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Attentive Otter: Analysis of libpurple
by Thijs Alkemade 07 Oct '13

07 Oct '13

Hello! Here is the analysis of libpurple/Pidgin as a candidate for the Attentive Otter project, written by DrWhax and me. Best regards, Thijs (xnyhps) ----- ## Intro Pidgin is an IM client written in C using a GTK+ UI. libpurple is the library used by Pidgin as an abstraction for the different network protocols Pidgin supports. libpurple comes with a number of plugins ("prpls") for the various chat networks it supports. Other UIs using libpurple include Adium (Cocoa), Finch (GNT) and Quail (Qt, in development). ## Release a secure, portable chat program ### Secure Number of security advisories published on https://pidgin.im/news/security/ since 2005-06-10: * libpurple: 6 * nss plugin: 1 * Pidgin: 3 * prpl-gg: 1 * prpl-irc: 2 * prpl-jabber: 7 * prpl-msn: 15 * prpl-mxit: 3 * prpl-oscar (AIM/ICQ): 6 * prpl-qq: (no longer supported) 1 * prpl-sametime: 1 * prpl-silc: 2 * prpl-yahoo: 3 My (xnyhps) personal experience is that the Pidgin developers take reported security issues very seriously and often come up with a fix quickly. However, it does sometimes take a while before they release and deploy that fix. I don't have enough experience with Pidgin (the GTK+ UI) to judge its code quality, but I think the quality of libpurple itself is decent. The quality of prpls varies a lot, generally the reverse-engineered protocols are in worse shape than those with open specifications. I think MSN is definitely the worst and auditing it would take more time than the servers will be online for (until March 2014). I think auditing jabber+irc should be doable and would be a good start: IRC is quite small (>5kloc), XMPP (28kloc) has clear specifications and by using UTF-8 and XML it removes a lot of possible buffer overflow and string manipulation vulnerabilities. DrWhax's personal experience is that Pidgin developers don't always take security issues seriously. In the summer of 2012 I spent a night digging with Jake into the source code and DLL's that they ship and we found out that in 2012, they were shipping vulnerable DLL's with the oldest exploit originating from 2006! It took quite some convincing that this is a serious matter and we had to convince(sigh) the Pidgin folks to update all the DLL's to the latest version. In February 2013, Pidgin finally released a security update which fixed 12 security bugs? I would say, if we would want to go forward with releasing a minimal Pidgin, we should only ship with IRC and XMPP support. ### Portable Pidgin provides official instructions on how to run Pidgin from an USB stick: https://developer.pidgin.im/wiki/Using%20Pidgin#RunningWindowsPidginFromaUS…. ## Sends all traffic over Tor libpurple has a proxy setting that will force all traffic to pass through Tor. This disables all SRV lookups, meaning many XMPP servers require manual configuration to work. UPnP (used for automatic port fowarding and external IP detection) can be disabled globally. ## Can be used with a wide variety of chat networks libpurple includes support for: * AIM * Bonjour * Gadu-Gadu * Google Talk * Groupwise * ICQ * IRC * MSN * MXit * MySpaceIM * SILC * SIMPLE * Sametime * XMPP * Yahoo! * Zephyr Though nearly everyone of these is a separate prpl, so would require its own auditing. ## Uses off-the-record encryption of conversations by default The Pidgin-OTR plugin can be configured to enable OTR by default. Including this plugin with Pidgin by default is underway. ## Has an easy-to-use graphical user interface localized into Farsi, French, Spanish, and Arabic. It has a graphical user interface which a large number of users might already be familiar with. From https://developer.pidgin.im/l10n/2.x.y/: * Farsi: 59.77% finished. * French: 98.95% finished. * Spanish: 99.31% finished. * Arabic: 78.02% finished. This breakdown includes all prpls, so might turn out differently when only including a subset of them. ## Cross-platform support Pidgin ships binaries for Windows and Linux. By packaging GTK+, it should be possible to package it to run on OSX too, though the UI would be quite confusing to many OSX users. Another option on OS X is Adium, though this increases the amount of code to be audited by a large factor. ## Integration with Tor libpurple supports plugins written in C, Tcl, Perl and C# (Mono). These can make changes to the preferences to automate configuring it for Tor. It is also possible to configure Pidgin using D-Bus, but for security reasons it is probably wiser to disable D-Bus support. So the options to control Tor are: * A C/Tcl/Perl/C# plugin that launches a Tor process and which sets up Pidgin's preferences accordingly. * Use Tor Launcher from the TBB to start both Tor and Pidgin. Configuring Pidgin could happen by: * Writing to the preference files before starting it. * Communicating the preference changes to a simple C/Tcl/Perl/C# plugin. * D-Bus. (Unlikely to work on Windows and difficult to secure) ## Pidgin 3.0 Pidgin 3.0.x will be released with OTR support by default, which is awesome, only one codebase has to be maintained in the various Linux distributions and Windows clients! Huzzay! Something i'm less happy with, is that the Pidgin developers started using Webkit for HTML rendering within the client. Webkit doesn't have a very good security history and opens up with another giant security hole. If we would want to release Pidgin inside of TIMBB, I would propose to work on Pidgin 3.0 and not the older 2.x releases.

