commit 49196be6b76058d68837a6f3f5ed6e4a0dc55f38 Author: George Kadianakis desnacked@riseup.net Date: Tue Jun 1 12:56:15 2021 +0300

First iteration of vanguards lite proposal. --- proposals/332-vanguards-lite.md | 60 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 60 insertions(+)

diff --git a/proposals/332-vanguards-lite.md b/proposals/332-vanguards-lite.md new file mode 100644 index 0000000..3971b75 --- /dev/null +++ b/proposals/332-vanguards-lite.md @@ -0,0 +1,60 @@ +``` +Filename: 332-vanguards-lite.md +Title: Vanguards lite +Author: George Kadianakis, Mike Perry +Created: 2021-05-20 +Status: Draft +``` + +# 0. Introduction & Motivation + + This proposal specifies a simplified version of Proposal 292 "Mesh-based + vanguards" for the purposes of implementing it directly into the C Tor + codebase. + + For more details on guard discovery attacks and how vanguards defend against + it, we refer to Proposal 292 [PROP292_REF]. + +# 1. Overview + + We propose an identical system to the Mesh-based Vanguards from proposal 292, + but with the following differences: + + - No third layer of guards is used. + - The Layer2 lifetime uses the max(x,x) distribution with a minimum of one + day and maximum of 12 days. This makes the average lifetime approximately a + week. We let NUM_LAYER2_GUARDS=4. + - We don't write guards on disk. This means that the guard topology resets + when tor restarts. + + By avoiding a third-layer of guards we reduce the linkability issues + of Proposal 292, which means that we don't have to add an extra hop on top of + our paths. This simplifies engineering. + +# 2. Rotation Period Analysis + + From the table in Section 3.1 of Proposal 292, with NUM_LAYER2_GUARDS=4 it + can be seen that this means that the Sybil attack on Layer2 will complete + with 50% chance in 18*7 days (126 days) for the 1% adversary, 4*7 days (one + month) for the 5% adversary, and 2*7 days (two weeks) for the 10% adversary. + +# 3. Tradeoffs from Proposal 292 + + This proposal has several advantages over Proposal 292: + + By avoiding a third-layer of guards we reduce the linkability issues of + Proposal 292, which means that we don't have to add an extra hop on top of + our paths. This simplifies engineering and makes paths shorter by default: + this means less latency and quicker page load times. + + This proposal also comes with disadvantages: + + The lack of third-layer guards makes it easier to launch guard discovery + attacks against clients and onion services. Long-lived services are not well + protected, and this proposal might provide those services with a false sense + of security. Such services should still use the vanguards addon [VANGUARDS_REF]. + +# 4. References + + [PROP292_REF]: https://gitlab.torproject.org/tpo/core/torspec/-/blob/main/proposals/292-mes... + [VANGUARDS_REF]: https://github.com/mikeperry-tor/vanguards