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Comment by 0xDEAFBEAD | Hacker News Reader

I think you'd need to do it out of band though, otherwise you're vulnerable to MITM? (That's the primary attack this is meant to protect against, I think?)

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Depends on your threat analysis. If you're not considering an active attacker who has an ability to seamlessly fake voice and/or face to be a realistic attack scenario (e.g. you're guarding against mass surveillance, but not a prepared targeted attack - i.e. you don't find it plausible that someone has prepared actors - human or machine - with quality deepfakes made specially for you and your peer) and you know the other party personally, you can verify in-band, relying on natural biometrics aka your knowledge of one's voice and face. If you do - certainly the verification must be done out-of-band.

I can't imagine what it would be like to actually have to deal with the scenario you described.

Customized deepfake attacks are definitely happening:

https://www.npr.org/2023/03/22/1165448073/voice-clones-ai-sc...

https://www.forbes.com/sites/thomasbrewster/2021/10/14/huge-...

My thinking is, you might as well get in the habit of defending yourself now. The alternative is to monitor how widespread the attack is and only adjust your policy once it becomes "sufficiently" widespread. But I don't think that's even a labor savings, since defending yourself isn't actually that hard.

The man in the middle would need to spoof the voice (with current microphone+environment etc.) in ~real time, probably both parties as well. And with the awareness to detect which words to replace in the middle of a normal conversation.

With the demos we've seen feels absolutely doable, but for now requires quite some effort.

You're talking about an attacker who wants to tamper with communication. Eavesdropping is far easier. [I agree you'll want deepfakes if you want your MITM eavesdropping to handle emoji codes, for mass surveillance at least.]

But even tampering seems pretty easy if the attacker has a more modest objective, of having you and your buddy each talking to one of the attacker's henchmen using voice changers. The emoji verification won't help here -- each henchman just gives the emoji for their respective conversation.

Yes the whole point was how you'd have to deal with the emojis.

I feel it is implied that the latency is low enough (a few 100s of ms) to not impede the conversation, and that the parties have talked before and would notice if the tone of the conversation was completely different. Or maybe I'm misunderstanding.

Yeah that seems right. I guess an attacker could tamper with the call early on, say "hey what are your emojis?" as soon as the call starts. Deepfaked voices and 2 henchmen should be sufficient here, no need for real-time audio rewriting. Then once the emojis have been verified, switch to a pure-eavesdrop MITM.

To defend, could ask to verify emojis at a random point in the middle of the call to make the attacker's life more difficult. Especially right before discussing sensitive information ;-)

Or drip verify over the course of the call, e.g. "what's your 3rd emoji?", and listen for signs of an attacker cutting in and out.

This is when multifactor includes "what you know they know about you" and specialized in-group slang is the real mark of credit.

That doesn't help in a hypothetical where the attacker is doing a passive audio-forwarding ("pure eavesdrop") MITM for everything except emoji verification.

There are four emojis. I reveal the first 1, they reveal the 2 nd, etc. how many rounds of exchange do you need to happen to be safe?

If the process you just described was actually secure then the computers could verify on its own. The problem is with an active mitm attack the attacker knows both sets of emojis and can modify the messages to both parties to look like they recieved the correct ones.

if this is voice chat, in-band might be good enough. There is no technology (yet?) which can real-time recognize spoken emoji description like "weird cucumber with mouth.. wait I think its an alligator or maybe even a crocodile?" and then retroactively replace it with a different one while keeping the timing correct.

OLVID App by the French Government asks users to swap a 4 digit PIN. App is great for OpSec check it out.

> OLVID App by the French Government

Recently the French Government required its members to use it, but it's made by a French startup, AFAIK.

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