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[rt.torproject.org #14664] Tor on iOS (fwd)
by Veronique Dubois 06 Oct '13

06 Oct '13

---------- Forwarded message ---------- Date: Sat, 5 Oct 2013 23:59:16 +0000 From: Colin Childs via RT <help(a)rt.torproject.org> To: vero(a)was.fm Subject: [rt.torproject.org #14664] Tor on iOS On Sat Oct 05 21:57:29 2013, vero(a)was.fm wrote: > Dear Tor, > > I work with a small group of developers called Wizardry and > Steamworks and we have recently managed to port Tor to Apple iOS devices. > The port requires for iOS to be jailbroken (please note that that action > is not illegal but just //may// void warranty). > > The port has been uploaded to Cydia on BigBoss's repo and can be > found at: > > http://moreinfo.thebigboss.org/moreinfo/depiction.php?file=torDp > > We have seen that your website lists download locations for Tor > at: > > https://www.torproject.org/download/download-easy.html.en > > and that on the page: > > https://www.torproject.org/download/download.html.en > > an Android Bundle is listed under the "Tor for Smartphones" > header. > > We were wondering if you could list our port to iOS or, at > least, mention somewhere on the download page that Tor is now also > available for Apple iOS devices via Cydia. > > Thank you, > Veronique Dubois > on behalf of Wizardry and Steamworks @ was.fm Hello, Please send a copy of this message to our Tor-Dev mailing list at https://lists.torproject.org/cgi-bin/mailman/listinfo/tor-dev. -- Colin C.

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Re: [tor-dev] Tools of Mass Obfuscation or where are my internet curtains?
by Malard Joel 04 Oct '13

04 Oct '13

Ian, Thanks. Tell me what a better forum would be and I' ll gladly move this discussion there. Your suggestion does use encryption if only as a catalyst. There was a time when encrypted content could not be sent to Canada from the US and I can imagine some governments forbidding the use of encryption. Harvesting keywords from k messages of length n takes O(n.k) time and space, possibly with some large constants. If the messages are scrambled hopefully it would take O(k.n.log(n)) time to harvest them. What would really help imho with mass snooping would be a transfer method that requires O(k.log(k).n) time for any form of keyword harvesting. I don' t have an answer, hence the contest. Another approach might be to string every m-th bit of a message of n bits, where m an n are relatively prime, cyclically. Best of luck with Tor. Cheers, Joel ------------------------------ On Thu, Oct 3, 2013 2:58 PM PDT Ian Goldberg wrote: >On Thu, Oct 03, 2013 at 02:34:50PM -0700, Malard Joel wrote: > > > Do you think that the code at https://github.com/malardj/ slice, that uses neither encryption nor a password, could help a community proof their communications from massive systemic eavesdropping by making the latter computationally impractical or financially unsustainable? Do you think that a tool like that would be valuable if it existed? Would you think of some yourself that everyone could use? > > I am unaffiliated with any institution but I would like to setup a contest for the best such algorithm or procedure that does not involve cryptography and that can be implemented by any group of ordinary citizens for the purpose of proofing their Internet communications of ASCII characters from systemic eavesdropping. > > I need help setting up the rules of competition ( i never did this), finding judges (I am totally unqualified), finding (virtual) places where to announce and hold the competition. I would welcome your suggestion on how to make this contest more relevant to all. Can you help, or suggest where to look for help? > > The code above is a quick example of the type of entries that I have in mind. It consists in a C++ program that inputs a character string, slices it and shuffles those slices into a javascript program that displays the input when it is run. The method purports to hamper the work of automated keyword harvesters. The available code does not support html text but that capacity is not be hard to add. > > With best regards, > > Joel Malard, PhD > Fremont, CA > >I don't think this is the right list for this discussion, but how about: > >- Pick a 128-bit random key K >- Encrypt the message using key K with, say, AES-GCM or your favourite > authenticated encryption mode to yield the ciphertext C (including > tag) >- randomize the last b bits of K to yield K', for some b, probably > around 30, but could be anything from 0 to 40ish. >- output K' concatenated with C > >Notably, you don't output b. The receiver just runs a counter X up from >0 until C authenticates using the key (K' XOR X). b controls how long >this will take, but the receiver doesn't know it. (There was a >password-stretching algorithm like that in USENIX Security (I think it >was) a little while ago; the adversary doesn't know how many iterations >to wait before giving up / trying another password.) The high part of K >acts like a salt. > >It's kind of like the old Lotus Notes encryption, in that the NSA got to >know the high part of the key, and just had to brute the low 40 bits, >only now the receiver has to brute it as well. It's not technically >encryption, as there's no shared or public key. But there's also no key >management, of course. > > - Ian >_______________________________________________ >tor-dev mailing list >tor-dev(a)lists.torproject.org >https://lists.torproject.org/cgi-bin/mailman/listinfo/tor-dev

