[HN Gopher] Private contact discovery for Signal (2017)
___________________________________________________________________
Private contact discovery for Signal (2017)
Author : tchalla
Score : 28 points
Date : 2021-02-27 19:23 UTC (3 hours ago)
(HTM) web link (signal.org)
(TXT) w3m dump (signal.org)
| A_Duck wrote:
| Some low-tech alternatives
|
| (1) Each client app to submit x randomly generated phone numbers
| for every real number, making any reconstructed social graph
| useless and deniable. Where x is the slowdown their very cleverly
| over-engineered solution introduces...
|
| (2) As long as Signal user base is relatively small -- submit n-1
| digits of the number, then wait for confirmation there is at
| least one Signal user matching before submitting the final digit.
|
| (3) If user base is larger - submit n-1 digits of the phone
| number, and receive all of the up to 10 matching users
| Closi wrote:
| I assume you can still build a social graph with number 1 with
| enough people using the service if you just check for 2 way
| connections between contacts (i.e. if Jane submits a contact
| list including Simon, Pete and Paul, and Paul submits a contact
| list including Sarah, Francis and Jane, I can imply that Jane &
| Paul are real contacts).
|
| 2 & 3 seem to match the 'bloom filter' concept described here:
| https://signal.org/blog/contact-discovery/
| mikece wrote:
| "Signal is social software. We don't believe that privacy is
| about austerity, or that a culture of sharing and communication
| should mean that privacy is a thing of the past."
|
| I don't agree. All I want from Signal is an e2ee, cross-platform
| replacement for SMS. I don't think of SMS as "social software"
| and to the degree Signal keeps acting like it wants to be a
| social network the more uneasy it makes me. I do appreciate that,
| unlike Telegram, I can use Signal without giving it access to my
| contacts but I wish it didn't try to leverage my contacts list at
| all.
| swiley wrote:
| Just use email with autocrypt or jabber with OMEMO. Signal will
| always have its way because it isn't federated.
| Sunspark wrote:
| Signal is not a social network, and it's the cross-platform
| replacement for SMS that you want it to be. Essentially RCS in
| that it requires a data network, but is better designed.
|
| I don't think it's an issue that it uses your contact list. Why
| should that be a concern? It doesn't upload them into a
| database like other services.
|
| Signal is a privacy app, not an anonymity app.
|
| I see people expressing their concern about seeing their boss
| using the app, etc. and I just cannot relate. Is their argument
| that they prefer to use insecure SMS with their boss instead?
| What's the point? Both parties _already have_ each other's
| phone number as a unique identifier.
|
| I only have a limited # of people I can use Signal with because
| I don't post my phone number everywhere, though I am old enough
| that I remember telephone books back when people used to give
| out their phone number and address and nobody thought anything
| of it.
| electriclove wrote:
| Why is it a concern that an app wants to use my contact list?
| Really??
| Sunspark wrote:
| Given that it isn't uploaded into a database, it shouldn't
| be a concern for you, and if it is, you better stop using
| your smartphone because you're already sharing it with
| Google.
| electriclove wrote:
| I use Signal and don't like that it wants access to my
| contact list. I want a better way and if my little voice
| adds to a call for a better way, great. Don't tell me I
| shouldn't care.
| Sunspark wrote:
| You got the better way already. It's not being uploaded
| into a database.
| lrvick wrote:
| Beyond the KYC requirements in 200 countries that make phone
| number based systems useless for those in high risk
| situations... They have other less obvious problems.
|
| Today with a phone number you can:
|
| 1. Port it, steal 2FA and password resets, take over critical
| accounts that don't allow alternate 2FA (happened to two
| friends of mine that work on financial security)
|
| 2. Pay first party or shady second party bounty hunter cell
| carrier APIs to get current GPS location on a number.
|
| I do not even have a cell carrier anymore for these reasons,
| social consequences be damned.
| user-the-name wrote:
| I am pretty sure that SMS leverages your contact list, though.
| If you want Signal to replace it, then, why should it not do
| the same?
| captainmuon wrote:
| How does this ensure that the code on the server is running on
| the secure enclave, and not in an emulation[2]? Or that the whole
| attestation is not emulated? How do we know that the team who
| built the SGX does not work closely with the NSA[1]?
|
| I would probably just concatenate the phone numbers with the
| user's numbers, throw in some hard to guess salt like the Dow
| Jones index, and hash it with bcrypt. It's not perfect, but I
| would consider it good enough. And most importantly, easier for
| me to verify.
|
| ([1] Only half kidding: My favorite paranoid theory is that most
| security tech is thoroughly backdoored, and most of the
| 30000-40000 employees of NSA are actually doing parallel
| contruction all day long for the data they get this way.)
|
| [2] Edit: from skimming the previous HN discussion, it seems that
| SGX relies upon Intel's remote attestation service. The code you
| run is signed by Intel, and you have a chain of trust stemming
| from a key held by Intel. It's a clever construction, but I still
| feel it is too clever to be comfortable with.
| lrvick wrote:
| But the signing key could of been extracted via a number of
| side channel attacks on SGX.
|
| SGX remote attestation is, given those exploits, a super weak
| assurance of anything.
|
| Centralization of security and privacy is universally a
| mistake.
| devadvance wrote:
| Previously discussed here:
| https://news.ycombinator.com/item?id=15340729
|
| As an engineer, I appreciate the depth of this post. However, I'd
| also appreciate a more approachable version that I could share
| with a broader audience. E.g., without understanding anything
| about hashing, SGX, etc., how can we best explain the advantages
| of this approach over the "upload your contacts list" request
| that you encounter in other chat apps?
___________________________________________________________________
(page generated 2021-02-27 23:00 UTC)