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Technology preview: Private contact discovery for Signal

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Re: Technology preview: Private contact discovery for Signal

#61

Post by DINKDINK »

hardwarescope wrote: post #11
DINKDINK wrote: post #5

The security assumptions that SGX is built on are flawed. They assume that no side channel attacks will be mounted to determine the processes that occur in side the chip. You can even build software to do side channel analysis on the physical chip: 7:16:26 Daniel Gruss / Michael Schwarz - Cache Attacks on SGX https://youtu.be/eCE2OzKIab8?t=26193

> They assume that no side channel attacks will be mounted to determine the processes that occur in side the chip. They do? 2/3rds of this blog post are about side channel attacks. The majority of the technical aspects of the article are about memory side channels in SGX and how they overcome those challenges. I haven't looked at the code yet, but it sounds as if they wrote it to be branchless so that attackers can't…

You're correct. My original statement was wrong regarding Intel's assumption. The principle issue is that developers shouldn't assume that processes that occur in SGX are obfuscated in any sense because you can build SGX sidechannel detection within software that runs inside the enclave The lecture I pointed to shows an example of this attack.

Re: Technology preview: Private contact discovery for Signal

#62

Post by jlgaddis »

thinkloop wrote: post #54

> The obvious problem with this method is that the hash of a user identifier can almost always be inverted. Regardless of whether the identifier is a phone number, a user name, or an email address, the “keyspace” of all possible identifiers is too small. What does "inverted" mean here? And why is the keyspace too small? And how do these problems relate to not trusting the server? The problem definition and proposed s…

Imagine you're storing a four-digit PIN (or even 10-digit phone numbers in the U.S.) and you decide to hash them with SHA256 because security.

The key space -- the total number of all possible PINs -- is really small; there are only 10,000 of them. One could simply "pre-compute" the SHA256 hashes of all 10,000 possible PINs and store them in a table.

When you receive a hashed value, it's really simple -- and, more importantly, very fast -- to just look up the hash in the table and get back the original PIN (a.k.a. "inverting" it).

It's kinda the same thing as "rainbow tables", if you recall those.

Re: Technology preview: Private contact discovery for Signal

#63

Post by tveita »

bascule wrote: post #51
zeveb wrote: post #50

Earlier quoted context omitted.

The two users are two folks who wish to communicate who hold their phones back-to-back and let NFC validate who they each are. Both parties are now able to perform a private set intersection to find people whom they know in common who also use Signal, and are able to then use private set intersection with each of those people to find more. The idea is that users bootstrap via the social graph of folks they physically…

So you want to completely punt on the "open the app to an empty contact list" problem and force people to perform what's effectively a GPG keysigning party... Call me crazy, but I think that'd be a bad user experience of the sort that held back encrypted messaging for decades.

They could at least allow it. Signal is the odd one out among secure messenger apps for having no way of adding a contact in a face to face setting without uploading all your contacts to their servers.

Re: Technology preview: Private contact discovery for Signal

#64

Post by davidad_ »

rdl wrote: post #46

This is definitely interesting (and probably the first end-user-valuable SGX-on-server application I've seen), but there are two issues IMO: 1) Intel SGX isn't really capable of resisting moderately serious physical side channel attacks by someone with physical proximity or access to the server. It's decent for low-value, or widely deployed apps where compromise of a single instance only hurts once user, but for a ce…

From what I can tell, it's worse than just Intel being a gatekeeper - every execution of "remote attestation" essentially relies upon the Intel Attestation Service to actually perform verification (or at least as the certificate authority). In a (hypothetical) world where all of Intel's security features are owned by the US intelligence community, this type of pattern seems like an awesome vector for deception ("false sense of security"), where surveillance groups have a large supply of Intel-certified EPID keys, which they can use to arbitrarily fool remote-attestation clients. It's concerning to me that the OP article doesn't even mention Intel's highly trusted role in this process.

Re: Technology preview: Private contact discovery for Signal

#65

Post by mintplant »

dublinben wrote: post #55
mintplant wrote: post #36

In case someone from Open WhisperSystems is reading: please add stickers. Seriously, I know so many people who are on Telegram just because of its sticker system and won't consider anything without that feature. This comes up again and again in online discussions where Signal is mentioned, and it hurts to see all the care and effort the OWS team has put into providing real security rejected out of hand because of it.…

You can already send arbitrary images and attachments in Signal messages.

Sure, but compared to the stickers UI paradigm it's far clunkier to browse for an image file every time and to collect and arrange image files sent by other people, particularly on a mobile device.

