Clarify 'recognized' field in tor-spec

Our tor-spec left me pretty mystified what the 'recognized' field actually was. It discussed what to do when it was zero, but not what the field was or what non-zero meant. Thankfully Roger filled me in over tasty, tasty pizza.

Patch available in the 'recognized' branch of my repo...

https://gitweb.torproject.org/user/atagar/torspec.git/commit/?h=recognized

changed milestone to %Tor: 0.3.3.x-final in legacy/trac

added component::core tor/tor in Legacy / Trac doc in Legacy / Trac milestone::Tor: 0.3.3.x-final in Legacy / Trac priority::very low in Legacy / Trac resolution::fixed in Legacy / Trac review-group-32 in Legacy / Trac reviewer::nickm in Legacy / Trac severity::trivial in Legacy / Trac status::closed in Legacy / Trac tor-spec in Legacy / Trac type::defect in Legacy / Trac labels

Trac:
Status: new to needs_review

Trac:
Milestone: N/A to Tor: 0.3.3.x-final

As Roger said on IRC: recognised is very likely zero if the cell is decrypted and destined for this hop. But there is a 1 in 2^32 chance of zero even if the cell is not destined for this hop.

Trac:
Keywords: N/A deleted, doc, tor-spec added
Status: needs_review to needs_revision

Thanks, good point. Changed it to a 'MAY' clause with an explanation for why.

Trac:
Status: needs_revision to needs_review

Trac:
Keywords: N/A deleted, review-group-32 added

Trac:
Reviewer: N/A to nickm

Thanks, atagar! I think this is as improvement over the existing spec.

I've merged it, and made a couple of small tweaks in ef91cd6a595128. The main one is that I don't think MAY is right here either: as I read RFC 2119, "MAY "is for things that implementations are allowed to do, not for circumstances that will periodically occur.

I've gone with this tweak on your wording:

+   When receiving and decrypting cells the 'recognized' will always be
+   zero if we're the endpoint that the cell is destined for.  For cells
+   that we should relay, the 'recognized' field will usually be nonzero,
+   but will accidentally be zero with P=2^-32.

Thanks again for the spec fix!

Trac:
Resolution: N/A to fixed
Status: needs_review to closed

closed

moved from legacy/trac#25171 (moved)

added Bug label and removed 1 deleted label

added Specifications + 1 deleted label and removed 1 deleted label

added Documentation label and removed 1 deleted label