June 2014 - tor-dev - lists.torproject.org

Proposal 236, Single-guard designs, and directory guards
by Nick Mathewson 06 Jun '14

06 Jun '14

Hi, all! I noticed that proposal 236 doesn't mention directory guards. (See proposal 207, implemented in Tor 0.2.4.) I think that we should consider retaining multiple directory guards while going to a single guard for multi-hop circuits. My rationale here is that when we have only a single directory guard, it can more easily perform hard-to-detect route biasing attacks by pretending not to have descriptors for nodes it doesn't like. Its ability to do this is limited by fact that we won't build circuits unless 95% of all paths are buildable (see get_frac_paths_needed_for_circuits() and its users). But still, trusting a single source for the completeness and freshness of your directory info is suboptimal. I also think that most of the arguments for single-guard apply to circuit guards more than to directory guards. But there could be some left, and we should figure those out. peace, -- Nick

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Pluggable transports meeting today (Friday 6th of June 2014)
by George Kadianakis 06 Jun '14

06 Jun '14

Hello friends, just wanted to remind you that the regular biweekly pluggable transports meeting is going to occur today at 16:00 UTC. Place is the #tor-dev IRC channel in the OFTC network. Please note that we recently *changed* the time from 17:00 to 16:00 UTC. Thanks!

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[Patch] test/test.c. TEMP-dir
by Gisle Vanem 05 Jun '14

05 Jun '14

Hello list. I don't get any FAILED tests running on Win32 (MSVC), but IMHO the use of '\\' in the TEMP-directory doesn't look quite kosher (looks a bit like a "\\server\share\path" UNC-syntax). >From test_crypto_pk() running 'test.exe --warn': Jun 05 10:13:05.046 [warn] Could not open "F:\TEMP\\tor_test_3992_vv7drny6/xyzzy": No such file or directory Jun 05 10:13:05.046 [warn] Error reading private key from "F:\TEMP\\tor_test_3992_vv7drny6/xyzzy" So can you accept this small change: diff --git a/src/test/test.c b/src/test/test.c index 8bce9c9..98620e5 100644 --- a/src/test/test.c +++ b/src/test/test.c @@ -108,9 +108,9 @@ setup_directory(void) const char *tmp = buf; /* If this fails, we're probably screwed anyway */ if (!GetTempPathA(sizeof(buf),buf)) - tmp = "c:\\windows\\temp"; + tmp = "c:\\windows\\temp\\"; tor_snprintf(temp_dir, sizeof(temp_dir), - "%s\\tor_test_%d_%s", tmp, (int)getpid(), rnd32); + "%stor_test_%d_%s", tmp, (int)getpid(), rnd32); r = mkdir(temp_dir); } #else ------------------ Ref: http://msdn.microsoft.com/en-us/library/windows/desktop/aa364992(v=vs.85).a… lpBuffer [out] A pointer to a string buffer that receives the null-terminated string specifying the temporary file path. The returned string ends with a backslash, for example, "C:\TEMP\". ---------- I also tested 'test.exe --warn' without any TMP or TEMP. Thus my USERPROFILE is used: Jun 05 10:46:47.984 [warn] Could not open "f:\Documents and Settings\Gisle Vanem\tor_test_6368_s62ks2fe/xyzzy": No such file or directory Jun 05 10:46:47.984 [warn] Error reading private key from "f:\Documents and Settings\Gisle Vanem\tor_test_6368_s62ks2fe/xyzzy" --gv

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Reminder: tor development meetings this (and every) Wednesday, 19:00 UTC
by Nick Mathewson 04 Jun '14

04 Jun '14

Hi, all! Here's your regular reminder for the weekly IRC meeting for people working on the program "tor". (This won't cover all the other programs developed under the Tor umbrella.) The next meeting time will be: Wednesday June 28, 19:00 UTC. (That's 3pm EDT and 12:00 noon PDT.) As usual, we'll do it on the #tor-dev IRC channel. I've seen a drop-off in the number of people coming since I stopped sending these out weekly, so I'm sending them again for a while. Among other stuff, I expect we'll be figuring out the rest of the 0.2.5 series, planning an 0.2.5.5 release maybe trying to chase some bugs, and figuring out how to open development on 0.2.6.x. cheers, -- Nick

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tor-weather meeting Wed, 1800UTC
by meejah 03 Jun '14

03 Jun '14

Wednesday, 1800UTC, #tor-dev I will run the meeting. I haven't made MeetBot run anywhere; if someone has an instnace we can try out tomorrow, please mail me or follow-up here. If you have something to add to the agenda, either mail me directly or just show up at the meeting (we will figure out the agenda as the first thing). thanks, meejah

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obfs4 and ntor (question wrt node_id)
by George Kadianakis 02 Jun '14

