You also need to have your private key on the Yubikey in order to be able to use it for signing. Please confirm that this is the case.

Hi,

Thank you for your reply.

Of course my cert is loaded insed my Yubikey :) It works perfectly with Outlook en EmMail.

Finally this mroning I found the problem myself. It comes from a buggy version of OpensSC. Now, using the 0.19 release it works well.

Thanks

Of course my cert is loaded insed my Yubikey :)

I did ask about your private key, not your cert. These are different things. You wouldn't necessarily need a Yubikey for just storing your cert, as there is nothing secret about the cert. Possibly among other things, the Yubikey is supposed to protect your private key.

Sorry the misunderstanding, i say Yes my private key is loaded. I said it works with Outlook not with Thunderbird :) If my private key was not loaded inside my Yubikey it would not have worked with other email Client :à)

Now it works with Thunderbird using the 0.19 release of OpenSC