4 ms·

> like Wire but without the video calling or end to end encryption I'm not quite sure what you mean here, but Keybase does have end to end encryption—I think t

by Gaelan 7y ago

> like Wire but without the video calling or end to end encryption I'm not quite sure what you mean here, but Keybase does have end to end encryption—I think they're trying to position themselves as "Slack with end-to-end encryption."

lucb1e 7y ago
The app is only end to end encrypted if you trust the server to give you the right keys from the beginning (it's E2EE meets TOFU): since there is no way to verify what information (the "sigchains") the server sent to your device (no safety number like in signal, encryption key like in Telegram, fingerprint like in Wire, or whatever you call it), you have to trust the server. The app does verify that nothing changes, so the server has to consistently lie to the device, and to app clients only because a command line client could verify the keys. Then again, since very, very few people do or can do this verification, and since the verification tutorial in the documentation is relatively complex and broken (an api call doesn't return a signatures field the tutorial relies on) and nobody seems to have noticed, it's probably a safe bet for an attacker that compromised the server to just MITM all devices of some users without being noticed. Note that the blockchain magic does nothing because the app doesn't verify it, and if it did, it would have to be a normal bitcoin client, which would take lots of traffic, storage (even with SPV, you need all the block headers), and shifts the trust to a lot of third parties instead of one (so that's quite trustworthy and great for my grandma that doesn't verify keys, but personally I'd prefer to just check a key in favor of running a bitcoin client on my phone). But that's not implemented yet so this point is moot anyway. And if I'm not mistaken, one needs to compute the merkle tree completely, that is, hash all sigchain of all Keybase users (imagine they become popular and you have to download a literal billion sigchains and hash them all together on a phone) to match it against the final value you get from the blockchain. Finally, someone brought up verifying keys with another device. I'm not sure if that works. It might, depending on how the key exchange works and if it forces you to verify something in the app. If you don't, I mean, in the situation that the server spoofs your sigchain (MITM) to your friends, it can do that between your devices as well and report whatever value it used for the merkle tree to your command line client so everything checks out. So it's not completely broken, but trusting the server on first use is m a lesser guarantee than all other E2EE software, and the fix is really simple so I don't get why they don't implement it (note that I don't mean to hint that they're indeed MITMing and that's why they don't let people verify it; I genuinely don't understand why not allow people to do this, I see no reason). My best guess is that they either didn't think of the scenario themselves (and NCC also missed it, which makes sense since they verified the crypto and code and not how a normal user would actually verify this in the UI) or they don't want to admit now that it depended on closed source servers being trusted all along. Relevant question: https://security.stackexchange.com/questions/222055/how-can-i-verify-keybases-end-to-end-encryption-between-me-and-a-friend https://security.stackexchange.com/questions/222055/how-can-...
- ahnick 7y ago
  Sorry, but doesn't the client check the published keys itself? According to this document the client verifies the key that has been published on twitter or wherever else the user you are interacting with has publicly confirmed his/her identity. https://keybase.io/docs/server_security/following https://keybase.io/docs/server_security/following My understanding is in the event of a server compromise in the beginning then the fake public key for the user that the malicious server would be sending would be easily detectable due to this client side check that is occurring. Whoever is behind the MITM attack would also have to compromise Twitter and all other places the user you are chatting with has published, no?
  - lucb1e 7y ago
    I didn't connect my account to Twitter or HN or anything, I just have a Keybase account to chat with a friend and wanted to check whether it's secure. I guess this could work though, from the app I can indeed configure third party accounts (I guess in some next step, it'll tell me what to tweet to prove it). Assuming my phone generates the proof locally, that would prove it without doing manual verification, unless both Keybase and Twitter collude to attack us (or an attacker compromised both or sent NSLs to both), so that seems extremely unlikely. Does the Keybase client check this by itself though? It seems a bit odd, the app connecting to third parties, but it could be. Like, I'd find out your IP address by adding a website proof where I host a text file. We can test this if you want? Then I'll pcap my phone and see, while adding you, if my client connects to whatever third party you have configured.
    - ahnick 7y ago
      Yes, supposedly the client scrapes it using the website. They have a number of third party integrations they do this for. It's actually a point of contention for them to add more third parties within the community. (People wanted LinkedIn and various other services) Going forward they want it to be the other way around and have third parties to start integrating with Keybase. (https://keybase.io/docs/proof_integration_guide https://keybase.io/docs/proof_integration_guide) Yeah, feel free to message me to test it out. My proof on twitter is here -> https://twitter.com/xan_nick/status/860495425920524290 https://twitter.com/xan_nick/status/860495425920524290. You should also see it verify my HN and github, which I also have connected. (https://keybase.io/ahnick https://keybase.io/ahnick) Definitely interested in your results.

