nixos-configurations/yubikey.md

Post-Rebuild YubiKey Setup Guide

Step 1: Generate GPG Master Key

gpg --expert --full-generate-key

At the prompts:

1. Select (9) ECC and ECC
2. Curve: Curve 25519
3. Expiration: 1y
4. Real name: 0xWheatyz
5. Email: wyatt@leeworks.dev
6. Set a strong passphrase

Note the key ID printed (e.g. 0x1234ABCD5678EFGH).

---

Step 2: Add Subkeys

gpg --expert --edit-key <KEY-ID>

Add 3 subkeys at the gpg> prompt:

Signing subkey:

gpg> addkey
→ (10) ECC (sign only)
→ Curve 25519
→ 1y expiry

Encryption subkey (may already exist — check with list):

gpg> addkey
→ (12) ECC (encrypt only)
→ Curve 25519
→ 1y expiry

Authentication subkey:

gpg> addkey
→ (11) ECC (set your own capabilities)
→ Toggle: disable Sign, enable Authenticate
→ Curve 25519
→ 1y expiry

gpg> save

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Step 3: Back Up Master Key (CRITICAL)

Once keys are moved to the YubiKey, they cannot be extracted. Back up now.

mkdir -p /tmp/gpg-backup
gpg --armor --export-secret-keys <KEY-ID> > /tmp/gpg-backup/master-secret.asc
gpg --armor --export-secret-subkeys <KEY-ID> > /tmp/gpg-backup/subkeys-secret.asc
gpg --armor --export <KEY-ID> > /tmp/gpg-backup/public.asc
gpg --export-ownertrust > /tmp/gpg-backup/ownertrust.txt

Copy /tmp/gpg-backup/ to an encrypted USB drive or other secure offline storage. Then remove the temp copy:

rm -rf /tmp/gpg-backup

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Step 4: Move Subkeys to YubiKey

gpg --edit-key <KEY-ID>

Move each subkey to its corresponding card slot:

gpg> key 1
gpg> keytocard
→ (1) Signature key
gpg> key 1

gpg> key 2
gpg> keytocard
→ (2) Encryption key
gpg> key 2

gpg> key 3
gpg> keytocard
→ (3) Authentication key

gpg> save

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Step 5: Set Trust & Verify

gpg --edit-key <KEY-ID>

gpg> trust
→ (5) I trust ultimately
gpg> quit

Verify the card:

gpg --card-status        # Should show all 3 subkeys
gpg --list-secret-keys   # Subkeys should show "ssb>" (stub pointing to card)

---

Step 6: Back Up & Remove Old SSH Keys

mkdir -p ~/.ssh/old
mv ~/.ssh/id_ed25519 ~/.ssh/old/
mv ~/.ssh/id_ed25519.pub ~/.ssh/old/

---

Step 7: Get Your New SSH Public Key

gpg --export-ssh-key <KEY-ID>

This outputs the SSH public key derived from your GPG auth subkey. Save it:

gpg --export-ssh-key <KEY-ID> > ~/.ssh/yubikey.pub

Verify gpg-agent serves it:

ssh-add -L   # Should show the same key

Deploy this key to your remote servers:

• vps (45.79.198.105) — add to ~/.ssh/authorized_keys for user wyatt
• home (10.0.0.20) — add to ~/.ssh/authorized_keys for user l-wyatt
• git (10.0.1.10) — add via your Gitea/Forgejo web UI
• GitHub — Settings → SSH and GPG Keys → New SSH Key

Tip: Use the old key (still in ~/.ssh/old/) to SSH in and deploy the new one:

ssh -i ~/.ssh/old/id_ed25519 vps "echo '$(gpg --export-ssh-key <KEY-ID>)' >> ~/.ssh/authorized_keys"

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Step 8: Update home.nix with Your Signing Key

Get your key ID:

gpg --list-secret-keys --keyid-format 0xlong

Then edit home.nix and replace the key = null; line:

signing = {
  key = "<YOUR-0xLONG-KEY-ID>";  # e.g. "0x1234ABCD5678EFGH"
  signByDefault = true;
};

Rebuild again:

nixos-rebuild switch

---

Step 9: Verify Everything

# Smartcard
gpg --card-status

# SSH via YubiKey
ssh-add -L
ssh vps echo "YubiKey SSH works!"

# Git signing
cd /tmp && git init test-sign && cd test-sign
git commit --allow-empty -m "test signing"
git log --show-signature -1
# Should show "Good signature from 0xWheatyz <wyatt@leeworks.dev>"
rm -rf /tmp/test-sign

---

Step 10 (Optional): Change YubiKey PINs

The default PINs are 123456 (user) and 12345678 (admin). Change them:

gpg --card-edit
gpg/card> admin
gpg/card> passwd
→ (1) Change PIN
→ (3) Change Admin PIN
gpg/card> quit

---

Step 11 (Optional): Upload GPG Public Key to GitHub

gpg --armor --export <KEY-ID>

Paste the output into GitHub → Settings → SSH and GPG Keys → New GPG Key. This makes your signed commits show "Verified" on GitHub.

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Note

The config changes to configuration.nix and home.nix are already saved. After you rebuild, reboot, and follow the steps above, you'll need to come back to update home.nix one more time with your actual GPG key ID (Step 8) and do a final rebuild.