- tor-dev - lists.torproject.org

Re: [tor-dev] Doesn't hidden services break RFC 3986?
by Ryan Carboni 14 Aug '17

14 Aug '17

Also: just because it's HTTP/S running over a different network stack, doesn't make it a new scheme. Just because your dinner arrives on a different plate doesn't mean the recipe has changed. :-) --- https://bugzilla.mozilla.org/show_bug.cgi?id=1228457 Tor is a strange sort of sacred cow highly revered leaks much methane But RFC 7686 literally bent over backwards to rewrite multiple standards because Tor was long existing. ".onion" shouldn't be resolved or sent over the internet. Sure, IP multicast had to be implemented, but its relevance to people not replacing analog technologies isn't particularly great, and those are corporations who make billions combined per year. But uh yes. Only the plate changed. But internet standards are very clear on plate specifications. Or rather, "authority" lookup. The dinnerware request protocol is pretty clear on this, with other protocols providing for saran-wrap or foil-wrap encapsulation, with their own provisions for exterior labeling. (or if there was a new way to link to torrent hashes, do you think it should be "torrent://hash/" or "hash.torrent"?) Although, if you guys really want to risk your government funding, I suggest $10,000 bug bounties out of a fund sized large enough to hire a single programmer (assuming there's a risk that you'll have more than a dozen severe bugs). To make things more difficult for the NSA, make it clear that there is no requirement for a cyber arms seller to stay bought by one person. Or propagate a meme that a cyber arms seller could sell the idea of an exploit to another cyber arms seller to write a new exploit for the same bug. Force folks like zerodium to pay twice. or uh "Make the enemy live up to its own book of rules." But who is your enemy?

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Getting started coding on Tor [Re: tor-dev Digest, Vol 79, Issue 4]
by Nick Mathewson 14 Aug '17

14 Aug '17

On Sat, Aug 12, 2017 at 3:02 PM, John kongtcheu <johnkongtcheu(a)gmail.com> wrote: > Hello Tor developers, > > I am interested in becoming an open source contributor for Tor, but I > don't know where to start some guidance would be appreciated. > > Thank you, > Hi! We have some introductory material over here, including a list of subprojects and what they're implemented in: https://www.torproject.org/getinvolved/volunteer If you're interested in Tor itself, have a look at the doc/HACKING/GettingStarted.md file in the Tor git repository. It's got a bunch of other useful links. cheers, -- Nick

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Doesn't hidden services break RFC 3986?
by Ryan Carboni 14 Aug '17

14 Aug '17

https://tools.ietf.org/html/rfc3986#section-3 By placing the scheme within the authority as a tld while using the same authority as the HTTP specification, this probably breaks RFC 3986 and maybe others. I might be a bit late in saying this.

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Help us build Tails reproducibly
by u 09 Aug '17

