alt Hacker NewsI wasn’t aware of the efail disclosure timeline. Apparently Koch responds to the report by noting that GPG prints an error when MDC is stripped, which has eerie parallels to the justification behind the recent gpg.fail WONTFIX response (see https://news.ycombinator.com/item?id=46403200)
I think the two cases are different. The EFAIL researchers were suggesting that the PGP code (whatever implementation) should throw an error on an MDC integrity error and then stop. The idea was that this would be a fix for EFAIL in that the modified message would not be passed on to the rest of the system and thus was failsafe. The rest of the system could not pass the modified message along to the HTML interpreter.
In the gpg.fail case the researchers suggested that GPG should, instead of returning the actual message structure error (a compression error in their case), return an MDC integrity error instead. I am not entirely clear why they thought this would help. I am also not sure if they intended all message structure errors to be remapped in this way or just the single error. A message structure error means that all bets are off so they are in a sense more serious than a MDC integrity error. So the suggestion here seems to be to downgrade the seriousness of the error. Again, not sure how that would help.
In both cases the researchers entirely ignored regular PGP authentication. You know, the thing that specifically is intended to address these sorts of things. The MDC was added as an afterthought to support anonymous messages. I have come to suspect that people are actually thinking of things in terms of how more popular systems like TLS work. So I recently wrote an article based on that idea:
* https://articles.59.ca/doku.php?id=pgpfan:pgpauth
It's occurred to me that it is possible that the GnuPG people are being unfairly criticized because of their greater understanding of how PGP actually works. They have been doing this stuff forever. Presumably they are quite aware of the tradeoffs.