| 
					
				 | 
			
			
				@@ -1,11 +1,20 @@ 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				 Filename: 158-microdescriptors.txt 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				 Title: Clients download consensus + microdescriptors 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-Version: $Revision$ 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-Last-Modified: $Date$ 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				 Author: Roger Dingledine 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				 Created: 17-Jan-2009 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				 Status: Open 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				  
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+0. History 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+ 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  15 May 2009: Substantially revised based on discussions on or-dev 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  from late January.  Removed the notion of voting on how to choose 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  microdescriptors; made it just a function of the consensus method. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  (This lets us avoid the possibility of "desynchronization.") 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  Added suggestion to use a new consensus flavor.  Specified use of 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  SHA256 for new hashes. -nickm 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+ 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  15 June 2009: Cleaned up based on comments from Roger. -nickm 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+ 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				 1. Overview 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				  
			 | 
		
	
		
			
				 | 
				 | 
			
			
				   This proposal replaces section 3.2 of proposal 141, which was 
			 | 
		
	
	
		
			
				| 
					
				 | 
			
			
				@@ -13,9 +22,7 @@ Status: Open 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				   circuit-building protocol to fetch a server descriptor inline at each 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				   circuit extend, we instead put all of the information that clients need 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				   either into the consensus itself, or into a new set of data about each 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  relay called a microdescriptor. The microdescriptor is a direct 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  transform from the relay descriptor, so relays don't even need to know 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  this is happening. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  relay called a microdescriptor. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				  
			 | 
		
	
		
			
				 | 
				 | 
			
			
				   Descriptor elements that are small and frequently changing should go 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				   in the consensus itself, and descriptor elements that are small and 
			 | 
		
	
	
		
			
				| 
					
				 | 
			
			
				@@ -24,6 +31,10 @@ Status: Open 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				   them, we'll need to resume considering some design like the one in 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				   proposal 141. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				  
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  Note also that any descriptor element which clients need to use to 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  decide which servers to fetch info about, or which servers to fetch 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  info from, needs to stay in the consensus. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+ 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				 2. Motivation 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				  
			 | 
		
	
		
			
				 | 
				 | 
			
			
				   See 
			 | 
		
	
	
		
			
				| 
					
				 | 
			
			
				@@ -36,99 +47,91 @@ Status: Open 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				 3. Design 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				  
			 | 
		
	
		
			
				 | 
				 | 
			
			
				   There are three pieces to the proposal. First, authorities will list in 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  their votes (and thus in the consensus) what relay descriptor elements 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  are included in the microdescriptor, and also list the expected hash 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  of microdescriptor for each relay. Second, directory mirrors will serve 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  microdescriptors. Third, clients will ask for them and cache them. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  their votes (and thus in the consensus) the expected hash of 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  microdescriptor for each relay. Second, authorities will serve 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  microdescriptors, directory mirrors will cache and serve 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  them. Third, clients will ask for them and cache them. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				  
			 | 
		
	
		
			
				 | 
				 | 
			
			
				 3.1. Consensus changes 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				  
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  V3 votes should include a new line: 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-    microdescriptor-elements bar baz foo 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  listing each descriptor element (sorted alphabetically) that authority 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  included when it calculated its expected microdescriptor hashes. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  If the authorities choose a consensus method of a given version or 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  later, a microdescriptor format is implicit in that version. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  A microdescriptor should in every case be a pure function of the 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  router descriptor and the consensus method. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+ 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  In votes, we need to include the hash of each expected microdescriptor 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  in the routerstatus section. I suggest a new "m" line for each stanza, 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  with the base64 of the SHA256 hash of the router's microdescriptor. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+ 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  For every consensus method that an authority supports, it includes a 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  separate "m" line in each router section of its vote, containing: 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+    "m" SP methods 1*(SP AlgorithmName "=" digest) NL 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  where methods is a comma-separated list of the consensus methods 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  that the authority believes will produce "digest". 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				  
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  We also need to include the hash of each expected microdescriptor in 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  the routerstatus section. I suggest a new "m" line for each stanza, 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  with the base64 of the hash of the elements that the authority voted 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  for above. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  (As with base64 encoding of SHA1 hashes in consensuses, let's 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  omit the trailing =s) 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				  
			 | 
		
