Jeffrey Paul: Keybase iOS Has A Backdoor

Jeffrey Paul

Keybase iOS Has A Backdoor
29 September 2019
( 545 words, approximately a 3 minute read. )

Keybase’s iOS client has received a backdoor.

It seems that Stellar, the extremely well-funded and well-marketed cryptocurrency, has struck a deal with Keybase to “airdrop” (give away) their tokens to keybase users in an effort to drive adoption.

Keybase updated their iOS client to sign an attestation, as a user, that a given stellar address belongs to them, even if it does not. This is done without any user interaction or consent, violating the fundamental principle of Keybase’s product until now: the user controls their keys.

Of course, the user controls their keys using Keybase’s software, which, under normal circumstances, means the user controls their keys. But in this instance, Keybase’s software decided to sign, for a user, without their knowledge or consent, an attestation saying that username*keybase.io is a legitimate stellar payment address for the user—even if the user has never heard of it.

Here’s mine. Note: DO NOT send payments to this address! I don’t have the keys for this address, don’t control this address, and don’t want any XLM shitcoins even if I did–despite what Keybase’s client has claimed with my private keys.

There is no option to remove this payment address from my Keybase profile, turning my Keybase profile page into an ad for a shitcoin, using my name, face, and identity as an implicit endorsement for Stellar. This is rude and unethical.

Keybase, I understand that you have no good revenue model. I know that good software costs money. I don’t have an alternative for you, but if selling out your users and violating their trust and consent (and, by extension, fraudulently claiming that published cryptocurrency addresses represent payment addresses for your users) is the best you can think of, then perhaps you should give up and stop existing as a concern.

I have filed this as a bug, although I doubt it will be addressed sufficiently, as this is intentional behavior on the part of Keybase, who have hopefully been well-paid by Stellar for entirely undermining their tool’s trust.

Edit/Update

There seems to be some semantic bickering around whether or not an encryption tool silently making signatures in violation of a user’s wishes (and in service of the financial aims of the maker of that tool) qualifies as a “backdoor”.

Keybase themselves have used the term ‘backdoor’ to refer to an encryption program signing additional, unwanted keys against a user’s wishes.

This is a common, accepted usage in cryptography circles: when a tool that is used for signing or encryption/decryption creates a signature or decrypts a message for anyone other than the user, especially without the knowledge or consent of that user, it has hijacked use of the user’s keys and is no longer serving that user, but a remote attacker. That’s a backdoor.

Edit 2

Don’t worry, everyone. The guy who got paid a bunch of money to force these ads onto your profile said it’s not a backdoor. He used all caps, so you know he means it. The capital-followers at HN have killed the link to this page, because the perpetrator said there’s nothing to see here. The dozens of other users experiencing similar problems must be mistaken, too, about what they wanted their keys to do.

About The Author

Jeffrey Paul is a hacker and security researcher living in Berlin and the founder of EEQJ, a consulting and research organization.

@sneakdotberlin

@eeqj

sneak@sneak.berlin

keybase.io/sneak

linkedin.com/in/jeffreypauleeqj