by Gaelan 7y ago

lucb1e 7y ago

The app is only end to end encrypted if you trust the server to give you the right keys from the beginning (it's E2EE meets TOFU): since there is no way to verify what information (the "sigchains") the server sent to your device (no safety number like in signal, encryption key like in Telegram, fingerprint like in Wire, or whatever you call it), you have to trust the server. The app does verify that nothing changes, so the server has to consistently lie to the device, and to app clients only because a command line client could verify the keys. Then again, since very, very few people do or can do this verification, and since the verification tutorial in the documentation is relatively complex and broken (an api call doesn't return a signatures field the tutorial relies on) and nobody seems to have noticed, it's probably a safe bet for an attacker that compromised the server to just MITM all devices of some users without being noticed. Note that the blockchain magic does nothing because the app doesn't verify it, and if it did, it would have to be a normal bitcoin client, which would take lots of traffic, storage (even with SPV, you need all the block headers), and shifts the trust to a lot of third parties instead of one (so that's quite trustworthy and great for my grandma that doesn't verify keys, but personally I'd prefer to just check a key in favor of running a bitcoin client on my phone). But that's not implemented yet so this point is moot anyway. And if I'm not mistaken, one needs to compute the merkle tree completely, that is, hash all sigchain of all Keybase users (imagine they become popular and you have to download a literal billion sigchains and hash them all together on a phone) to match it against the final value you get from the blockchain. Finally, someone brought up verifying keys with another device. I'm not sure if that works. It might, depending on how the key exchange works and if it forces you to verify something in the app. If you don't, I mean, in the situation that the server spoofs your sigchain (MITM) to your friends, it can do that between your devices as well and report whatever value it used for the merkle tree to your command line client so everything checks out. So it's not completely broken, but trusting the server on first use is m a lesser guarantee than all other E2EE software, and the fix is really simple so I don't get why they don't implement it (note that I don't mean to hint that they're indeed MITMing and that's why they don't let people verify it; I genuinely don't understand why not allow people to do this, I see no reason). My best guess is that they either didn't think of the scenario themselves (and NCC also missed it, which makes sense since they verified the crypto and code and not how a normal user would actually verify this in the UI) or they don't want to admit now that it depended on closed source servers being trusted all along. Relevant question: https://security.stackexchange.com/questions/222055/how-can-i-verify-keybases-end-to-end-encryption-between-me-and-a-friend https://security.stackexchange.com/questions/222055/how-can-...

ahnick 7y ago
Sorry, but doesn't the client check the published keys itself? According to this document the client verifies the key that has been published on twitter or wherever else the user you are interacting with has publicly confirmed his/her identity. https://keybase.io/docs/server_security/following https://keybase.io/docs/server_security/following My understanding is in the event of a server compromise in the beginning then the fake public key for the user that the malicious server would be sending would be easily detectable due to this client side check that is occurring. Whoever is behind the MITM attack would also have to compromise Twitter and all other places the user you are chatting with has published, no?
- lucb1e 7y ago
  I didn't connect my account to Twitter or HN or anything, I just have a Keybase account to chat with a friend and wanted to check whether it's secure. I guess this could work though, from the app I can indeed configure third party accounts (I guess in some next step, it'll tell me what to tweet to prove it). Assuming my phone generates the proof locally, that would prove it without doing manual verification, unless both Keybase and Twitter collude to attack us (or an attacker compromised both or sent NSLs to both), so that seems extremely unlikely. Does the Keybase client check this by itself though? It seems a bit odd, the app connecting to third parties, but it could be. Like, I'd find out your IP address by adding a website proof where I host a text file. We can test this if you want? Then I'll pcap my phone and see, while adding you, if my client connects to whatever third party you have configured.
  - ahnick 7y ago
    Yes, supposedly the client scrapes it using the website. They have a number of third party integrations they do this for. It's actually a point of contention for them to add more third parties within the community. (People wanted LinkedIn and various other services) Going forward they want it to be the other way around and have third parties to start integrating with Keybase. (https://keybase.io/docs/proof_integration_guide https://keybase.io/docs/proof_integration_guide) Yeah, feel free to message me to test it out. My proof on twitter is here -> https://twitter.com/xan_nick/status/860495425920524290 https://twitter.com/xan_nick/status/860495425920524290. You should also see it verify my HN and github, which I also have connected. (https://keybase.io/ahnick https://keybase.io/ahnick) Definitely interested in your results.