Opened 4 months ago

Last modified 7 weeks ago

#24182 assigned defect

Pad INTRODUCE cells to hide the number of link specifiers

Reported by: teor Owned by: dgoulet
Priority: Medium Milestone: Tor: 0.3.4.x-final
Component: Core Tor/Tor Version:
Severity: Normal Keywords: prop224, tor-hs, defence-in-depth
Cc: Actual Points:
Parent ID: #23493 Points: 0.5
Reviewer: Sponsor:


Before #23577, there are two sizes of introduce cell data:

  • legacy id and IPv4 (24 bytes)
  • legacy id and IPv4 and ed25519 id (56 bytes)

After #23577: there are another two sizes:

  • legacy id and IPv4 and IPv6 (40 bytes)
  • legacy id and IPv4 and ed25519 id and IPv6 (72 bytes)

And if we ever remove IPv4 addresses, or add another link specifier, we create even more sizes.

This is ok at the moment, because we pad all cells to HS_CELL_INTRODUCE1_MIN_SIZE (246 bytes), and no cells are larger than this size. But we should make sure we are padding larger cells to the maximum cell length, to avoid splitting the rendezvous point anonymity set with future link specifiers.

Child Tickets

Change History (2)

comment:1 Changed 2 months ago by dgoulet

Owner: set to dgoulet
Status: newassigned

comment:2 Changed 7 weeks ago by dgoulet

Milestone: Tor: 0.3.3.x-finalTor: 0.3.4.x-final

Move 033 ticket I own to 034

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