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Tools of Mass Obfuscation or where are my internet curtains?
by Malard Joel 03 Oct '13

03 Oct '13

Do you think that the code at https://github.com/malardj/ slice, that uses neither encryption nor a password, could help a community proof their communications from massive systemic eavesdropping by making the latter computationally impractical or financially unsustainable? Do you think that a tool like that would be valuable if it existed? Would you think of some yourself that everyone could use? I am unaffiliated with any institution but I would like to setup a contest for the best such algorithm or procedure that does not involve cryptography and that can be implemented by any group of ordinary citizens for the purpose of proofing their Internet communications of ASCII characters from systemic eavesdropping. I need help setting up the rules of competition ( i never did this), finding judges (I am totally unqualified), finding (virtual) places where to announce and hold the competition. I would welcome your suggestion on how to make this contest more relevant to all. Can you help, or suggest where to look for help? The code above is a quick example of the type of entries that I have in mind. It consists in a C++ program that inputs a character string, slices it and shuffles those slices into a javascript program that displays the input when it is run. The method purports to hamper the work of automated keyword harvesters. The available code does not support html text but that capacity is not be hard to add. With best regards, Joel Malard, PhD Fremont, CA

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RFC of proposal draft for "Migration to ed25519 HS identity keys and privacy-preserving directory documents"
by George Kadianakis 03 Oct '13

03 Oct '13

Here is another HS proposal draft. This one specifies how to migrate from the current HS protocol to the one specified in proposals "Migrate HS identity keys to Ed25519" and "Stop HS address enumeration by HSDirs": https://lists.torproject.org/pipermail/tor-dev/2013-August/005279.html https://lists.torproject.org/pipermail/tor-dev/2013-August/005280.html (I will soon write a proposal that merges these two proposals into one) This proposal is in serious need for comments. Specifically, see section "1.1. From the PoV of Hidden Services" which I left entirely unspecified. There are also probably multiple migration concerns which I have forgotten or completely ignored. Inlining: Filename: xxx-hs-id-keys-migration.txt Title: Migration to ed25519 HS identity keys and privacy-preserving directory documents Author: George Kadianakis Created: 13 September 2013 Target: 0.2.5.x Status: Draft [More draft than Guinness.] 0. Overview and motivation Proposal XXX introduces two new HS features: a) Stronger HS identity keys. b) New-style HS directory documents so that HS addresses are not leaked to HSDirs. This document specifies how different Tor actors must act after proposal XXX is implemented, so that the migration can proceed smoothly. We aim for the migration to be smooth both from the perspective of Hidden Services (introduce grace period so that HS operators don't wake up one day to find that their HS can't be accessed with that address anymore) and from an implementation perspective (avoid bloating the Tor protocol or introducing sensitive flag days). 1. Migration strategy After proposal XXX is implemented: a) The HS address format will change (called "new-style HS address" in this document) b) New HSDirs will be introduced (called "HSDirV3" in this document) c) New-style HS descriptors will be introduced (called "HS V3 descriptors" in this document). The following sections investigate how these changes influence the various Tor actors: 1.1. From the PoV of Hidden Services: === XXX DISCUSSION XXX === I see (at least) three migration strategies here. I'm not sure which one is better so I'll write all of them and we can then discuss them and pick one. a) After proposal XXX is implemented, Tor (configured as an HS) will only publish HS V3 descriptors by default. There will be a torrc parameter that the HS operator can use, that turns on publishing of HS V2 descriptors for backwards compatibility with the old HS address (the old identity key must be kept around). b) After proposal XXX is implemented, Tor (configured as an HS) will publish both V3 and V2 HS descriptors for each Hidden Service. There will be a torrc parameter that turns off publishing of V2 HS descriptors. This parameter will eventually be switched off by default. c) After proposal XXX is implemented, Tor (configured as an HS) will only publish V3 HS descriptors. The code that publishes V2 descriptors can be disabled or removed. HSes who want to publish V2 descriptors (and keep the same address) will have to maintain two copies of Tor -- one running the latest Tor version, and another one running an older version that supports V2 descriptors. The engineer inside me tells me to go with c), but I feel that it leaves all the burden to the HS operators. I haven't checked how much implementation effort doing a) or b) would take us. 1.2. From the PoV of the HS client: Tor clients can distinguish new-style HS addresses from old ones by their length. Legacy addresses are 16 base32 characters, while new ones are 56 (XXX) base32 characters. If Tor is asked to connect to a legacy address it SHOULD throw a warning and advocate the use of new-style addresses (it should still connect to the HS however). In the future, when old-style HS addresses are close to depletion, we can introduce a torrc parameter that blocks client connections to old-style HS addresses. 1.3. From the PoV of HS directories: Tor relays will advertise themselves as HSDirV3 servers using the "hidden-service-dir" router descriptor line. For a while, relays will also continue being HSDirV2 servers. We will specify a timeout period of X months (4?), after which relays will stop being HSDirV2 servers by default (using the HidServDirectoryV2 torrc parameter). 1.4. From the PoV of directory authorities: Authorities will continue voting for HSDirV2 servers. Eventually, when all relays have upgraded and no one is claiming to be HSDirV2, we can disable and remove the relevant code. XXX Need to specify grace periods. XXX What did I forget?

