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Yubikey - Change To Super Combo Mode

In order for your YubiKey to be a U2F device and behave as a GPG card, you need to put the card into a mode called super combo mode. Since this is not the mode the card ships in, we need to change it. The way to do this is via the YubiKey Personalization Tool as shown below

Install the Yubikey personalization tool

sudo apt-get install yubikey-personalization -y

Change they key's mode:

sudo ykpersonalize -m 86

You should get some output like so:

Firmware version 4.3.7 Touch level 517 Program sequence 1

The USB mode will be set to: 0x86

Commit? (y/n) [n]: 

Enter y to commit.

Test This Worked

To test this worked, you can install the yubikey manager to check the status:

Install the manager:

sudo apt-get install yubikey-manager

Run the following command to get info:

ykman info

You should get some output like below:

Device type: YubiKey 4
Serial number: 6915790
Firmware version: 4.3.7
Enabled USB interfaces: OTP+FIDO+CCID

Applications
OTP         Enabled         
FIDO U2F    Enabled         
OpenPGP     Enabled         
PIV         Enabled         
OATH        Enabled         
FIDO2       Not available

You can also use:

ykman mode

... and you should see:

Current connection mode is: OTP+FIDO+CCID
Supported USB interfaces are: OTP, FIDO, CCID

References