09 Aug '17

Dear Tails and Tor contributors, dear Reproducible Builds community, As you might know, Tails [1] has received the Mozilla Open Source Software award (MOSS) to make Tails ISO images build reproducibly. Since this project has started, less than a year ago, we've made huge progress and we've finally seen some ISO images build reproducibly on the build environments of our core developers as well as on our isobuilder machines. (See our previous reports [2]). However, there are still some remaining issues which we'd like to know more about in order to fix them. That's why we are asking for your help: Please try and build the Tails 3.1 ISO image and report your findings back to us. You will find all instructions for doing so hereafter. Please don't hesitate to contact us if you get stuck at some point in the process, for example by connecting to our chatroom [3]. You can also send us email to tails-dev(a)boum.org (public) or tails(a)boum.org (private). # How? For your convenience all instructions needed to attempt to reproduce Tails 3.1 are included hereafter. However all commands are adapted for Debian Stretch (and Buster/Sid), so your results may vary if you run another Linux distribution. Our full build instructions [4] might help if you are having problems. ## Setup the build environment Building Tails requires the KVM virtual machine hypervisor to be available, a minimum of 1 GiB of free RAM and a maximum of 20 GB of free storage. ### Install dependencies sudo apt-get install \ git \ rake \ libvirt-daemon-system \ dnsmasq-base \ ebtables \ qemu-system-x86 \ qemu-utils \ vagrant \ vagrant-libvirt \ vmdebootstrap && \ sudo systemctl restart libvirtd ### If building as a non-root user (Skip this section if you intend to build Tails as the root user!) Make sure that the user that is supposed to initiate the build is part of the relevant groups: for group in kvm libvirt libvirt-qemu; do sudo adduser $user $group; done Then run `newgrp` (or just reboot) to apply the new group memberships to the session. ## Build Tails 3.1 git clone https://git-tails.immerda.ch/tails cd tails git checkout 3.1 git submodule update --init rake build # Send us feedback! No matter how your build attempt turned out we are interested in you sending us feedback. For that we'll first need some information of the system you used -- please run these commands in the exact same terminal session that you ran `rake build` in (e.g. run them right after `rake build`)! sudo apt install apt-show-versions || : ( for f in /etc/issue /proc/cpuinfo do echo "--- File: ${f} ---" cat "${f}" echo done for c in free locale env 'uname -a' '/usr/sbin/libvirtd --version' \ 'qemu-system-x86_64 --version' 'vagrant --version' do echo "--- Command: ${c} ---" eval "${c}" echo done if which apt-show-versions >/dev/null then echo '--- APT package versions ---' apt-show-versions qemu:amd64 linux-image-amd64:amd64 vagrant \ libvirt0:amd64 fi ) | bzip2 > system-info.txt.bz2 Please have a look at the generated file with bzless system-info.txt.bz2 to make sure it doesn't contain any sensitive information you do not want to leak in case you send this file to us or make it public! Next, please follow the instructions below that match your situation! ## If the build failed. Please open a ticket on our bug tracker [5] with "Category" set to "Build system" and `system-info.txt.bz2` attached (note that this makes this file public). ## If the build succeeded ... Please compute the SHA-512 checksum of the resulting ISO image: sha512sum tails-amd64-3.1.iso and compare it to: 843427fa13446c4b7134a10d3269b693317bbb898759e9d4e5dd8a25583372bed767e575974f5ca0229f1b44a99d4c7b64872c3dc433c0caf8965961cac9fb30 ### Use the SHA256sum from our signed upgrade files instead This is optional, but if you want to use an authenticated checksum, you can find the sha256 checksum in our upgrade files: https://tails.boum.org/upgrade/v1/Tails/3.0.1/amd64/stable/upgrades.yml .. which are signed by the Tails signing key [7]: https://tails.boum.org/upgrade/v1/Tails/3.0.1/amd64/stable/upgrades.yml.pgp The SHA256 checksum should be: 0ef1c7d880308ee9f98c255b2658b75445cc84622eae2944a342dcc50cea71c7 ### ... and the checksums match (i.e. reproduction succeeded). Congrats for successfully reproducing Tails 3.1! Please send an email to tails-dev(a)boum.org (public) or tails(a)boum.org (private) with the subject "Reproduction of Tails 3.1 successful" and attach `system-info.txt.bz2` to it. ### ... and the checksums differ (i.e. reproduction failed). Now you are in a great position to help Tails improve its reproducibility! Please install `diffoscope` [8] version 83 or higher. If you run Debian Stretch, that is: echo 'deb http://ftp.debian.org/debian stretch-backports main' \ | sudo tee /etc/apt/sources.list.d/stretch-backports.list && \ sudo apt update && \ sudo apt -o APT::Install-Suggests="true" \ -o APT::Install-Recommends="true" \ install diffoscope Then download the official Tails 3.1 ISO image [6] and compare it to yours: diffoscope \ --text diffoscope.txt \ --html diffoscope.html \ --max-report-size 262144000 \ --max-diff-block-lines 10000 \ --max-diff-input-lines 10000000 \ path/to/official/tails-amd64-3.1.iso \ path/to/your/tails-amd64-3.1.iso && \ bzip2 diffoscope.* Please send an email to tails-dev(a)boum.org (public) or tails(a)boum.org (private) with the subject "Reproduction of Tails 3.1 failed" and attach `system-info.txt.bz2` to it. We also want you attach one (the smallest!) of diffoscope.txt.bz2 and diffoscope.html.bz2 to the email, but if they are "big" (say >100 KiB) then please don't bomb our mail inboxes! Instead upload the file to some web-based file-sharing service (we'd recommend RiseUp [9]) and include the link(s) in the email. Thank you very much for your interest and help! Cheers! The Tails project [1] http://tails.boum.org [2] https://tails.boum.org/news/report_2017_06/, https://tails.boum.org/news/report_2017_05/, https://mailman.boum.org/pipermail/tails-dev/2017-March/011297.html [3] https://tails.boum.org/support/#talk [4] https://tails.boum.org/contribute/build [5] https://labs.riseup.net/code/projects/tails/issues/new [6] http://dl.amnesia.boum.org/tails/stable/tails-amd64-3.1/tails-amd64-3.1.iso [7] https://tails.boum.org/news/signing_key_transition/ [8] https://diffoscope.org/ [9] https://share.riseup.net/