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[draft] Proposal XXX: On upgrading HS identity keys and on a new HS directory scheme that does not leak
by George Kadianakis 01 Oct '13

01 Oct '13

release early; release often again This is a draft of a proposal that merges the two proposals I posted last month, namely the "Migrate HS identity keys to Ed25519" and "Stop HS address enumeration by HSDirs" proposals. This goes together with the "Migration to ed25519 HS identity keys and privacy-preserving directory documents" I posted two weeks ago. It tried to address most of the comments from Nick and Matthew. There are still lots of stuff to fix (especially the key derivation part). Inlining: Filename: xxx-hs-id-keys-and-onion-leaking.txt Title: On upgrading HS identity keys and on a new HS directory scheme that does not leak Author: George Kadianakis Created: 10 August 2013 Target: 0.2.5.x Status: Draft [More draft than Guiness.] ToC: 0. Overview 1. Motivation 2. Related proposals 3. Overview of changes 4. Specification of changes 5. Discussion 6. Acknowledgments Appendix: A0. Security proof of directory scheme --- 0. Overview: This proposal has two aims: a) Improve the strength of HS identity keys. Specifically, this proposal suggests the adoption of Ed25519 ECDSA keys as a replacement for the RSA-1024 keys that are currently in use by hidden services. b) Stop HS address enumeration by HSDirs When a client asks for the descriptor of a hidden service the hidden service address is leaked to the HSDir that was inquired. This proposal suggests a new directory scheme that prevents HSDirs from learning the hidden service address or the contents of the hidden service descriptors they serve. 1. Motivation The long-term identity keys of Hidden Services are RSA-1024 keys; we consider these weak and in need for replacement. Furthermore, 80-bit hidden service addresses are short enough to be prone to brute-force impersonation attacks. Ed25519 (specifically, Ed25519-SHA-512 as described and specified at http://ed25519.cr.yp.to/) is a good alternative: it's secure, fast, has small keys and small signatures, is bulletproof in several important ways, and supports fast batch verification. (It isn't quite as fast as RSA1024 when it comes to public key operations, since RSA gets to take advantage of small exponents when generating public keys.) 2. Related proposals This proposal goes hand in hand with proposal XXX "On the migration to Ed25519 HS identity keys and privacy-preserving directory documents". Proposal XXX specifies how the schemes described in this proposal should be deployed in the real Tor network to minimize frustration and bad vibes. XXX Another related proposal is proposal XXX "On the upgrade of Hidden Service service keys" which defines the upgrade from the current RSA-1024 HS service keys to a more powerful cryptosystem. 3. Overview of changes This section provides a high-level overview of the changes suggested in this document. 3.0. Overview of identity-key changes Longterm RSA-1024 "identity keys" are used by hidden services to authenticate themselves to clients. This proposal specifies: * The generation of new Ed25519 long-term identity keypairs (#KEYGEN) * A new HS descriptor format (v3) that contains Ed25519 HS identity keys (#NEWDESC) * A way for clients to upload and fetch v3 descriptors from HSDirs (#DESCFETCH and #DESCUPLOAD) 3.1. Overview of anti-enumeration scheme Currently, Hidden Services upload their unencrypted descriptor to hidden service directories (HSDirs). HSDirs store the unencrypted descriptor in an internal map of: <hs address> -> <hs descriptor> When a client wants the descriptor of an HS, it asks an HSDir for the descriptor that corresponds to <hs address>. If the HSDir has such an index in its map, it returns the <hs descriptor> to the client. This proposal asks Hidden Services to periodically derive a new ephemeral keypair from their long-term identity key; the new keypair being a function of the identity key and a time-dependent nonce. The derivation should be one-way; if you know the identity key you should be able to derive the ephemeral key but not the other way around. Finally, a client should be able to derive the ephemeral HS public key from the long-term HS public key without knowing the long-term HS private key (#KEYPAIRDERIVATION) Hidden