	
		
			
				 | 
				 | 
			
			
				   The consensus microdescriptor-elements and "m" lines are then computed 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				   as described in Section 3.1.2 below. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				  
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  I believe that means we need a new consensus-method "6" that knows 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  how to compute the microdescriptor-elements and add "m" lines. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  (This means we need a new consensus-method that knows 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  how to compute the microdescriptor-elements and add "m" lines.) 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				  
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-3.1.1. Descriptor elements to include for now 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  The microdescriptor consensus uses the directory-signature format from 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  proposal 162, with the "sha256" algorithm. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				  
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  To start, the element list that authorities suggest should be 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-    family onion-key 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				  
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  (Note that the or-dev posts above only mention onion-key, but if 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  we don't also include family then clients will never learn it. It 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  seemed like it should be relatively static, so putting it in the 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  microdescriptor is smarter than trying to fit it into the consensus.) 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+3.1.1. Descriptor elements to include for now 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				  
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  We could imagine a config option "family,onion-key" so authorities 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  could change their voted preferences without needing to upgrade. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  In the first version, the microdescriptor should contain the 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  onion-key element, and the family element from the router descriptor, 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  and the exit policy summary as currently specified in dir-spec.txt. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				  
			 | 
		
	
		
			
				 | 
				 | 
			
			
				 3.1.2. Computing consensus for microdescriptor-elements and "m" lines 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				  
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  One approach is for the consensus microdescriptor-elements line to 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  include every element listed by a majority of authorities, sorted. The 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  problem here is that it will no longer be deterministic what the correct 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  hash for the "m" line should be. We could imagine telling the authority 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  to go look in its descriptor and produce the right hash itself, but 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  we don't want consensus calculation to be based on external data like 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  that. (Plus, the authority may not have the descriptor that everybody 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  else voted to use.) 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				- 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  The better approach is to take the exact set that has the most votes 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  (breaking ties by the set that has the most elements, and breaking 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  ties after that by whichever is alphabetically first). That will 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  increase the odds that we actually get a microdescriptor hash that 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  is both a) for the descriptor we're putting in the consensus, and b) 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  over the elements that we're declaring it should be for. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				- 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  Then the "m" line for a given relay is the one that gets the most votes 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  from authorities that both a) voted for the microdescriptor-elements 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  line we're using, and b) voted for the descriptor we're using. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				- 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  (If there's a tie, use the smaller hash. But really, if there are 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  multiple such votes and they differ about a microdescriptor, we caught 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  one of them lying or being buggy. We should log it to track down why.) 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				- 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  If there are no such votes, then we leave out the "m" line for that 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  relay. That means clients should avoid it for this time period. (As 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  an extension it could instead mean that clients should fetch the 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  descriptor and figure out its microdescriptor themselves. But let's 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  not get ahead of ourselves.) 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				- 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  It would be nice to have a more foolproof way to agree on what 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  microdescriptor hash each authority should vote for, so we can avoid 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  missing "m" lines. Just switching to a new consensus-method each time 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  we change the set of microdescriptor-elements won't help though, since 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  each authority will still have to decide what hash to vote for before 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  knowing what consensus-method will be used. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				- 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  Here's one way we could do it. Each vote / consensus includes 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  the microdescriptor-elements that were used to compute the hashes, 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  and also a preferred-microdescriptor-elements set. If an authority 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  has a consensus from the previous period, then it should use the 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  consensus preferred-microdescriptor-elements when computing its votes 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  for microdescriptor-elements and the appropriate hashes in the upcoming 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  period. (If it has no previous consensus, then it just writes its 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  own preferences in both lines.) 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				- 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-3.2. Directory mirrors serve microdescriptors 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				- 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  Directory mirrors should then read the microdescriptor-elements line 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  from the consensus, and learn how to answer requests. (Directory mirrors 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  continue to serve normal relay descriptors too, a) to serve old clients 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  and b) to be able to construct microdescriptors on the fly.) 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				- 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  The microdescriptors with hashes <D1>,<D2>,<D3> should be available at: 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-    http://<hostname>/tor/micro/d/<D1>+<D2>+<D3>.z 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  When we are generating a consensus, we use whichever m line 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  unambiguously corresponds to the descriptor digest that will be 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  included in the consensus. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+ 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  (If different votes have different microdescriptor digests for a 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  single <descriptor-digest, consensus-method> pair, then at least one 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  of the authorities is broken.  If this happens, the consensus should 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  contain whichever microdescriptor digest is most common.  If there is 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  no winner, we break ties in the favor of the lexically earliest. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  Either way, we should log a warning: there is definitely a bug.) 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+ 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  The "m" lines in a consensus contain only the digest, not a list of 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  consensus methods. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+ 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+3.1.3. A new flavor of consensus 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+ 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  Rather than inserting "m" lines in the current consensus format, 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  they should be included in a new consensus flavor (see proposal 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  162). 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+ 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  This flavor can safely omit descriptor digests. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+ 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  When we implement this voting method, we can remove the exit policy 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  summary from the current "ns" flavor of consensus, since no current 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  clients use them, and they take up about 5% of the compressed 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  consensus. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+ 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  This new consensus flavor should be signed with the sha256 signature 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  format as documented in proposal 162. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+ 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+3.2. Directory mirrors fetch, cache, and serve microdescriptors 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+ 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  Directory mirrors should fetch, catch, and serve each microdescriptor 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  from the authorities.  (They need to continue to serve normal relay 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  descriptors too, to handle old clients.) 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+ 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  The microdescriptors with base64 hashes <D1>,<D2>,<D3> should be 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  available at: 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+    http://<hostname>/tor/micro/d/<D1>-<D2>-<D3>.z 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  (We use base64 for size and for consistency with the consensus 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  format. We use -s instead of +s to separate these items, since 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  the + character is used in base64 encoding.) 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				  
			 | 
		
