tor

sigcommon.c (5907B)

---

/* Copyright (c) 2001 Matej Pfajfar.
* Copyright (c) 2001-2004, Roger Dingledine.
* Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
* Copyright (c) 2007-2021, The Tor Project, Inc. */
/* See LICENSE for licensing information */

/**
* \file sigcommon.c
* \brief Shared hashing, signing, and signature-checking code for directory
*    objects.
**/

#define SIGCOMMON_PRIVATE

#include "core/or/or.h"
#include "feature/dirparse/parsecommon.h"
#include "feature/dirparse/sigcommon.h"

/** Helper function for <b>router_get_hash_impl</b>: given <b>s</b>,
* <b>s_len</b>, <b>start_str</b>, <b>end_str</b>, and <b>end_c</b> with the
* same semantics as in that function, set *<b>start_out</b> (inclusive) and
* *<b>end_out</b> (exclusive) to the boundaries of the string to be hashed.
*
* Return 0 on success and -1 on failure.
*/
int
router_get_hash_impl_helper(const char *s, size_t s_len,
                           const char *start_str,
                           const char *end_str, char end_c,
                           int log_severity,
                           const char **start_out, const char **end_out)
{
 const char *start, *end;
 start = tor_memstr(s, s_len, start_str);
 if (!start) {
   log_fn(log_severity,LD_DIR,
          "couldn't find start of hashed material \"%s\"",start_str);
   return -1;
 }
 if (start != s && *(start-1) != '\n') {
   log_fn(log_severity,LD_DIR,
            "first occurrence of \"%s\" is not at the start of a line",
            start_str);
   return -1;
 }
 end = tor_memstr(start+strlen(start_str),
                  s_len - (start-s) - strlen(start_str), end_str);
 if (!end) {
   log_fn(log_severity,LD_DIR,
          "couldn't find end of hashed material \"%s\"",end_str);
   return -1;
 }
 end = memchr(end+strlen(end_str), end_c, s_len - (end-s) - strlen(end_str));
 if (!end) {
   log_fn(log_severity,LD_DIR,
          "couldn't find EOL");
   return -1;
 }
 ++end;

 *start_out = start;
 *end_out = end;
 return 0;
}

/** Compute the digest of the substring of <b>s</b> taken from the first
* occurrence of <b>start_str</b> through the first instance of c after the
* first subsequent occurrence of <b>end_str</b>; store the 20-byte or 32-byte
* result in <b>digest</b>; return 0 on success.
*
* If no such substring exists, return -1.
*/
int
router_get_hash_impl(const char *s, size_t s_len, char *digest,
                    const char *start_str,
                    const char *end_str, char end_c,
                    digest_algorithm_t alg)
{
 const char *start=NULL, *end=NULL;
 if (router_get_hash_impl_helper(s,s_len,start_str,end_str,end_c,LOG_WARN,
                                 &start,&end)<0)
   return -1;

 return router_compute_hash_final(digest, start, end-start, alg);
}

/** Compute the digest of the <b>len</b>-byte directory object at
* <b>start</b>, using <b>alg</b>. Store the result in <b>digest</b>, which
* must be long enough to hold it. */
MOCK_IMPL(STATIC int,
router_compute_hash_final,(char *digest,
                          const char *start, size_t len,
                          digest_algorithm_t alg))
{
 if (alg == DIGEST_SHA1) {
   if (crypto_digest(digest, start, len) < 0) {
     log_warn(LD_BUG,"couldn't compute digest");
     return -1;
   }
 } else {
   if (crypto_digest256(digest, start, len, alg) < 0) {
     log_warn(LD_BUG,"couldn't compute digest");
     return -1;
   }
 }

 return 0;
}

/** As router_get_hash_impl, but compute all hashes. */
int
router_get_hashes_impl(const char *s, size_t s_len, common_digests_t *digests,
                      const char *start_str,
                      const char *end_str, char end_c)
{
 const char *start=NULL, *end=NULL;
 if (router_get_hash_impl_helper(s,s_len,start_str,end_str,end_c,LOG_WARN,
                                 &start,&end)<0)
   return -1;

 if (crypto_common_digests(digests, start, end-start)) {
   log_warn(LD_BUG,"couldn't compute digests");
   return -1;
 }

 return 0;
}

MOCK_IMPL(STATIC int,
signed_digest_equals, (const uint8_t *d1, const uint8_t *d2, size_t len))
{
 return tor_memeq(d1, d2, len);
}

/** Check whether the object body of the token in <b>tok</b> has a good
* signature for <b>digest</b> using key <b>pkey</b>.
* If <b>CST_NO_CHECK_OBJTYPE</b> is set, do not check
* the object type of the signature object. Use <b>doctype</b> as the type of
* the document when generating log messages.  Return 0 on success, negative
* on failure.
*/
MOCK_IMPL(int,
check_signature_token,(const char *digest,
                     ssize_t digest_len,
                     directory_token_t *tok,
                     crypto_pk_t *pkey,
                     int flags,
                     const char *doctype))
{
 char *signed_digest;
 size_t keysize;
 const int check_objtype = ! (flags & CST_NO_CHECK_OBJTYPE);

 tor_assert(pkey);
 tor_assert(tok);
 tor_assert(digest);
 tor_assert(doctype);

 if (check_objtype) {
   if (strcmp(tok->object_type, "SIGNATURE")) {
     log_warn(LD_DIR, "Bad object type on %s signature", doctype);
     return -1;
   }
 }

 keysize = crypto_pk_keysize(pkey);
 signed_digest = tor_malloc(keysize);
 if (crypto_pk_public_checksig(pkey, signed_digest, keysize,
                               tok->object_body, tok->object_size)
     < digest_len) {
   log_warn(LD_DIR, "Error reading %s: invalid signature.", doctype);
   tor_free(signed_digest);
   return -1;
 }
 //  log_debug(LD_DIR,"Signed %s hash starts %s", doctype,
 //            hex_str(signed_digest,4));
 if (! signed_digest_equals((const uint8_t *)digest,
                            (const uint8_t *)signed_digest, digest_len)) {
   log_warn(LD_DIR, "Error reading %s: signature does not match.", doctype);
   tor_free(signed_digest);
   return -1;
 }
 tor_free(signed_digest);
 return 0;
}