02 Jun '14

Hello Ian, hope you are well :) I have a question wrt a new PT and ntor. Yawning Angel has been developing a new PT called obfs4 (temp name), which is basically scramblesuit using ntor and elligator2. This results in better performance than UniformDH. You can find the spec of obfs4 here: https://github.com/Yawning/obfs4/blob/master/doc/obfs4-spec.txt You can read a description of the ntor handshake here: https://github.com/Yawning/obfs4/blob/master/doc/obfs4-spec.txt#L149 The protocol works fine, but it requires two shared-secrets between the client and the server. The first is the long-term public key of obfs4, and the other is the "node id" of the server (defined as fingerprint of the bridge's identity key). My question has to do with the "node id" (denoted as 'capped B' in the ntor paper) . The problem is that it complicates the deployment of obfs4, since the bridge operator has to find her bridge's fingerprint (by looking at $DataDirectory/fingerprint) and add it to her torrc (as part of the ServerTransportOptions line). Also, the bridge operator needs to give a similar Bridge line to her clients. I was trying to understand if it's possible to simplify this, by not requiring the bridge operator to make the effort of finding her bridge's fingerprint. There are at least two possible ways to do this: a) Instead of using the bridge's identity key as the node id (which provides some kind of (unneeded?) channel binding), just generate a random string to serve as the node id of the bridge. As I understand it, node id is just a 1-1 map to a specific public key, so a big random string should be able to do the trick, right? b) Just discard the node id, and use the public key in its place. So wherever 'capped B' is used, just use 'B' instead. Intuitively this seems OK to me, but I admit I couldn't follow the whole security proof on Appendix B, to verify that it doesn't make any difference. Do you think any of the above approaches is correct, without bludgeoning ntor's security? Thanks!

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Question about HS code
by Michael Rogers 02 Jun '14

02 Jun '14

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Hi, I've been trying to get to grips with the hidden service code, and I have a question that I was hoping someone on the list could answer. The constant REND_HID_SERV_DIR_REQUERY_PERIOD is defined as 15 * 60 (15 minutes) in rendclient.c, with the comment "The period for which a hidden service directory cannot be queried for the same descriptor ID again." As far as I can tell, the purpose of this constant is to prevent a client from repeatedly asking an HS directory for a descriptor that the directory doesn't have. However, when a descriptor fetch fails and there's no reusable cached descriptor, rend_client_desc_trynow(query) calls rend_client_note_connection_attempt_ended(onion_address), which calls purge_hid_serv_from_last_hid_serv_requests(onion_address), which (as far as I can tell) forgets which HS directories have been tried for the descriptor, allowing the same directories to be tried again before REND_HID_SERV_DIR_REQUERY_PERIOD elapses. So what's the effect of REND_HID_SERV_DIR_REQUERY_PERIOD? Thanks for any guidance, Michael -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) iQEcBAEBCAAGBQJThJI1AAoJEBEET9GfxSfMHxwH/3DH2ZpWsmjfu8wX/Zaw2m1T 5NBYhrzpQqJ5C3doVd5cSsCuZINQOG/kHFda3HAf4a0UwANkGZQzSKiB78IXL/VG yEVts1ZpDEF3rtGgnQMBnFQ9JChNzYRuJ5uT+EFJBjW9fgWVuh+8KugNev9wLiR8 V8ayDaekZxUaT11+qEqS974IRI1wWVIzUvGFylMsCsuf/NAKkUalXscOOT3ckKUN g2b1M5f38uzpFqdvRtTIgL/p0dS3JtrrGcuYnwD2+THzeAQpIHGuFPxnbjoauCBd HwyGCo0v3UKr4e00YSKlhJBAZjB2Y41jwi5vasp7IefFvsuVOXfcc8b4BP5Syyk= =d/B4 -----END PGP SIGNATURE-----

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Unit tests that need writing in core
by Ajay Bhat 02 Jun '14

02 Jun '14

Hi, I'd like to contribute to tor core by writing any unit tests that need to be done. Can anyone please help me out by pointing out the code/modules that needs to be tested? -Ajay

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Damian's Status Report - May 2014
by Damian Johnson 02 Jun '14

02 Jun '14

Hi all, this month was focused on work leading up to today's Stem 1.2.0 release. The control interpreter in particular turned out extremely well, so if you haven't tried it yet then please check it out! https://blog.torproject.org/blog/stem-release-12 https://stem.torproject.org/tutorials/down_the_rabbit_hole.html Besides implementing and writing a tutorial for the interpreter this involved addressing a host of other issues that had accumulated in trac. By far the most important was an issue where Stem spawned Tor instances would halt due to unread stdout content (#9862). Last, I looked over the code of several new Stem users this month and added them to our examples page... * Yawning's or-applet (https://lists.torproject.org/pipermail/tor-dev/2014-May/006915.html) * Whonix (https://lists.torproject.org/pipermail/tor-dev/2014-May/006799.html) * Kostas' torsearch (https://github.com/wfn/torsearch) Cheers! -Damian

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Stem Release 1.2
by Damian Johnson 01 Jun '14

01 Jun '14

Hi all. After months of work I'm please to announce the release of Stem 1.2.0! For those who aren't familiar with it, Stem is a Python library for interacting with Tor. With it you can script against your relay, descriptor data, or even write applications similar to arm and Vidalia. https://stem.torproject.org/ So what's new in this release? ============================================================ * Interactive Tor Interpreter The control interpreter is a new method for interacting with Tor's control interface that combines an interactive python interpreter with raw access similar to telnet. This adds several usability features, such as... * Irc-style commands like '/help'. * Tab completion for Tor's controller commands. * History scrollback by pressing up/down. * Transparently handles Tor authentication at startup. * Colorized output for improved readability. For a tutorial to get you started see... https://stem.torproject.org/tutorials/down_the_rabbit_hole.html ============================================================ * New connect() Function This release of Stem provides a new, even easier method for establishing controllers. Connecting to Tor can now be as easy as... import sys from stem.connection import connect if __name__ == '__main__': controller = connect() if not controller: sys.exit(1) # unable to get a connection print 'Tor is running version %s' % controller.get_version() controller.close() ============================================================ For a rundown on the myriad of improvements and fixes in this release see... https://stem.torproject.org/change_log.html#version-1-2 Cheers! -Damian

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