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[release] Onionoo 4.0-1.3.0
by iwakeh 08 Aug '17

08 Aug '17

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Hi there! Another release of Onionoo is available: https://dist.torproject.org/onionoo/4.0-1.3.0/ This release is a maintenance release: * It adapts to use the improvements of metrics-lib 2.0.0 and * Debian Stretch dependencies and * steps up to Jetty9. (See the changelog [0] and git repo for details.) Please direct comments and questions to the metrics-team mailing list [1]. Cheers, iwakeh [0] https://gitweb.torproject.org/onionoo.git/tree/CHANGELOG.md?h=onionoo-4.0-1… [1] https://lists.torproject.org/cgi-bin/mailman/listinfo/metrics-team -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQIcBAEBCAAGBQJZiYO/AAoJEPeEx9Sa/gviYUQP/jTj8Tp5AtHacrW1zu9GqUry SlOSmwx0EgldVZDc96RD2rz0sef5OR0WBA/kQz8QUL3m6LpjdCmsOz9HyOZNtpqO gEY9RWEm0dfXLMai2BZVApp52X45MwRh+LBP/PTI/Sl5RJ4drmaDr+DZGHAzPJUz uXV9f45LNy/fZgtrR+Cjkr3pr+sb5IB/uGdjJYYC4hXXIhFHe6eRW0mqLGkjl733 sy5Z02ldTKntjeBfu+iVDgtObrYrDkDvbJYyQHPHwPLiVqtKiGZixeK8ojjPimIz 5O/GHH/2m00Jst+u4uyIeUQiUexzv/uMRLKYi0lPshbId1icGpAhs2VHy0pI7CXJ vr6rXkFv07tw86F36kOg2Vvy1/8oy0JEbZPA8hpl1F5tELp5Go0tf8Eq3PahMKh9 DfjOatQdj/BCi6G3dvtCiKyWnwd3chF1Gaqe1GmrAuDnrGGtbAWWv0ofStMOO+7X 2aI4y5Q2QTT7v9UJjks/rw4GOhEq+vlQHUFTVc4vSBm6bxSrowRyIy0/jUzeGs7A XT0CnTWyO5xtuNhGYsZPSx7fENGko1tPOnzjxurHCYcZNM7oBIJKwn2yol+xpEwr 2DE5lyp/8bmb4Ya6/m3li34ku++Y7peXQ3wVagB5aPq1oROZ5ttabi9gA+xPRCqk keSUDKXP9PBz+EtGvMoQ =ELXu -----END PGP SIGNATURE-----

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Various Tor keys, their formats, and usages [was: Bridge Bandwidth Scanner Internship]
by isis agora lovecruft 08 Aug '17

