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.
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.
‘Man in the middle’
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.
Threat model
The feature will be automatic for users of Proton, which will do a search to ensure that the public key matches the intended recipient. If there isn’t a match, users will see a warning.
Proton rolled out the beta version of Key Transparency on their own private blockchain, meaning it’s not run by a decentralized series of validators, as with Bitcoin or Ethereum. Yen said Proton might move the feature to a public blockchain after the current version serves as a proof of concept.
In his interview with Fortune, Yen acknowledged that the feature isn’t necessarily for everyday people, but for users with a sophisticated threat model who need to ensure their emails are going to the correct destination, such as world leaders, executives, and activists.
Despite the niche use case, he said Proton Mail currently has 100 million accounts and is starting to gain more mainstream interest amid privacy concerns around leading email clients like Gmail, which tracks user behavior.
“It’s really a way to opt out of the mass surveillance that today is the prevalent model on the internet,” he said. “That’s why the average user should decide to switch.”
