this post was submitted on 16 Nov 2023
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Proton Mail, the leading privacy-focused email service, is making its first foray into blockchain technology with Key Transparency, which will allow users to verify email addresses. From a report: In an interview with Fortune, CEO and founder Andy Yen made clear that although the new feature uses blockchain, the key technology behind crypto, Key Transparency isn't "some sketchy cryptocurrency" linked to an "exit scam." A student of cryptography, Yen added that the new feature is "blockchain in a very pure form," and it allows the platform to solve the thorny issue of ensuring that every email address actually belongs to the person who's claiming it.

Proton Mail uses end-to-end encryption, a secure form of communication that ensures only the intended recipient can read the information. Senders encrypt an email using their intended recipient's public key -- a long string of letters and numbers -- which the recipient can then decrypt with their own private key. The issue, Yen said, is ensuring that the public key actually belongs to the intended recipient. "Maybe it's the NSA that has created a fake public key linked to you, and I'm somehow tricked into encrypting data with that public key," he told Fortune. In the security space, the tactic is known as a "man-in-the-middle attack," like a postal worker opening your bank statement to get your social security number and then resealing the envelope.

Blockchains are an immutable ledger, meaning any data initially entered onto them can't be altered. Yen realized that putting users' public keys on a blockchain would create a record ensuring those keys actually belonged to them -- and would be cross-referenced whenever other users send emails. "In order for the verification to be trusted, it needs to be public, and it needs to be unchanging," Yen said.

Curious if anyone here would use a feature like this? It sounds neat but I don't think I'm going to be needing a feature like this on a day-to-day basis, though I could see use cases for folks handling sensitive information.

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[–] [email protected] 30 points 2 years ago (3 children)

What is wrong with doing something like pgp key servers?

[–] [email protected] 20 points 2 years ago

Key servers can be dishonest, so you need to have another way of verifying that the key you receive is correct.

[–] [email protected] 11 points 2 years ago (1 children)

Blockchains are an immutable ledger, meaning any data initially entered onto them can't be altered. Yen realized that putting users' public keys on a blockchain would create a record ensuring those keys actually belonged to them -- and would be cross-referenced whenever other users send emails. "In order for the verification to be trusted, it needs to be public, and it needs to be unchanging," Yen said.

[–] [email protected] 8 points 2 years ago (2 children)

How do you ensure the accuracy of the data going into the block chain in the first place?

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[–] [email protected] 3 points 2 years ago* (last edited 2 years ago)
[–] [email protected] 25 points 2 years ago

This is basically like Domain Keys-Identified Mail (DKIM) but for a specific email address, without needing to own a domain to set it up. I'm gonna call it "P(ersonal)KIM" for short.

If this is implemented correctly it'll be a few clicks to set up and then just work in the background to make it harder to impersonate you via email, even if you have a free email address.

[–] [email protected] 21 points 2 years ago* (last edited 2 years ago) (2 children)

It sounds overcomplicated, is there really a need for the blockchain aspect? Could the same security be provided by a simpler method (like how keybase has their identity proofs?) but better to have it and not need it than need it and not have it ig

[–] [email protected] 9 points 2 years ago (18 children)

Right here:

Blockchains are an immutable ledger, meaning any data initially entered onto them can’t be altered. Yen realized that putting users’ public keys on a blockchain would create a record ensuring those keys actually belonged to them – and would be cross-referenced whenever other users send emails. “In order for the verification to be trusted, it needs to be public, and it needs to be unchanging,” Yen said.

The benefit of doing this with a blockchain instead of a privately held and maintained database is that the latter can be compromised, and you just have to trust "whoever" is maintaining that private database. Blockchain means that the ledger is distributed to many nodes, and any post-entry modification to that chain would be instantly recognized, and marked invalid by the other nodes operating the chain. Besides that, when you're looking up a public key for a recipient on such a blockchain, you would be looking it up at a number of nodes large enough that in order for a malicious entry to come through, they would all have to be modified in the same way, at the same time, and you would have to be asking before the change got flagged. Poisoning blockchain data like this is simply not possible; that's what makes this an especially secure option.

[–] [email protected] 7 points 2 years ago (13 children)

But it’s not public. It’s a private blockchain. The immutable ledger aspect only matters if everyone can see the ledger. Otherwise we take at face value all of the things you said. Assume they run one node and that one node is compromised by a malicious actor. The system fails. Extend it to a limited number of nodes all controlled by SREs and assume an SRE is compromised (this kind of spearphishing is very common). The system fails again.

Sure, you can creatively figure out a way to manage the risks I’ve mentioned and others I haven’t thought of. The core issue, that it’s not public, still remains. If I’m supposed to trust Proton telling me the person I’m emailing is not the NSA pretending to be that person (as the Proton CEO suggested), I need to trust their verification system.

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[–] [email protected] 17 points 2 years ago* (last edited 2 years ago)

I would strongly assume Protonmail will be doing this automatically soon, there's no manual day-to-day verification necessary.

Writing to the Blockchain is difficult and takes processing power, reading from it is absolutely trivial though.

[–] [email protected] 11 points 2 years ago (1 children)

I’ll use it once they’ve sorted out CalDAV and CardDAV… it’s only been an open issue for eight fucking years.

[–] [email protected] 4 points 2 years ago (1 children)
[–] [email protected] 4 points 2 years ago

There’s no way to sync contacts and calendars between an iPhone (and other mail clients) and protonmail. The app does one way sync from the phone to protonmail, but not the other way round.

8 years ago a feature request was made to add support for CardDAV and CalDAV, but even with the release of bridge it’s not there.

So iOS users have to resort to using other calendar services, or 3rd party bridges to enable it.

[–] [email protected] 7 points 2 years ago* (last edited 2 years ago) (1 children)
[–] [email protected] 21 points 2 years ago (5 children)

This is false. Protonmail has supported Web Key Discovery for external domains since 2019: https://proton.me/blog/security-updates-2019

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