According to Keybase's documentation:

[The] keybase clients in the wild play a crucial role in keeping the Keybase server honest. They check the integrity of user signature chains, and can find evidence of malicious rollback. They alert Alice when her tracking of Bob breaks, if either Bob or the server was compromised. They check the site's published Merkle tree root for consistency against known signature chains. And they sign proofs when all these checks complete, setting up known safe checkpoints to hold the server accountable to in the future.

And a bit later:

We fully understand that users of the Keybase Web client don't get these guarantees. But our hope is that enough users will use the Keybase command-line client to keep the Web users safe, by catching server misbehavior in the case of a compromise.

If you use the website to sign, verify, decrypt, or encrypt a message, you have to give up your private key and use your passphrase each time. Obviously, that's a risk. But if you sometimes use the website, will using the command line client verify the integrity of the server? Or do I need to trust keybase.io to not get hacked if I ever let it have my private key?

  • What kind of data are you storing on their servers? How confidential is it? – marstato Feb 11 '16 at 23:08
  • @marstato: It's nothing confidential. If it were probably wouldn't use the web interface. I'm just curious. – Ericson Feb 11 '16 at 23:25

The keybase client DOES NOT verify the integrity of the keybase server. The client can to some extent verify behavior of the server to make sure, it is not providing wrong information to clients. That only includes withholding data, for example not saying Alice revoked her key and therefore allowing the compromised key to be exploited. It does not help against the server stealing keys, metadata or any other compromise.

Also, it is important to note, that the server can still pretend to Alice that it is unavailable to prevent her from ever submitting her revocation. While Alice would detect this, no-one else would. Alice would have to inform everyone and somehow prove this, which may be difficult.

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  • This is not (always) true. A server can not only prove to a client the software that it is running (from the kernel to the shell), but also prove that that software is up to date. This is a process called remote attestation. However, I don't believe Keybase does that... – forest Apr 22 '18 at 13:10
  • @forest sorry, I was talking about the keybase client, not in general. That is why as used The. Also, remote attestation is a bit dodgy IMHO. There are many ways it could go wrong. Though better than nothing. – Peter Harmann Apr 22 '18 at 13:16
  • Then I suppose I misunderstood your "can not" (it seems more correct to say "does not", since, in theory, it can). As for remote attestation, it's actually extremely solid. The only thing it relies on is the security of a TPM and its EK. As long as those work, the TCB is reduced to the point that you do not need to trust any other part of the system. – forest Apr 22 '18 at 13:18
  • @forest May want to read about Intel ME, which completely back-doors the whole thing and was found vulnerable in the past. As for the "can not", I meant the server does not provide the necessary data/api. I will edit it though. It makes more sense to say does not. Also, the TPM certificate must be signed by someone, does it not? You must trust both Intel and the CA, which I don't, at least not absolutely. – Peter Harmann Apr 22 '18 at 13:23
  • The CSME can have vulnerabilities the same as any other firmware, but it is far from a backdoor (or at least, it is no more a backdoor than any other parts of the PCH, or the chipset in general). Additionally, it can be disabled in several ways. Remote attestation can allow a server to prove that fact to a client (assuming it switches to a dTPM, because the CSME is what is in charge of the fTPM). – forest Apr 22 '18 at 13:25

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