08 Aug '17

Hello! The following was my attempt last week to summarise all of our various keys in server descriptors, how they are formatted, and what they are used for, in the hopes that this is useful in alleviating possible future confusions for others. Let me know (and, more importantly! let Jake know since he's writing a Rust parser for bridge descriptors as part of the Bridge Bandwidth Scanner project) if I got anything wrong. :) ----- Forwarded message from isis agora lovecruft <isis(a)torproject.org> ----- > From: isis agora lovecruft <isis(a)torproject.org> > Subject: Re: Bridge Bandwidth Scanner Internship > Date: Thu, 27 Jul 2017 19:52:47 +0000 > Message-ID: <20170727195247.GI24882(a)patternsinthevoid.net> > To: jnz(a)riseup.net > Reply-To: isis(a)torproject.org > Delivered-To: <isis+torproject(a)patternsinthevoid.net> > > jnz(a)riseup.net transcribed 1.4K bytes: > > Hey Isis, > > > > I have started the sanitization spec and the parser. A lot of the stuff > > I had to learn for the two overlaps, so I am working on them > > simultaneously. Conceptually, I understand the sanitization process, but > > I am a little bit confused about what some of the fields are in the > > descriptors. > > > > Q1. What exactly is the difference between "master-key", "identity-key", > > and "signing-key"? > > > > After reading through the descriptor spec, cert spec, and other docs, I > > am pretty confused on what each of the above means.I'm using the Nom > > crate for the parser, I've never used it before but so far I'm really > > liking it. Have you ever used it? > > This is specified (not all that well, imho) in dir-spec.txt… it's really > confusing. > > For versions of tor new enough to have prop#220 and prop#228 (>0.2.7.2-alpha): > > - "identity-ed25519" is a certificate containing a base64-encoded ed25519 > key. The bridge uses this to authenticate to clients. > > - "master-key-ed25519" is the ed25519 key which is in the > "identity-ed25519" certificate. > > - "onion-key" is an RSA-1024 key, encoded as a PKCS#1 RSAPublicKey > structure, encoded in base64, and wrapped in "-----BEGIN RSA PUBLIC > KEY-----" and "-----END RSA PUBLIC KEY-----". This key is used to > encrypt CREATE cells to in the older TAP handshake protocol. (TAP is > almost entirely unused on the network, last I checked. We'll likely be > removing "onion-key"s in the next year or so, after we EOL some old tor > versions.) > > - "ntor-onion-key" is a public curve25519 key, base64-encoded. This is used > in the newer NTor handshake protocol, which replaced TAP. It is still > quite common to see routers which have both an "onion-key" and an > "ntor-onion-key". > > - "signing-key" is the same type and format as "onion-key" above, but it's > used as a long-term identity key, for authenticating the bridge to > clients. (Similar to "identity-ed25519" just with RSA signatures.) > > - "router-sig-ed255519" is a only present iff "identity-ed25519" is > present, and it's an ed25519 signature of a SHA-256 digest of the > "entire" descriptor (Minus the "@purpose bridge" header since the Bridge > Authority is the one who adds that. So from "router " on the first line > up to and including the first space after "router-sig-ed25519".) This > "entire" descriptor is first prefixed with the string "Tor router > descriptor signature v1" before hashing and signing. After the signature > is produced, it is encoded in base64 and the trailing "="s are removed. > > - "router-signature" contains a signature of the PKCS#1-padded SHA-1 digest > of the "entire" server descriptor, taken from the beginning of the > "router" line (skipping "@purpose bridge" again), through (and > including) the newline after the "router-signature" line. The signature > is made with the router's "signing-key" (a.k.a. identity key). > > For older tor versions (without prop220 and/or prop228): > > - They will have "onion-key", "ntor-onion-key", "signing-key", and > "router-signature", as above. > > I've attached a tarball of today's descriptors for this bridge from the > public/default bridges in Tor Browser: > > https://atlas.torproject.org/#details/FEC8FB380DABA9D3C80790B634E4540BF5D09… > > Let me know if you want some more examples! I only grabbed one because they > are pretty annoying to pull out of the giant, unordered, undeduplicated > files the BridgeAuth produces (at least without writing a full parser). > > Also lmk if you have more questions, the entangled ball of crypto junk we > shove into descriptors is pretty confusing. […snip…] ----- End forwarded message ----- Best regards, -- ♥Ⓐ isis agora lovecruft _________________________________________________________ OpenPGP: 4096R/0A6A58A14B5946ABDE18E207A3ADB67A2CDB8B35 Current Keys: https://fyb.patternsinthevoid.net/isis.txt

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X25519 ←→ Ed25519 key conversions and specs [was: Bridge Bandwidth Scanner Internship]
by isis agora lovecruft 08 Aug '17

