certificate to avoid undefined behavior. */
if (cert->signing_key.pubkey != checkable.pubkey->pubkey) {
memcpy(cert->signing_key.pubkey, checkable.pubkey->pubkey, 32);
}
cert->cert_valid = 1;
return 0;
}
}
/** Return a new copy of <b>cert</b> */
tor_cert_t *
tor_cert_dup(const tor_cert_t *cert)
{
tor_cert_t *newcert = tor_memdup(cert, sizeof(tor_cert_t));
if (cert->encoded)
newcert->encoded = tor_memdup(cert->encoded, cert->encoded_len);
return newcert;
}
/** Return true iff cert1 and cert2 are the same cert. */
int
tor_cert_eq(const tor_cert_t *cert1, const tor_cert_t *cert2)
{
tor_assert(cert1);
tor_assert(cert2);
return cert1->encoded_len == cert2->encoded_len &&
tor_memeq(cert1->encoded, cert2->encoded, cert1->encoded_len);
}
/** Return true iff cert1 and cert2 are the same cert, or if they are both
* NULL. */
int
tor_cert_opt_eq(const tor_cert_t *cert1, const tor_cert_t *cert2)
{
if (cert1 == NULL && cert2 == NULL)
return 1;
if (!cert1 || !cert2)
return 0;
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
* the number of bytes stored. Returns negative on error.*/
ssize_t
tor_make_rsa_ed25519_crosscert(const ed25519_public_key_t *ed_key,
const crypto_pk_t *rsa_key,
time_t expires,
uint8_t **cert)
{
uint8_t *res;
rsa_ed_crosscert_t *cc = rsa_ed_crosscert_new();
memcpy(cc->ed_key, ed_key->pubkey, ED25519_PUBKEY_LEN);
cc->expiration = (uint32_t) CEIL_DIV(expires, 3600);
cc->sig_len = crypto_pk_keysize(rsa_key);
rsa_ed_crosscert_setlen_sig(cc, crypto_pk_keysize(rsa_key));
ssize_t alloc_sz = rsa_ed_crosscert_encoded_len(cc);
tor_assert(alloc_sz > 0);
res = tor_malloc_zero(alloc_sz);
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*)digest, sizeof(digest));
tor_assert(siglen > 0 && siglen <= (int)crypto_pk_keysize(rsa_key));
tor_assert(siglen <= UINT8_MAX);
cc->sig_len = siglen;
rsa_ed_crosscert_setlen_sig(cc, siglen);
sz = rsa_ed_crosscert_encode(res, alloc_sz, cc);
rsa_ed_crosscert_free(cc);
*cert = res;
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;
}
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