Also, stickers display with proper transparency, giving them the appearance of arbitrary shapes, whereas images on Signal are displayed in a rectangular frame and transparent areas get a black background.

Compare:

https://image.ibb.co/niKWUQ/IMG_20170926_135611.jpg

with:

https://preview.ibb.co/fg21UQ/IMG_20170926_135627.jpg

It may seem trivial, but this matters to people in the real world.

Re: Technology preview: Private contact discovery for Signal

#66

Post by ycmbntrthrwaway »

thinkloop wrote: post #52
mintplant wrote: post #36

In case someone from Open WhisperSystems is reading: please add stickers. Seriously, I know so many people who are on Telegram just because of its sticker system and won't consider anything without that feature. This comes up again and again in online discussions where Signal is mentioned, and it hurts to see all the care and effort the OWS team has put into providing real security rejected out of hand because of it.…

In case someone from Open WhisperSystems is reading: please do NOT add stickers and junk to your clean and pretty system. I know a lot of people that would leave the service if it turned into WeChat (including me). Stick to the fundamental engineering of privacy as you are doing, and forget the gimmicks.

> I know a lot of people that would leave the service if it turned into WeChat (including me).

Where will they go? To some less secure alternative simply because of stickers?

Re: Technology preview: Private contact discovery for Signal

#67

Post by ycmbntrthrwaway »

dublinben wrote: post #55
mintplant wrote: post #36

In case someone from Open WhisperSystems is reading: please add stickers. Seriously, I know so many people who are on Telegram just because of its sticker system and won't consider anything without that feature. This comes up again and again in online discussions where Signal is mentioned, and it hurts to see all the care and effort the OWS team has put into providing real security rejected out of hand because of it.…

You can already send arbitrary images and attachments in Signal messages.

Using this feature instead of stickers is like using imageboard on your phone.

Re: Technology preview: Private contact discovery for Signal

#68

Post by orbifold »

thinkloop wrote: post #52
mintplant wrote: post #36

In case someone from Open WhisperSystems is reading: please add stickers. Seriously, I know so many people who are on Telegram just because of its sticker system and won't consider anything without that feature. This comes up again and again in online discussions where Signal is mentioned, and it hurts to see all the care and effort the OWS team has put into providing real security rejected out of hand because of it.…

In case someone from Open WhisperSystems is reading: please do NOT add stickers and junk to your clean and pretty system. I know a lot of people that would leave the service if it turned into WeChat (including me). Stick to the fundamental engineering of privacy as you are doing, and forget the gimmicks.

In my opinion the signal ios client is significantly less polished than the telegram client. I could convince my girlfriend to switch to telegram, after she found signal to be intolerable on her android device as well.

Re: Technology preview: Private contact discovery for Signal

#69

Post by bascule »

tveita wrote: post #63
bascule wrote: post #51

Earlier quoted context omitted.

So you want to completely punt on the "open the app to an empty contact list" problem and force people to perform what's effectively a GPG keysigning party... Call me crazy, but I think that'd be a bad user experience of the sort that held back encrypted messaging for decades.

They could at least allow it. Signal is the odd one out among secure messenger apps for having no way of adding a contact in a face to face setting without uploading all your contacts to their servers.

Signal allows you to send messages to numbers which are not in your contacts, which by definition implies it can be done without uploading your contacts to your servers.

In person you can also exchange "safety numbers" via QR code which provides key verification.

Re: Technology preview: Private contact discovery for Signal

#70

Post by thinkloop »

mintplant wrote: post #59
thinkloop wrote: post #52

Earlier quoted context omitted.

In case someone from Open WhisperSystems is reading: please do NOT add stickers and junk to your clean and pretty system. I know a lot of people that would leave the service if it turned into WeChat (including me). Stick to the fundamental engineering of privacy as you are doing, and forget the gimmicks.

I don't understand your motivation here. Every time I advocate using Signal I run into a wall of "but it doesn't have stickers"; for those users, all the privacy engineering is moot if the app doesn't fill their needs. Adding another attachment type would do nothing to degrade your experience, nor would it turn Signal into WeChat.

It does degrade it tho. There have to be ui elements to interact with them, you need to be up to date on packs, a market needs to be implemented, maybe payment needs to be introduced, the chat looks ugly full of graphics, etc. Plus, every feature adds vectors of attack and things to maintain. I want this to be a Snowden'ish tool for adults, not giffy. I'm not saying my preferences are any better than yours, just highlighting that there are varied preferences out there. If signal started looking like WeChat or Messenger I'd probably leave.
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