08 Aug '17

jnz(a)riseup.net transcribed 2.0K bytes: > Hey Isis, > > I have a few crypto questions for you. The bonus question is purely out > of interest (I searched for the answer, but didn't get a > good/understandable answer, if you are busy don't worry about it). Hey Jake! I'm CCing the conversation to tor-dev, since these are all really good questions. (Also you found another problem in our specs!) > Q1. What does the bit argument in the the ntor-onion-key-crosscert field > do? > > The following is an example ntor-onion-key-crosscert field. The bit > argument is the "1" following ntor-onion-key-crosscert keyword. > > > ntor-onion-key-crosscert 1 > > -----BEGIN ED25519 CERT----- > > AQoABl2EAdjttTuvK9jQzdyi+Mh46ky1Jk9+Hw+FJ6eos5zUxcBDAJF+TGU6oZij > > DOToeg+/lIaEkv0RwIrl5aJta/jf2EdTgHRfCsMOLEWMfqjOA6pmkwc3jnWvWNms > > 7NVBzUcMWgA= > > -----END ED25519 CERT----- > > Q2. The following sentence is the bit argument's documentation from the > dir-spec. Could you possibly explain to me what this means? What is a > public key's "sign"? > > > Bit must be "0" or "1". It indicates the sign of the ed25519 public key corresponding to the ntor onion key. > > The following paragraph is also in the dir-spec, I know that it is > relevant, but I don't understand what it means. > > > C. Converting a curve25519 public key to an ed25519 public key > > > > Given a curve25519 x-coordinate (u), we can get the y coordinate > > of the ed25519 key using > > > > y = (u-1)/(u+1) > > > > and then we can apply the usual ed25519 point decompression > > algorithm to find the x coordinate of the ed25519 point to check > > signatures with. > > > > Note that we need the sign of the X coordinate to do this > > operation; otherwise, we'll have two possible X coordinates that > > might have correspond to the key. Therefore, we need the 'sign' > > of the X coordinate, as used by the ed25519 key expansion > > algorithm. > > > > To get the sign, the easiest way is to take the same private key, > > feed it to the ed25519 public key generation algorithm, and see > > what the sign is. > > BONUS. What is the difference between a curve25519 public key and an > ed25519 public key? Why would you want to convert back and forth between > the two? Okay, this is going to be a long answer. Let me know if parts don't make sense. So, as you noted, dir-spec.txt says [0]: > Bit must be "0" or "1". It indicates the sign of the ed25519 > public key corresponding to the ntor onion key. > > To compute the ed25519 public key corresponding to a > curve25519 key, see appendix C. There are a few different representations of the curve over the Galois field GF(2²⁵⁵ - 19) called curve25519. The (arguably) most useful is the twisted Edwards form of the curve (see our Rust documentation [1] for further details on point forms and more literature) defined for affine points P = (x,y) by the equation -x²+y² = 1 + dx²y² (1) where d = - 121665/121666 This is due to the fact that efficient, complete formulae (meaning that the same formulae, e.g. for point addition, can be used for all points, so you don't have messy if/then statements to deal with exceptional points) exist for Edwards curves. (Recently, complete formulae for Weierstrass curves and other prime-order curves have also been described. [2] However, they are still slightly less-efficient for most tasks.) There's a useful technique called a Montgomery ladder, which is an approach to constant-time (if implemented in a sane manner) point multiplication (i.e. computing nP by taking the point P and adding it to itself n times). This is particularly useful for elliptic curve Diffie-Hellman (ECDH) implementations, but it requires first converting a point from a certain representation (a.k.a. within a specific spatial coordinate system), usually "extended homogeneous twisted Edwards coordinates" (see Hişil's thesis [3], which is the explanation of all the different forms and group laws), into the affine point Q = (u,v) as it would lie on the Montgomery form of the curve: bv² = u³ + au² + u (2) where a = 486662 b = 1 The conversion is rather straighforward, as you can see from mine and Henry de Valence's code [4], but there's a problem in that the compressed form (i.e. "give me the serialised version that is just an array of 32 bytes") of points on the Montgomery curve are just the u-coordinate. You can use this u-coordinate to recover the v-coordinate, [5] and then use both u and v to recover the original Edwards x-coordinate, [6] but there's two possible x-coordinates, one positive and one negative. So, if you want to be able to use a key for both purposes, then, when using Montgomery form (e.g. an X25519 key a.k.a. a "curve25519 key") then you have to also pass around the sign of x. It's kind of icky. In this case, the "ntor-onion-key-crosscert" is an Ed25519 signature (so the public key is a point in twisted Edwards form) of the relay's public master identity key, computed using the "ntor-onion-key" (which is an X25519 key, so a point in Montgomery form). The verifier knows the "ntor-onion-key", but needs to know the sign of x in order to be able to convert it into the Edwards-form public key to check this signature. Following through the code tor is using, it appears that if "Bit" is "0", then x will be positive. If "Bit" is "1" then x will be negative. Tor's behaviour w.r.t. the sign bit (using either curve25519-donna [7] or ref10 [8]) appears to be identical to other implementations, namely Open Whispersystems' code [9] and curve25519-dalek. [10] It appears it isn't specified anywhere what the "Bit" is supposed to mean in terms of parsing the ntor-onion-cert into an Ed25519 key though. :( I made an attempt at specifying it better. [11] As for the question of why one would want to convert back and forth between the two… normally, you wouldn't want to do this. There's nothing concretely horribly wrong or insecure about it, but there are plenty of more theoretical concerns regarding any type of key reuse for different protocols, primarily because it removes any sense of domain separation, such that an attack on one protocol might be assisted by or contribute to attacking the other. With separate keys for separate purposes, you can breathe a lot easier knowing that if, e.g. your ECDH keys were compromised, that your signing key (being a totally different key) is (probably) unaffected. The only time where is does make sense to share a key between two protocols is what Nick's design for the cross-certifications, i.e.: a) Prove that you control the private part of an encryption key by converting it to a signing key, then signing the public master identity key, and b) Authenticate the signature by using the master identity key to sign the entire document (including the other signature). > Thanks for all the help, I hope that you are having a nice day and... > Happy Hacking. > > - Jake No worries! Thanks for the excellent questions and catching more bugs in our specs! [0]: https://gitweb.torproject.org/torspec.git/tree/dir-spec.txt?id=ce09d266#n536 [1]: https://docs.rs/curve25519-dalek/0.10.0/curve25519_dalek/curve/index.html [2]: https://ellipticnews.wordpress.com/2016/05/30/complete-group-laws-for-prime… [3]: https://github.com/isislovecruft/library--/blob/master/cryptography%20%26%2… [4]: https://github.com/isislovecruft/curve25519-dalek/blob/f2883028d/src/curve.… [5]: https://github.com/isislovecruft/curve25519-dalek/blob/f2883028d/src/curve.… [6]: https://github.com/isislovecruft/curve25519-dalek/blob/f2883028d/src/curve.… [7]: https://gitweb.torproject.org/tor.git/tree/src/ext/ed25519/donna/ed25519_to… [8]: https://gitweb.torproject.org/tor.git/tree/src/ext/ed25519/ref10/keyconv.c?… [9]: https://github.com/WhisperSystems/curve25519-java/blob/master/android/jni/e… [10]: https://github.com/isislovecruft/curve25519-dalek/blob/f2883028d/src/curve.… [11]: https://gitweb.torproject.org/torspec.git/commit/?id=2395f34affbe97c19d7bb9… Best, -- ♥Ⓐ isis agora lovecruft _________________________________________________________ OpenPGP: 4096R/0A6A58A14B5946ABDE18E207A3ADB67A2CDB8B35 Current Keys: https://fyb.patternsinthevoid.net/isis.txt