	
		
			
				 | 
				 | 
			
			
				   All the microdescriptors from the current consensus should also be 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				   available at: 
			 | 
		
	
	
		
			
				| 
					
				 | 
			
			
				@@ -136,24 +139,9 @@ Status: Open 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				   so a client that's bootstrapping doesn't need to send a 70KB URL just 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				   to name every microdescriptor it's looking for. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				  
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  The format of a microdescriptor is the header line 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  "microdescriptor-header" 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  followed by each element (keyword and body), alphabetically. There's 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  no need to mention what hash it's for, since it's self-identifying: 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  you can hash the elements to learn this. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				- 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  (Do we need a footer line to show that it's over, or is the next 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  microdescriptor line or EOF enough of a hint? A footer line wouldn't 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  hurt much. Also, no fair voting for the microdescriptor-element 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  "microdescriptor-header".) 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				- 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  Microdescriptors have no header or footer. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				   The hash of the microdescriptor is simply the hash of the concatenated 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  elements -- not counting the header line or hypothetical footer line. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  Unless you prefer that? 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				- 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  Is there a reasonable way to version these things? We could say that 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  the microdescriptor-header line can contain arguments which clients 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  must ignore if they don't understand them. Any better ways? 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  elements. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				  
			 | 
		
	
		
			
				 | 
				 | 
			
			
				   Directory mirrors should check to make sure that the microdescriptors 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				   they're about to serve match the right hashes (either the hashes from 
			 | 
		
	
	
		
			
				| 
					
				 | 
			
			
				@@ -170,10 +158,14 @@ Status: Open 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				   When a client gets a new consensus, it looks to see if there are any 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				   microdescriptors it needs to learn. If it needs to learn more than 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				   some threshold of the microdescriptors (half?), it requests 'all', 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  else it requests only the missing ones. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  else it requests only the missing ones.  Clients MAY try to 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  determine whether the upload bandwidth for listing the 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  microdescriptors they want is more or less than the download 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  bandwidth for the microdescriptors they do not want. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				  
			 | 
		
	
		
			
				 | 
				 | 
			
			
				   Clients maintain a cache of microdescriptors along with metadata like 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  when it was last referenced by a consensus. They keep a microdescriptor 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  when it was last referenced by a consensus, and which identity key 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  it corresponds to.  They keep a microdescriptor 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				   until it hasn't been mentioned in any consensus for a week. Future 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				   clients might cache them for longer or shorter times. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				  
			 | 
		
	
	
		
			
				| 
					
				 | 
			
			
				@@ -190,18 +182,17 @@ Status: Open 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				   Another future option would be to fetch some of the microdescriptors 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				   anonymously (via a Tor circuit). 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				  
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  Another crazy option (Roger's phrasing) is to do decoy fetches as 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  well. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+ 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				 4. Transition and deployment 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				  
			 | 
		
	
		
			
				 | 
				 | 
			
			
				   Phase one, the directory authorities should start voting on 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  microdescriptors and microdescriptor elements, and putting them in the 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  consensus. This should happen during the 0.2.1.x series, and should 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  be relatively easy to do. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  microdescriptors, and putting them in the consensus. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				  
			 | 
		
	
		
			
				 | 
				 | 
			
			
				   Phase two, directory mirrors should learn how to serve them, and learn 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  how to read the consensus to find out what they should be serving. This 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  phase could be done either in 0.2.1.x or early in 0.2.2.x, depending 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  on how messy it turns out to be and how quickly we get around to it. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  how to read the consensus to find out what they should be serving. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				  
			 | 
		
	
		
			
				 | 
				 | 
			
			
				   Phase three, clients should start fetching and caching them instead 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				-  of normal descriptors. This should happen post 0.2.1.x. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				+  of normal descriptors. 
			 | 
		
	
		
			
				 | 
				 | 
			
			
				  
			 |