Most efficient way to look whether a secret key is for X.509 or for OpenPGP

[Andre Heinecke]

Hi

On Thursday 3 January 2019 02:04:38 CET Rainer Perske wrote:
> I use gpgsm and gpg2 concurrently. I can quickly and easily see whether
> there are private keys in gnupghome/private-keys-v1.d/. But I cannot
> easily see whether these keys belong to X.509 key pairs or to OpenPGP
> key pairs.
> 
> For my application, I need to know:
> 
> a) What is the fastest way to detect whether I have a private X.509
>    key? I need a simple boolean answer: yes or no.
> ....

My idea to make it faster then letting the agent do it is to do a keylisting 
with the keygrip:

gpg(sm) --with-colons -k --with-keygrip
(the grp line contains the keygrip)

And then check if the private-keys.v1.d contains such a key file.This would be 
quicker of course if you only needed to check for the private key of a specific 
pubkey for which you knew the keyrgrip in advance.

You should leave it to the agent though (maybe you could somehow prestart the 
agent to make it faster)? So that it is more robust if the key format changes 
in the future.

Regards,
Andre

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