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Need help on my new work related to TOR Project
by Nima Azizzadeh 25 Jul '17

25 Jul '17

Hello My name is Nima Azizzadeh and I'm a second year of mastering Cyber Security major at University of Tehran, Iran. I am extremely interested in pursuing independent research. An extensive research experience will greatly help me consolidate my future career choice. Recently I'm interested in tor project vulnerabilities and I looked at some papers about it. This paper "The Effect of DNS on Tor’s Anonymity, NDSS, February 2017" attracted a great deal of my attention. A lot of research has gone into improving the Tor network, but its use of DNS has received little attention. In this research project, they set out to learn how DNS can harm the anonymity of Tor users, and how adversaries can leverage the DNS protocol to deanonymize users. They studied (i) how exposed the DNS protocol is compared to web traffic, (ii) how Tor exit relays are configured to use DNS, (iii) how existing website fingerprinting attacks can be enhanced with DNS, and (iv) how effective these enhanced website fingerprinting attacks are at Internet-scale. Also, I found another project that I think can defend against these attacks to some degree. The project is T-DNS (Connection-Oriented DNS to Improve Privacy and Security - DNS over TCP and TLS). It combines TCP to smoothly support large payloads and mitigate spoofing and amplification for DoS. T-DNS uses transport-layer security (TLS) to provide privacy from users to their DNS resolvers and optionally to authoritative servers. I want to integrate T-DNS server proxy and client proxy with Tor project source code to add some security feature to Tor project. I also implement T-DNS server proxy and client proxy I just need to add this feature in Tor source code. Something like creating a built-in standalone T-DNS client proxy and server proxy in Tor relays, and encourage people to use them with Tor Exits (and other DNS clients and servers). As you have a lot of exprience on Tor project, I would be happy if you could help me on this or give me some suggestion to clarify the way for me. I look forward to hearing from you! Best Regards, Nima Azizzadeh

