On Friday, February 19, 2016 at 2:28:51 PM UTC-6, Thiago de Arruda wrote:
> 
> If the encrypted file is stored in a shared server(or alternatives suggested 
> by @atoponce: Dropbox, Google Drive, NFS, Samba shares) a sysadmin could 
> brute force a weak password since Vim uses sha256 as KDF. Then it would 
> simply be a matter of encrypting the desired code(eg: an uncovered modeline 
> bug) and replacing the real ciphertext with the fabricated one. When the user 
> restores the backup on his own machine and decrypts the file, the code would 
> execute since there's no MAC validation)
> 

Except, if the nefarious admin has brute-forced the password to re-encrypt with 
desired modifications, then they'll just recalculate the MAC as well, right? So 
MAC wouldn't help for this attack. Better KDF for sure, though; we can't expect 
everyone to use 100+ bits of entropy in a password :-)

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