[tor-bugs] #5460 [Tor Client]: Write proposal(s) to evaluate circuit crypto authentication

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#5460: Write proposal(s) to evaluate circuit crypto authentication
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 Reporter:  mikeperry   |          Owner:       
     Type:  defect      |         Status:  new  
 Priority:  major       |      Milestone:       
Component:  Tor Client  |        Version:       
 Keywords:              |         Parent:  #5456
   Points:              |   Actualpoints:       
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 We need to write a proposal to determine the best way to provide
 authentication to our circuit crypto, so that cells that have been
 tagged/tampered with/duplicated cause circuit failure at the 2nd hop, not
 the third.

 As I understand it, there are two competing possibilities:

 1. Self-authenticating crypto (BEAR/LION/LIONESS, others?)
 2. Per-hop MAC

 The main disadvantage of 1 is that it's likely slow and not very many
 people use it. The disadvantage of 2 is that it requires us to disclose
 path length count and position to nodes, as well as have MACs that either
 grow with increased path length, or become less secure with increased path
 length.

 There are probably other issues. I believe the current plan is to produce
 both options in one or more proposals and compare and contrast them.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/5460>
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