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prop224: Deprecating SHA1 circuit digests
by teor 24 Jul '17

24 Jul '17

Hi all, At the moment, Tor uses SHA1 for the running digests of circuit cell payloads. Some of the prop224 code seems to use SHA256 for the digests for client to service rendezvous circuits. But that's not in the spec yet (see #22995 at [0]). How and when do we plan to move away from using SHA1 in Tor circuits? For non-onion service circuits, this would mean: * implementing support for SHA256 [1] circuit digests * adding a Relay protocol version 3 * teaching clients to use SHA256 digests with relays with Relay protocol >= 3 For onion service circuits, it's more complicated, because the following circuit types can't use relay versions from the consensus: * client to intro * service to rend * client to service (Using relay versions from the consensus leaks which consensus clients and services have, which reduces the anonymity set.) Here are the upgrade mechanisms in prop224 at the moment, for both circuit protocol versions and any necessary handshake material: client to intro: * the protocol version could be in a proto line to each intro point, but this isn't implemented yet * the handshake data can be in the link-specifiers (I think?) service to rend * the protocol version could be in the EXT_FIELD in the INTRODUCE cell, but this isn't implemented yet * the handshake data can be in the link-specifiers (I think?) client to service: * the protocol version is in the create2-formats in the descriptor * the handshake data is in HANDSHAKE_INFO in the RENDEZVOUS cells * SHA256 digests are implemented, but not documented in prop224 [0] I suggest we make the following changes to prop224 to make this happen: Protocol version information: * add the relevant relay protocol versions to the intro point section of the descriptor * put the relevant relay protocol versions in an EXT_FIELD in the INTRODUCE cell * check create2-formats contains all the version info we will need to change the client to service circuit protocol version Downgrade resistance: * teach clients and services to use the highest common protocol between client/service and relay, excluding protocols that are below the minimum required protocol versions * work out how we will tell clients to no longer accept an old create2-formats line from a service [0]: https://trac.torproject.org/projects/tor/ticket/22995 [1]: By SHA256, I mean "a good secure hash at the time" T -- Tim Wilson-Brown (teor) teor2345 at gmail dot com PGP C855 6CED 5D90 A0C5 29F6 4D43 450C BA7F 968F 094B ricochet:ekmygaiu4rzgsk6n xmpp: teor at torproject dot org ------------------------------------------------------------------------

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Thoughts on the Counter-RAPTOR paper
by Roger Dingledine 20 Jul '17