Services then encrypt their descriptor with a symmetric key (derived from the long-term identity public key) and sign the ciphertext and the ephemeral public key with their ephemeral private key (#NEWDESC). Then they place the ephemeral public key, the encrypted descriptor and the signature in a v3 hidden servide descriptor and send that to the HSDir (#DESCUPLOAD). When the HSDir receives a v3 hidden service descriptor, it validates the signature using the embedded ephemeral public key and if it verifies it stores the descriptor in an internal map of: <ephemeral public key> -> <v3 descriptor> (#DESCHANDLING). Now, out of band, the HS gives to its clients a <z>.onion address. <z> in this case is the long-term public key of the HS (this is different from the current situation where <z> is the hash of the long-term public key). A client that knows the <z>.onion address and wants to acquire the HS descriptor, derives the <ephemeral public key> of the HS using <z> and the same key derivation procedure that the HS uses. She also derives the symmetric key that decrypts the encrypted HS descriptor (#KEYPAIRDERIVATION). The client then contacts the appropriate HSDir and queries it for the descriptor with index <ephemeral public key>. If the HSDir has such an index in its internal map it passes the <v3 descriptor> to the client (#DESCFETCH). The client then verifies the signature of the v3 descriptor, and if it's legit she decrypts the encrypted descriptor using the ephemeral symmetric key. The client now has the Hidden Servide descriptor she was looking for (#DESCHANDLING). 4. Specificaton of changes 4.0 Generation of long-term identity-key Ed25519 keypairs (#KEYGEN) When a hidden service starts up with no Ed25519 identity keys, it generates a new identity keypair. 4.1. Ephemeral keypair derivation (anti-enumreation) (#KEYPAIRDERIVATION) XXX Leaving this unpsecified for now till the security proof comes along. 4.1.0. By Hidden Services: For now, let's assume that after this paragraph each HS has a per-TIME_PERIOD ephemeral keypair. It also has a symmetric key derived from the identity public key to encrypt its descriptor. 4.1.1. By clients: When a Tor client is asked to connect to a hidden service address <z>.onion, it assumes that <z> is the long-term public key of the hidden service. Internally, and without notifying the user, the Tor client generates the ephemeral public key and ephemeral symmetric key of the HS for that time period (using the long-term public key of the hidden service and the procedure specified in the previous section). 4.2. New v3 Hidden Service Descriptor Format (#NEWDESC) To serve the purposes of this proposal we need to perform multiple modifications to hidden service descriptors. Specifically, to migrate to new identity keys we need to change the format of the v2 Hidden Service descriptor to use Ed25519 keys. Furthermore, to provide enumeration protection we need to encrypt the whole descriptor with the ephemeral symmetric key. To do so we define a new construct just for this section, called "intermediate descriptor". It has the same format as a v2 hidden service descriptor but uses Ed25519 instead of RSA-1024. The following changes are performed to the v2 HS descriptor: [*] The "permanent-key" field is replaced by "permanent-key-ed25519": "permanent-key-ed25519" SP an Ed25519 public key [Exactly once] The public key of the hidden service which is required to verify the "descriptor-id" and "signature-ed25519". In base64 format with terminating =s removed. [*] The "service-key" field is replaced by "service-key-ed25519': "service-key-ed25519" SP an Ed25519 public key [Exactly once] The public key used to encrypt messages to the hidden service. In base64 format with terminating =s removed. [*] The "signature" field is replaced by "signature-ed25519': "signature-ed25519" SP signature-string [At end, exactly once] A signature of all fields above using the private Ed25519 key of the hidden service. In base64 format with terminating =s removed. Now we define the format of the new v3 Hidden Service descriptor that is uploaded to the HSDirs: "ephemeral-public-key" SP public-key [At start, exactly once] The ephemeral HS public key for this time period. In base64 format with terminating =s removed. "encrypted-descriptor" SP encrypted-descriptor [Exactly once] An encrypted intermediate descriptor (as specified above). It's encrypted with AES in CTR mode with a random initialization vector of 128 bits that is written in the beginning of the encrypted string. The ephemeral symmetric key derived in section XXX is used as the secret key of AES. The encrypted string is encoded in base64 and surrounded with "-----BEGIN MESSAGE-----" and "-----END MESSAGE-----". "publication-time" SP YYYY-MM-DD HH:MM:SS NL [Exactly once] A timestamp when this descriptor has been created. It should be rounded down to the nearest day. The timestamp SHOULD be used by the clients and HSDirs to discard old descriptors. XXX Should we specify how long the HSDir is supposed to keep the descriptor? rend-spec.txt doesn't do so. XXX Is "rounded down to the nearest day" too extreme of a rounding? Other Tor documents round it down to the nearest hour. Does it matter if our expiration time is longer than a day? XXX Should we kill the "publication-time" in the HS descriptors? Or just leave it there? "signature" SP signature [At end, exactly once] A signature of all fields above using the ephemeral private key of the hidden service. In base64 format with terminating =s removed. 4.3. Uploading v3 HS descriptors to HSDirs (#DESCUPLOAD) A new type of Hidden Service Directory Server must be established which knows how to handle v3 Hidden Service descriptors. The Hidden Service follows the same publishing procedure as for v2 descriptors but instead of sending an HTTP 'POST' to "/tor/rendezvous2/publish", the HS sends the 'POST' request to "/tor/rendezvous3/publish" with the descriptor included in the body of the 'POST'. 4.4. Fetching v3 HS descriptors from HSDirs (#DESCFETCH) When a client needs to fetch a v3 Hidden Service Descriptor from an HSDir, it follows the exact same procedure as for v2 descriptors but instead of sending an HTTP 'GET' to "/tor/rendezvous2/<z>", it sends an HTTP 'GET' to "/tor/rendezvous3/<z>" where <z> is the base32 encoding of the *ephemeral* public key of the Hidden Service. XXX base32 is used because it's URL-safe and because we don't really care about the extra length. XXX example? 4.5. v3 hidden servide descriptor handling (#DESCHANDLING) 4.5.1. By HSDirs: When an HSDir receives a v3 hidden service descriptor, it verifies its signature using the ephemeral public key that was included in the descriptor. If the signature verifies and the descriptor timestamp is reasonable, the descriptor is accepted and cached. Otherwise, the descriptor is discarded. 4.5.2. By clients: When a client receives a v3 hidden service descriptor, it checks the timestamp and verifies the signature using the previously derived keys and discards it if the signature was not proper. If the signature is proper, the client uses the derived ephemeral symmetric key to decrypt the 'encrypted-descriptor' part of the metadescriptor. 5. Discussion [Points here might deserve their own sections] Do we need the HSDir hash ring, even though the HS address and the descriptor are now hidden from HSDirs? An Ed25519 public key is 32 bytes. 32 bytes in base32 encoding is 56 characters (or 52 with the '=' padding removed). Do we want a different URL encoding or are we happy with addresses like: mfrggzdfmztwq2lknnwg23tpobyxe43uov3ho6dzpjaueq2eivda.onion ? 6. Acknowledgments The cryptography behind this proposal was originally proposed by Robert Ransom in a private email thread and subsequently posted in tor-dev [0]. Discussion was continued in trac ticket #8106 [1]. During the past 6 months many bright people have looked at the cryptography behind this scheme. The list of people includes Nadia Heninger, Leonid Reyzin, Nick Hopper, Aggelos Kiayias, Tanja Lange, Dan J. Bernstein and probably others that I can't recall at this point. Thanks! Parts of this proposal has been based on discussions with Nick Mathewson and his proposal 220. XXX "One more: Christian Grothoff told me in Garching that GNUnet does something quite similar for its keys. So we should probably check out their approach too, and include them in the "related work" section of any hypothetical publication here. :)" Appendix: A0. Security proof of directory scheme XXX A security proof of the above scheme is under development. We are not going to implement or deploy anything before we have a solid proof of this.

