Researchers find critical flaws in the tech underpinning email encryption

Researchers find critical flaws in the tech underpinning email encryption

Security researchers detail a series of flaws in the widely deployed OpenPGP and S/MIME standards that could potentially enable an attacker to decrypt emails.

Some security experts said that because EFAIL seems to affect specific email applications, it is overkill to say that there is a flaw in the actual underlying encryption protocols.

Some people are saying this is an overreaction, but if you would like to be certain, the EFF has released guides on how to disable PGP encryption in Apple Mail, Outlook, and Thunderbird. The attack works for emails even if they were collected long ago, and is triggered as soon as the recipient decrypts a single maliciously crafted email from the attacker.

"There are now no reliable fixes for the vulnerability", Schinzel says via Twitter. More details are starting to drip out, but the warning is that leaving encryption active will increase the danger and so for now, using something safe is the best course of action.

Of course, if you recognise the need to secure encrypt your communications you probably also understand that resorting to sending and receiving unencrypted email is far from an acceptable solution. The Foundation which has been in communication with the researchers has advised users to "temporarily stop sending and especially reading PGP-encrypted email". "This vulnerability might be used to decrypt the contents of encrypted emails sent in the past".

More details are to be published on May 15 at 07:00 AM UTC (3:00 AM Eastern, midnight Pacific) by the team. The Electronic Frontier Foundation, a separate technology advocacy group that previewed the researchers' findings on Sunday, said users of the affected email programs should disable any third-party software they have installed that allow the email apps to use PGP or S/MIME. In one attack method, the researchers take advantage of Cipher Feedback Mode (CFB) in OpenPGP and Cipher Block Chaining (CBC) in S/MIME.

"In the most straightforward example of our attacks, the adversary prepares a plaintext email structure that contains an img element, whose URL is not closed with quotes", the researchers wrote. These tools are commonly employed by journalists, politicians, and other users who require secure communication. They might reveal the plaintext of encrypted emails, including encrypted emails sent in the past.

They then would have to send the contents of that encrypted email back to its owner - the victim - in a carefully crafted way to make email clients think it's HTML.

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