20 Jul '17

Hi Prateek, Yixin, (and please involve your other authors as you like), (I'm including tor-dev here too so other Tor people can follow along, and maybe even get involved in the research or the discussion.) I looked through "Counter-RAPTOR: Safeguarding Tor Against Active Routing Attacks": https://arxiv.org/abs/1704.00843 For the tl;dr for others here, the paper: a) comes up with metrics for how to measure resilience of Tor relays to BGP hijacking attacks, and then does the measurements; b) describes a way that clients can choose their guards to be less vulnerable to BGP hijacks, while also considering performance and anonymity loss when guard choice is influenced by client location; and c) builds a monitoring system that takes live BGP feeds and looks for routing table anomalies that could be hijack attempts. Here are some hopefully useful thoughts: ----------------------------------------------------------------------- 0) Since I opted to write these thoughts in public, I should put a little note here in case any journalists run across it and wonder. Yay research! We love research on Tor -- in fact, research like this is the reason Tor is so strong. For many more details about our perspective on Tor research papers, see https://blog.torproject.org/blog/tor-heart-pets-and-privacy-research-commun… ----------------------------------------------------------------------- 1a) The "live BGP feed anomaly detection" part sounds really interesting, since in theory we could start using it really soon now. Have you continued to run it since you wrote the paper? Have you done any more recent analysis on its false positive rate since then? I guess one of the real challenges here is that since most of the alerts are false positives, we really need a routing expert to be able to look at each alert and assess whether we should be worried about it. How hard is it to locate such an expert? Is there even such a thing as an expert in all routing tables, or do we need expertise in "what that part of the network is supposed to look like", which doesn't easily scale to the whole Internet? Or maybe said another way, how much headway can we make on automating the analysis, to make the frequency of alerts manageable? I ask because it's really easy to write a tool that sends a bunch of warnings, and if some of them are false positives, or heck even if they're not but we don't know how to assess how bad they really are, then all we've done is make yet another automated emailer. (We've made a set of these already, to e.g. notice when relays change their identity key a lot: https://gitweb.torproject.org/doctor.git/tree/ but often nobody can figure out whether such an anomaly is really an attack or what, so it's a constant struggle to keep the volume low enough that people don't just ignore the mails.) The big picture question is: what steps remain from what you have now to something that we can actually use? 1b) How does your live-BGP-feed-anomaly-detector compare (either in design, or in closeness to actually being usable ;) to the one Micah Sherr was working on from their PETS 2016 paper? https://security.cs.georgetown.edu/~msherr/reviewed_abstracts.html#tor-data… 1c) Your paper suggests that an alert from a potential hijack attempt could make clients abandon the guard for a while, to keep clients safe from hijack attempts. What about second-order effects of such a design, where the attacker's *goal* is to get clients to abandon a guard, so they add some sketchy routes somewhere to trigger an alert? Specifically, how much easier is it to add sketchy routes that make it look like somebody is attempting an attack, compared to actually succeeding at hijacking traffic? I guess a related question (sorry for my BGP naivete) is: if we're worried about false positives in the alerts, how much authentication and/or attribution is there for sketchy routing table entries in general? Can some jerk drive up our false positive rate, by adding scary entries here and there, in a way that's sustainable? Or heck, can some jerk DDoS parts of the Internet in a way that induces routing table changes that we think look sketchy? These are not reasons to not take the first steps in the arms race, but it's good to know what the later steps might be. ----------------------------------------------------------------------- 2a) Re changing guard selection, you should check out proposal 271, which resulted in the new guard-spec.txt as of Tor 0.3.0.x: https://gitweb.torproject.org/torspec.git/tree/guard-spec.txt I don't fully understand it yet (so many things!), but I bet any future guard selection change proposal should be relative to this design. 2b) Your guard selection algorithm makes the assumption that relays with the Guard flag are the only ones worth choosing from, and then describes a way to choose from among them with different weightings. But you could take a step back, and decide that resilience to BGP hijack should be one of the factors for whether a relay gets the Guard flag in the first place. It sounded from your analysis like some ASes, like OVH, are simply bad news for (nearly) all Tor clients. Your proposed guard selection strategy reduced, but did not eliminate, the chances that clients would get screwed by picking one of these OVH relays. And the tradeoff was that by only reducing the chances, you left the performance changes not as extreme as you might have otherwise. How much of the scariness of a relay is a function of the location of the particular client who is considering using it, and how much is a function of the average (expected) locations of clients? That is, can we identify relays that are likely to be bad news for many different clients, and downplay their weights (or withhold the Guard flag) for everybody? The advantage of making the same decision for all clients is that you can get rid of the "what does guard choice tell you about the client" anonymity question, which is a big win if the rest of the effects aren't too bad. Which leads me to the next topic: ----------------------------------------------------------------------- 3) I think you're right that when analyzing a new path selection strategy, there are three big things to investigate: a) Does the new behavior adequately accomplish the goal that made you want a new path selection strategy (in this case resilience to BGP attacks)? b) What does the new behavior do to anonymity, both in terms of the global effect (e.g. by flattening the selection weights or by concentrating traffic in fewer relays or on fewer networks) and on the individual epistemic side (e.g. by leaking information about the user because of behavior that is a function of sensitive user details)? c) What are the expected changes to performance, and are there particular scenarios (like high load or low load) that have higher or lower impact? I confess that I don't really buy your analysis for 'b' or 'c' in this paper. Average change in entropy doesn't tell me whether particular user populations are especially impacted, and a tiny Shadow simulation with one particular network load and client behavior doesn't tell me whether things will or won't get much worse under other network loads or other client behavior. I can't really fault this paper though, because the structure of an academic research paper means you can only do so much in one paper, and you did a bunch of other interesting things instead. We, the Tor research community, really need better tools for reasoning about the interaction between anonymity and performance. In fact, there sure have been a lot of Tor path selection papers over the past decade which each invent their own ad hoc analysis approach for showing that their proposed change doesn't impact anonymity or performance "too much". Is it time for a Systemization of Knowledge paper on this area -- with the goal of coming up with best practices that future papers can use to provide more convincing analysis? --Roger

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