[tor-commits] [stem/master] Calculate network status document digests

[atagar@xxxxxxxxxxxxxx]

commit 04c334d0fc3613961e3e1315ed906de2817b5b9e
Author: Damian Johnson <atagar@xxxxxxxxxxxxxx>
Date:   Thu Nov 29 11:09:53 2018 -0800

    Calculate network status document digests
    
    Adding a digest() method to our base NetworkStatusDocument class. The spec is
    vague on how this is calculated (#28664), but through experimentation figured
    out that the range is up through the first 'directory-signature ' including the
    following space.
    
    To determine this I fetched the detached signatures and upcoming consensus
    during the voting period (minutes 55-60 of the hour), and compared our
    calculated result with that...
    
      ============================================================
      demo.py script
      ============================================================
    
      import stem.descriptor
    
      desc = next(stem.descriptor.parse_file(
        '/home/atagar/Desktop/next_consensus',
        descriptor_type = 'network-status-consensus-3 1.0',
        document_handler = stem.descriptor.DocumentHandler.DOCUMENT),
      )
    
      print('digest: %s' % desc.digest())
    
      ============================================================
    
      % curl http://128.31.0.39:9131/tor/status-vote/next/consensus-signatures > next_sigs
      % curl http://128.31.0.39:9131/tor/status-vote/next/consensus > consensus
    
      % grep consensus-digest sigs
      consensus-digest 296BA01987256A1C8EFB20E17667152DCFA50755
    
      % python demo.py
      digest: 296BA01987256A1C8EFB20E17667152DCFA50755
---
 stem/descriptor/networkstatus.py                  | 28 +++++++++++++++++++++++
 test/unit/descriptor/networkstatus/document_v3.py |  1 +
 2 files changed, 29 insertions(+)

diff --git a/stem/descriptor/networkstatus.py b/stem/descriptor/networkstatus.py
index 8cf07f03..45054b6b 100644
--- a/stem/descriptor/networkstatus.py
+++ b/stem/descriptor/networkstatus.py
@@ -68,6 +68,8 @@ import stem.version
 from stem.descriptor import (
   PGP_BLOCK_END,
   Descriptor,
+  DigestHash,
+  DigestEncoding,
   TypeAnnotation,
   DocumentHandler,
   _descriptor_content,
@@ -421,6 +423,32 @@ class NetworkStatusDocument(Descriptor):
   Common parent for network status documents.
   """
 
+  def digest(self, hash_type = DigestHash.SHA1, encoding = DigestEncoding.HEX):
+    """
+    Digest of this descriptor's content. These are referenced by...
+
+      * **DetachedSignature**
+
+        * Referer: :class:`~stem.descriptor.networkstatus.DetachedSignature` **consensus_digest** attribute
+        * Format: **SHA1/HEX**
+
+    .. versionadded:: 1.8.0
+
+    :param stem.descriptor.DigestHash hash_type: digest hashing algorithm
+    :param stem.descriptor.DigestEncoding encoding: digest encoding
+
+    :returns: **hashlib.HASH** or **str** based on our encoding argument
+    """
+
+    content = self._content_range(end = '\ndirectory-signature ')
+
+    if hash_type == DigestHash.SHA1:
+      return stem.descriptor._encode_digest(hashlib.sha1(content), encoding)
+    elif hash_type == DigestHash.SHA256:
+      return stem.descriptor._encode_digest(hashlib.sha256(content), encoding)
+    else:
+      raise NotImplementedError('Network status document digests are only available in sha1 and sha256, not %s' % hash_type)
+
 
 def _parse_version_line(keyword, attribute, expected_version):
   def _parse(descriptor, entries):
diff --git a/test/unit/descriptor/networkstatus/document_v3.py b/test/unit/descriptor/networkstatus/document_v3.py
index 92100141..daa88a09 100644
--- a/test/unit/descriptor/networkstatus/document_v3.py
+++ b/test/unit/descriptor/networkstatus/document_v3.py
@@ -120,6 +120,7 @@ ci356fosgLiM1sVqCUkNdA==
       self.assertEqual(expected_bandwidth_weights, document.bandwidth_weights)
       self.assertEqual([], document.consensus_methods)
       self.assertEqual(None, document.published)
+      self.assertEqual('270D2E02D8E6AD83DD87BD56CF8B7874F75063A9', document.digest())
       self.assertEqual([], document.get_unrecognized_lines())
       self.assertEqual('@type network-status-consensus-3 1.0', str(document.type_annotation()))
 

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