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Re: [tor-dev] Sponsor F: update; next meeting [in *two weeks*]
by Matt Pagan 01 Oct '13

01 Oct '13

On Mon, 30 Sep 2013 19:13:37 -0700 Tom Lowenthal <me(a)tomlowenthal.com> wrote: > Today, at 1100 Pacific, we spent more than 90 minutes discussing > [Sponsor F][]. Here's the summary. > > **READ THIS**: The next Sponsor F meeting will be held in a mere two > weeks on **2013-10-14, at 1100h Pacific in #tor-dev**. > > This is a schedule change: from now on, the meetings will be every two > weeks. It's possible that we may have to increase this to every week, > depending on how fast we work, and how long meetings are taking. If > you should be at these meetings but cannot make Mondays at 1100h > Pacific, please contact me, and I'll start the process of finding a > better time or times. > > If you are individually in the `cc` field of this message, it's > because I think that there's something which I think you need to do > for Sponsor F before Halloween. You should also come to the next > Sponsor F meeting. If you can't make the meeting, or don't think this > work applies to you, you should get back to me ASAP so we can fix it. > > Is something else missing, wrong, or messed up? I'd like to know. > > [Sponsor F]: > https://trac.torproject.org/projects/tor/wiki/org/sponsors/SponsorF/Year3 > > > * * * * * > > > Core Phase 2 Deliverables > ========================= > > > UDP Transport [#10] > ------------- > > **[On Track: Minimal]** Karsten will work with Rob to complete the > Shadow simulation of this work, then write up a full report on this, > probably with Stephen's help. We expect both tasks to be complete by > Halloween. This likely represents a minimal outcome for this > deliverable. > > > Combine obfuscation (obfsproxy) with address-diversity (flashproxy) > [#11] > ------------------------------------------------------------------- > > **[On Track: Minimal]** The work of integrating obfsproxy with > flashproxy is done. George will include this in the next released > version of the pluggable transports browser bundle. George will also > write a report on this work. Ximin and David will help. By Halloween, > the report will be complete and the bundles will either be released or > well on their way through testing. This likely represents some > combination of minimal or intended outcomes for this deliverable. > > > Bridge Metrics [#12] > -------------- > > **[Done: Intended]** Our reporting code has been merged into master. > It will ride the trains or flow downstream or whatever your favorite > code development cycle imagery is, and show up in future releases. As > it goes through alpha, beta, and release, gets picked up and adopted > by more operators, we'll get more comprehensive sample coverage, and > better data. This likely represents an ideal outcome for this > deliverable. > > > N23 Performance Work [#13] > -------------------- > > **[On Track: Alternate]** Roger doesn't think that N23 is as good as > we thought it was, so he's going to write a report on the various > performance improvements we've implemented lately; the performance > work which we though about, but decided not to implement, and why; and > a wishlist of future performance work and research. He'll have this > done by Halloween. This likely represents an alternate outcome for > this deliverable. > > > Improved Scheduling [#14] > ------------------- > > **[On Track: Intended]** Nick will work with Roger and Andrea to > implement an improved scheduler (possibly based on picking randomly, > weighted by bandwidth), and -- if possible -- also to refactor `cmux`. > If time permits, Nick will also attempt to simulate this using Shadow > , probably with Karsten's help. Finally, Nick will produce a full > report before Halloween. This likely represents an intended outcome > for this deliverable. > > > Alternate `Fast` Flag Allocation [#15] > -------------------------------- > > **[At Risk]** The person who we initially expected to do this work > does not seem to be available to do it. We need to find an alternate > plan to execute this deliverable. If you think you can do it, please > read [ticket #1854][#1854] and get in touch. > > [#1854]: https://trac.torproject.org/projects/tor/ticket/1854 > > > VoIP Support [#16] > ------------ > > **[On Track: alternate]** Our implementation strategy for this was > high-latency send-an-mp3-over-XMPP using Gibberbot/Chatsecure, or a > similar system. The internal milestone was to have a release candidate > available today. Sadly, Nathan (who is on point for this) wasn't on > the call. Fortunately, Nathan [blogged][guardian-1] about Chatsecure's > `12.4.0-beta4` ten days ago, and a tantalizingly-named > [`ChatSecure-v12.4.2-release.apk`][chatsecure-release] > ([sig][chatsecure-release-sig]) is available in the Guardian Project > [release directory][guardian-releases]. The outlook seems good, but > Tom will follow up with Nathan as soon as possible to verify these > outrageous claims. Nathan, if you're reading this, could you get in > touch (email, IRC, XMPP, whatever). Thanks! > > [guardian-1]: > https://guardianproject.info/2013/09/20/gibberbots-chatsecure-makeover-almo… > [chatsecure-release]: > https://guardianproject.info/releases/ChatSecure-v12.4.0-beta4-release.apk > [chatsecure-release-sig]: > https://guardianproject.info/releases/ChatSecure-v12.4.0-beta4-release.apk.… > [guardian-releases]: https://guardianproject.info/releases/ > > > > Extended Phase 2 Deliverables > ============================= > > > VoIP Support [#17] > ------------ > > **[Limbo: Intended]** Here we're talking about getting a general VoIP > client (Mumble) to work over Tor. This discussed in [ticket > #5699][#5699], and [instructions][torify-mumble] for using Mumble over > Tor are on the wiki. We didn't get an update during the meeting, so if > you're working on this, get in touch, eh? > > [#5699]: https://trac.torproject.org/projects/tor/ticket/5699 > [torify-mumble]: > https://trac.torproject.org/projects/tor/wiki/doc/TorifyHOWTO/Mumble > > There still exists a bug in Mumble such that when network connections are routed through a proxy they leak DNS requests. This past month I've been reading QT documentation so that I can understand the Mumble code better and find the bug. After the meeting on IRC, velope suggested that fixing it might be as simple as implementing SOCKS5 with hostname. DNS leaks also occur with HTTP proxies, which shouldn't happen. See also: http://sourceforge.net/p/mumble/bugs/1033/

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Criteria for prioritizing pluggable transport work
by Roger Dingledine 30 Sep '13

