[tor-commits] [stem/master] Compute extrainfo sha256 digests from the whole descriptor

[atagar at torproject.org]

commit f214309e04a6e9924206c26ff4bb22637c826383
Author: Damian Johnson <atagar at torproject.org>
Date:   Tue Nov 13 17:32:27 2018 -0800

    Compute extrainfo sha256 digests from the whole descriptor
    
    Accounting for a tor bug that's prompting an upcoming spec change...
    
      https://trac.torproject.org/projects/tor/ticket/28415
---
 stem/descriptor/extrainfo_descriptor.py      | 22 ++++++++++++++--------
 test/unit/descriptor/extrainfo_descriptor.py |  3 ++-
 2 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/stem/descriptor/extrainfo_descriptor.py b/stem/descriptor/extrainfo_descriptor.py
index 2df4bc71..f1e29cd2 100644
--- a/stem/descriptor/extrainfo_descriptor.py
+++ b/stem/descriptor/extrainfo_descriptor.py
@@ -954,17 +954,23 @@ class RelayExtraInfoDescriptor(ExtraInfoDescriptor):
 
   @lru_cache()
   def digest(self, hash_type = DigestHashType.SHA1):
-    # our digest is calculated from everything except our signature
-    raw_content, ending = str(self), '\nrouter-signature\n'
-    raw_content = stem.util.str_tools._to_bytes(raw_content[:raw_content.find(ending) + len(ending)])
-
     if hash_type == DigestHashType.SHA1:
+      # our digest is calculated from everything except our signature
+
+      raw_content, ending = str(self), '\nrouter-signature\n'
+      raw_content = stem.util.str_tools._to_bytes(raw_content[:raw_content.find(ending) + len(ending)])
       return hashlib.sha1(raw_content).hexdigest().upper()
     elif hash_type == DigestHashType.SHA256:
-      # descriptors drop '=' hash padding from its fields (such as our server
-      # descriptor's extra-info-digest), so doing the same here so we match
-
-      return base64.b64encode(hashlib.sha256(raw_content).digest()).rstrip('=')
+      # Due to a tor bug sha256 digests are calculated from the
+      # whole descriptor rather than ommiting the signature...
+      #
+      #   https://trac.torproject.org/projects/tor/ticket/28415
+      #
+      # Descriptors drop '=' hash padding from its fields (such
+      # as our server descriptor's extra-info-digest), so doing
+      # the same here so we match.
+
+      return base64.b64encode(hashlib.sha256(str(self)).digest()).rstrip('=')
     else:
       raise NotImplementedError('Extrainfo descriptor digests are only available in sha1 and sha256, not %s' % hash_type)
 
diff --git a/test/unit/descriptor/extrainfo_descriptor.py b/test/unit/descriptor/extrainfo_descriptor.py
index f3252d4e..7a85dd06 100644
--- a/test/unit/descriptor/extrainfo_descriptor.py
+++ b/test/unit/descriptor/extrainfo_descriptor.py
@@ -53,7 +53,8 @@ k0d2aofcVbHr4fPQOSST0LXDrhFl5Fqo5um296zpJGvRUeO6S44U/EfJAGShtqWw
     self.assertEqual(datetime.datetime(2012, 5, 5, 17, 2, 45), desc.dir_write_history_end)
     self.assertEqual(900, desc.dir_write_history_interval)
     self.assertEqual(expected_signature, desc.signature)
-    self.assertEqual('00A57A9AAB5EA113898E2DD02A755E31AFC27227', desc.digest())
+    self.assertEqual('00A57A9AAB5EA113898E2DD02A755E31AFC27227', desc.digest(stem.descriptor.DigestHashType.SHA1))
+    self.assertEqual('n2+wh6uM+lbKnhbkOog2jv9X5tPytlrFdO+I+auSmME', desc.digest(stem.descriptor.DigestHashType.SHA256))
     self.assertEqual([], desc.get_unrecognized_lines())
 
     # The read-history, write-history, dirreq-read-history, and