Modern gnupg.conf setup

[Damien Goutte-Gattat]

On Sat, Dec 14, 2019 at 11:18:32PM +0100, Defiant wrote:
>Hey, I recall back in the days there were lots of online tutorials about
>how to strengthen your GnuPG configuration.

I don’t know which tutorials exactly you’re referring to, but I have 
seen several of them myself, and I have always had the feeling that they 
were written by people who couldn’t be bothered to check what GnuPG’s 
default configuration actually is before deciding it needed to be 
”strengthened”…


>no-emit-version
>no-comments

Not needed, those are the defaults.


>export-options export-minimal

That’s up to you. Note, this does not actually “strengthen” anything.


>keyid-format 0xlong
>with-fingerprint

For information, the default is not to display any key ID (either short 
or long) but to display the full fingerprint instead (which makes 
displaying the key ID quite irrelevant).

Setting keyid-format to either “short” or “long” however has the effect 
of forcing GnuPG to display the key ID of *subkeys*, so if that’s 
something you need, you may keep that line.


>list-options show-uid-validity
>verify-options show-uid-validity

Already enabled by default.


>personal-cipher-preferences AES256

The default is AES256, AES192, AES128, 3DES. Note that you cannot remove 
3DES which is mandatory as per the RFC 4880 (that’s the only algorithm 
which is guaranteed to be supported by any compliant OpenPGP 
implementation): even if you do not include it, GnuPG will silently add 
it back.

By removing AES192 and AES128, you’re actually increasing the risk that 
GnuPG will have to fallback to 3DES if AES256 is not supported by the 
other party. I don’t think this is what you want.


>personal-digest-preferences SHA512

The default is SHA256, SHA384, SHA512, SHA-224, SHA1, with SHA1 being 
mandatory. Same problem as above: by limiting GnuPG’s options, you are 
increasing the risk of having to fallback to SHA1.


>default-preference-list SHA512 SHA384 SHA256 SHA224 AES256 AES192 AES
>TWOFISH ZLIB BZIP2 ZIP Uncompressed

This is almost exactly the default list, except that the default list 
does not include TWOFISH.


>cipher-algo AES256
>digest-algo SHA512
>cert-digest-algo SHA512
>compress-algo ZLIB

You are basically bypassing the whole preference-based mechanism used to 
select algorithms compatible with your recipients’ implementation.  
Almost certainly a bad idea unless you are operating in a context where 
you know you don’t need to care about interoperability (e.g. if you are 
only encrypting files for yourself).


>disable-cipher-algo 3DES IDEA CAST5 Blowfish
>weak-digest SHA1

3DES and SHA1 are mandatory as said above. The other algorithms are 
already not used by default.


>s2k-cipher-algo AES256
>s2k-digest-algo SHA512
>s2k-mode 3
>s2k-count 65011712

The default S2K mode is already 3 (iter+salt). As for the S2K count, for 
information the default is a value automatically determined by GPG Agent 
so that, on your computer, running the S2K algorithm will take ~100ms.


Overall I’d say most of your configuration is either uneeded or even 
counterproductive. I’ll quote GnuPG’s FAQ [1]:

> Does GnuPG need to be ‘tuned’ before use?
> No. GnuPG has sensible defaults right out of the box.


Cheers,

- Damien


[1] https://gnupg.org/faq/gnupg-faq.html#tuning
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