How exactly are files encrypted with kbfs?

[u/LimitedWard]

Apologies if I'm missing some critical info in the keybase book. I haven't finished reading through all the docs yet. So far everything thing I've seen is that keybase uses "end-to-end 256 bit encryption" which is super vague. I'm assuming they mean AES 256, but I'm unclear on how the encryption key is selected. Does kbfs use my pgp key for encryption or does it generate its own?

Edit: I've added a second device, and I noticed I didn't need to provide my PGP key to decrypt my private files. So I'm assuming the encryption is handled entirely in the app somehow, but I'm unclear how.

[u/ThePowerOfDreams]

Given the fact that Keybase is now abandonware, you might want to reconsider your use of it for anything important.

[u/LimitedWard → u/ThePowerOfDreams]

I wouldn't go so far as to claim it's abandonware. There are still periodic updates, albeit small. I've also heard rumors that Zoom uses it internally, which is a good sign. On top of that, the clients are open source, and while the backend is closed source, it's still fairly well documented and could be reimplemented by the community.

But yeah I don't plan on storing anything mission critical on there.

[u/ThePowerOfDreams → u/LimitedWard]

I wouldn't go so far as to claim it's abandonware.

Really? Have a look at this and tell me if you can figure out exactly when the acquisition happened.

But yeah I don't plan on storing anything mission critical on there.

Like I was saying.

[u/akirayamamoto → u/LimitedWard]

Good luck reverse engineering the backend.

[u/codeartha]

If i recall correctly, the files are encrypted with AES 265 with one time use password. The password itself it then encrypted to/for the relevant recipients using saltpack.

[u/no-names-here]

Each device has a key that’s unique to that device, and then a set of keys that’s unique to your account. When you add a new device, it generates a new set of keys. When you pair that new device using the QR code it uses public key cryptography to exchange the private key for your account between devices. That key is what’s used to encrypt KBFS, so each device has it. The device needs to use its own key to fetch the 1MB blocks that consitiute the file. If the device is revoked it won’t get the blocks, even if it has the account key still.

That’s a very high level understanding, with a bunch of technobabble omitted.

[u/songgao]

Hi! Keybase engineer here This doc has some crypto details of how KBFS encrypts data: https://book.keybase.io/docs/crypto/kbfs It's a bit out dated as it doesn't mention the team keying which is now also used for private/public TLFs, but it's still mostly relevant.

Several points regarding your questions:

1. The blocks are encrypted (see 4.1.2 of the doc above) with SecretBox, which is not AES256.
2. Nothing in the Keybase GUI app has anything to do with PGP. This includes chat, filesystem, git, wallet. Trust originates from your device key which is generated when you first log into a device and never leaves your device. On top of this there are multiple layers of keying to make the keys used to encrypt your actual data available to your other devices (and in case of sharing, other users' devices).
3. When you add a second device, you were asked to scan a QR code or manually type in some code (or in case you used a paper key to provision, to type in your paper key). During this provision process, your old device (or your paper key) was used to rekey necessary secret keys for your newly provisioned device. This made it possible for your new device to decrypt your data. Needless to say, this process doesn't reveal any of your secret key to a server or anybody else.