30 Sep '13

Below is my first go at a list of criteria to consider when evaluating pluggable transports for readiness of deployment to users. The goal isn't to say that every transport has to "pass" each question -- rather, I'm hoping to fund a researcher-developer at some point soon to polish some of the research prototypes so we can include them in the PT TBB, and I wanted to think about guidelines for how they should prioritize which PTs to work on. What points is it missing? What points does it mis-explain? See also George's "How the pluggable transports factory works" mail: https://lists.torproject.org/pipermail/tor-dev/2013-August/005231.html Thanks! --Roger ---- Section one, how reviewed / reviewable is it: 1) Is the software published, and is it entirely free and open source? Some designs call for non-free (and non-distributable) components like Skype, a copy of Windows in a VM image, etc. 2) Is there a published design document, including a threat model? Is there a specification? How testable are its security / unblockability claims? We should also consider how much peer review the design has received, and whether the project is getting continued attention by its inventors. 3) What is its deployment history? What kind of users did it have and how many? How much publicity? Did it get blocked? Section two, evaluation of design: 4) How difficult or expensive will it be to block the design (by protocol, by endpoints, etc)? For example, what services or protocols does it rely on being usable or reachable? Expense could include actual cost or could include collateral damage. Another way to measure might be the fraction of censoring countries where the technique is expected to work. 5) What anonymity improvements does the design provide, if any? While many pluggable transports focus only on reachability and leave anonymity properties to Tor, some research designs use the pluggable transport interface to experiment with improved traffic analysis resistance, such as by adding padding to defend better against website fingerprinting attacks. 6) What's the bandwidth overhead? Some transports like Obfsproxy don't inflate communication size, while others like Stegotorus wrap their communications in a more innocuous protocol at a cost of sending and receiving more bytes. Designs with higher bandwidth overhead can provide better blocking-resistance, but are also less suited for low-bandwidth environments. 7) Scanning-resistance: how does the design fare against active probing attacks, like China's follow-up connections that test for vanilla Tor traffic? ("How the Great Firewall of China is Blocking Tor", Philipp Winter, FOCI 2012). Section three, evaluation of implementation: 8) Does the implementation use Tor's Pluggable Transport (PT) Application Programming Interface (API) already? Tor has a standard recommended approach so transport modules can be invoked and managed by the Tor process. The PT API also allows Tor to automatically publish capabilities of the transport, collect user and usage statistics from the transport, and so on. 9) Is the implementation cross-platform (Windows, OS X, Linux at least)? How about support for mobile platforms? 10) How easy is the build process, and how easy is deployment and scaling? For example, what software libraries does it require, how likely are we to get enough bridge-side addresses, etc? 11) How is the code from a security and maintainability perspective? Are there unit tests, integration tests, etc? While the underlying Tor channel provides security properties like encryption and authentication, pluggable transports can still introduce new security risks if designed or built improperly.

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Announcing liballium (A C Tor Pluggable Transports Utility Library)
by Yawning Angel 30 Sep '13

30 Sep '13

Hello, For those aspiring Pluggable Transports authors out there, I've recently written a simple library that handles the Tor Pluggable Transport Configuration protocol. The idea is for this library to be the C/C++ equivalent to pyptlib (and maybe more, depending on how much time I have to work on it). The code is available at: https://github.com/Yawning/liballium It still needs more documentation, but all of the use cases are covered by a reasonably well commented example (examples/ptcfg_example.c). Questions, comments, feedback all appreciated. -- Yawning Angel

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HTTPS Server Impersonation
by Rohit 30 Sep '13

30 Sep '13

Hi, I was thinking about proposal #203 (Avoiding censorship by impersonating an HTTPS server) and have a few thoughts. I'm not sure if I've understood how everything fits correctly but here goes: For each bridge, we give their identity fingerprint and a shared secret along with their IP address and port. ie: bridge <ipaddress:port> <fingerprint> <shared_secret> The fingerprint allows the client to verify the identity of the bridge (via signed certificate) while a TLS connection is being set up. The shared secret allows the bridge to authorize clients after the TLS connection is set up. The shared secret could be sent using AUTHORIZE cells as proposed in #189 and #190. The AUTHORIZE cell could be wrapped in a HTTP GET request header. This should satisfy most goals. - A passive attacker wouldn't be able to distinguish between HTTPS->HTTPS traffic and Tor->Bridge. (Both use TLS) - An active attacker wouldn't be able to fool a client into thinking it was talking to a bridge. (Client would verify identity using fingerprint) - An active attacker wouldn't be able to fool a bridge into thinking it was a client. (No shared secret) To do the actual HTTPS impersonation, we could use Design #3 or #2 from #203. Nginx could be the reverse proxy, forwarding connections to the webserver or bridge as required. Depending on what the bridge is pretending to be, we could simply have nginx sitting in front of the bridge. I'm not sure what type of site the server should pretend to be. Some sort of blog? Maybe a login page? Or it could pretend to be a proxy service or perhaps web based ssh site? Could even be a combination of them I guess. Code changes would include - writing an nginx module to handle authentication - tor would need to handle AUTHORIZE/AUTHORIZED cell Thoughts? Did I miss anything? Thank you for your time, Rohit

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