This is a guide to using [YubiKey](https://www.yubico.com/products/) as a [smart card](https://security.stackexchange.com/questions/38924/how-does-storing-gpg-ssh-private-keys-on-smart-cards-compare-to-plain-usb-drives) for secure encryption, signature and authentication operations.
This is a guide to using [YubiKey](https://www.yubico.com/products/identifying-your-yubikey/) as a [smart card](https://security.stackexchange.com/questions/38924/how-does-storing-gpg-ssh-private-keys-on-smart-cards-compare-to-plain-usb-drives) for secure encryption, signature and authentication operations.
Keys stored on YubiKey are [non-exportable](https://web.archive.org/web/20201125172759/https://support.yubico.com/hc/en-us/articles/360016614880-Can-I-Duplicate-or-Back-Up-a-YubiKey-), unlike filesystem-based credentials, while remaining convenient for daily use. YubiKey can be configured to require a physical touch for cryptographic operations, reducing the risk of credential compromise.
By default, YubiKey will perform cryptographic operations without requiring any action from the user after the key is unlocked once with the PIN.
To require a touch for each key operation, use [YubiKey Manager](https://developers.yubico.com/yubikey-manager/) and the Admin PIN to set key policy.
@ -1997,16 +1995,16 @@ EOF
- To get more information on potential errors, restart the `gpg-agent` process with debug output to the console with `pkill gpg-agent; gpg-agent --daemon --no-detach -v -v --debug-level advanced --homedir ~/.gnupg`.
- If you encounter problems connecting to YubiKey with GnuPG - try unplugging and re-inserting YubiKey, and restarting the `gpg-agent` process.
- If you see `General key info..: [none]` in card status output - import the public key.
- If you receive the error, `gpg: decryption failed: secret key not available` - you likely need to install GnuPG version 2.x. Another possibility is that there is a problem with the PIN, e.g., it is too short or blocked.
- A lot of issues can be fixed by unplugging and re-inserting YubiKey, or restarting the `gpg-agent` process.
- If you receive the error, `Yubikey core error: no yubikey present` - make sure the YubiKey is inserted correctly. It should blink once when plugged in.
- If you still receive the error, `Yubikey core error: no yubikey present` - you likely need to install newer versions of yubikey-personalize as outlined in [Install software](#install-software).
- If you see `General key info..: [none]` in card status output - import the public key.
- If you receive the error, `gpg: decryption failed: secret key not available` - you likely need to install GnuPG version 2.x. Another possibility is that there is a problem with the PIN, e.g., it is too short or blocked.
- If you receive the error, `Yubikey core error: write error` - YubiKey is likely locked. Install and run yubikey-personalization-gui to unlock it.
- If you receive the error, `Key does not match the card's capability` - you likely need to use 2048-bit RSA key sizes.
@ -2025,7 +2023,7 @@ EOF
- If you receive the error, `Permission denied (publickey)`, increase ssh verbosity with the `-v` flag and verify the public key from the card is being offered: `Offering public key: RSA SHA256:abcdefg... cardno:00060123456`. If it is, verify the correct user the target system - not the user on the local system. Otherwise, be sure `IdentitiesOnly` is not [enabled](https://github.com/FiloSottile/whosthere#how-do-i-stop-it) for this host.
- If SSH authentication still fails - add up to 3 `-v` flags to the `ssh` client to increase verbosity.
- If SSH authentication still fails - add up to 3 `-v` flags to the `ssh` command to increase verbosity.
- If it still fails, it may be useful to stop the background `sshd` daemon process service on the server (e.g. using `sudo systemctl stop sshd`) and instead start it in the foreground with extensive debugging output, using `/usr/sbin/sshd -eddd`. Note that the server will not fork and will only process one connection, therefore has to be re-started after every `ssh` test.
drduh
1 month ago