GnuPG encryption with key file

[Peter Lebbing]

On 2014-03-27 14:35, David Shaw wrote:
> Limitations of the method

Plus that it has the same problems as

$ echo mysecret|gpg --passphrase-fd 0

That is, it ends up in your history if your shell keeps a history and 
you don't prevent it, and other users on a multi-user system can see the 
passphrase / the specific file used as a passphrase in the process list.

These issues wouldn't exist if GnuPG actually *supported* key files, 
and would prompt for the key file as it does for a passphrase. That's 
why I simply said "no", as in "it is not supported". But you can hack it 
together.

Also, key files easily lead to security-by-obscurity implementations 
where people think "an attacker doesn't know which file I use", whereas 
the attacker thinks "let's try all files, that's computationally 
feasible". But obviously that depends on the way you use it, it's just 
something to be aware of.

> it's not really using the binary file as a key, but rather as a 
> passphrase

I would consider this an advantage: the actual session key has good 
entropy, and the file is just used to encrypt the session key. Even if a 
"key file" would be properly supported by GnuPG, I would still prefer 
this two-step approach.

HTH,

Peter.

-- 
I use the GNU Privacy Guard (GnuPG) in combination with Enigmail.
You can send me encrypted mail if you want some privacy.
My key is available at 
<http://digitalbrains.com/2012/openpgp-key-peter>