Add key signing policy and key security info

content/keys.md

@@ -21,6 +21,98 @@ sub   ed25519/0x899C7CF4B526656F 2022-05-28 [A] [expires: 2022-11-24]
 
 You can download it [here](/pgp.asc) or from your preferred keyserver.
 
+<details>
+  <summary>
+    How I keep my private key safe
+  </summary>
+
+  ### Master key
+
+  My private master key is only used for the following purposes:
+
+  * Add or revoke UIDs
+  * Add or revoke subkeys
+  * Change expiry for subkeys or the master key itself
+  * Sign other keys
+
+  My private master key is only ever accessed on an airgapped machine,
+  with no internet or wireless communication capabilities, no camera or
+  microphone and no persistent storage. This airgapped machine is booted
+  with the latest version of [Tails OS](https://tails.boum.org). The
+  master key is protected by a long and secure passphrase and stored on
+  an encrypted storage medium, which itself is stored in a safe place.
+  
+  ### Subkeys
+
+  My subkeys are stored on an OpenPGP smartcard for daily use. The
+  smartcard makes sure that the local machine never has direct access to
+  the keys. It is protected by a pin-code and requires a physical touch
+  on every cryptographic operation.
+
+  ### Revocation and expiry
+
+  I usually set my master key to be valid for 2 years at a time. I will
+  always extend it at least 1 week prior to the expiry date. The same
+  goes for my subkeys, which are set to be valid for 6 months at a time.
+
+  If my keys are ever compromised, I have a revocation certificate,
+  stored in a safe, that I will publish to this website and various
+  keyservers.
+
+</details>
+
+<details>
+  <summary>
+    Key signing policy
+  </summary>
+
+  ### Certification levels
+
+  These are the certification levels I use to sign other keys, and the
+  requirements for each level.
+
+  #### Level 0: Generic verification (`sig`/`0x10`)
+  
+  This certification level is used if I have somehow verified that you
+  are in control of the email address(es) of the UID(s) to be signed.
+  No assertions are made about your identity.
+  
+  #### Level 1: No verification (`sig1`/`0x11`)
+  
+  This certification level is used when I have not safely verified you
+  as the keyholder, but I merely _believe_ that you own the key in
+  question.
+  
+  #### Level 2: Casual verification (`sig2`/`0x12`)
+  
+  This certification level is used when I have verified your identity
+  with at least one form of photo ID (government-issued or equally
+  secure), that your identity matches that of the UID(s) to be signed,
+  and that you are in control of the email address(es) of the UID(s) to
+  be signed.
+  
+  #### Level 3: Extensive verification (`sig3`/`0x13`)
+  
+  This certification level is used when I am _absolutely sure_ that you
+  are in fact the keyholder. This means that either you are someone I
+  know personally and trust, or that someone I ultimately trust have
+  notified me that you want a signature and have given me your key
+  fingerprint in a secure manner.
+
+  ### Signing process
+
+  The signing process consists of 2 steps:
+
+  1)  Verification will take place either in person or over video call.
+      If we meet in person, you will give me a physical copy of your key
+      fingerprint. If verification takes place over video call, you will
+      give me your key fingerprint verbally.
+  2)  You will have to send me your public key from the email address
+      associated with one of the UIDs to be signed. I will then sign the
+      key and send it back to the same email address in encrypted form.
+
+</details>
+
 ## SSH key
 
 If you need to give me shell access to your server or similar, please
@@ -30,4 +122,25 @@ use the following public SSH key:
 ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIPd/4fQV7CL8/KVwbo/phiV5UdXFBIDlkZ+ps8C7FeRf samsapti_yubikey_ssh
 ```
 
+<details>
+  <summary>
+    PGP signed version
+  </summary>
+
+  ```txt
+  -----BEGIN PGP SIGNED MESSAGE-----
+  Hash: SHA512
+
+  ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIPd/4fQV7CL8/KVwbo/phiV5UdXFBIDlkZ+ps8C7FeRf samsapti_yubikey_ssh
+
+  -----BEGIN PGP SIGNATURE-----
+
+  iHUEARYKAB0WIQR1jxoXyANf2TkSyeLLu+c3HoHE6gUCYqeuFwAKCRDLu+c3HoHE
+  6tTqAQDhUokTzNxn4h06UKCbggtTG3EpMrbgNT2HUQugpD6t7gEA6IleDY/aubyT
+  Giy/YDkzUoJlVghNq0rU+DcSC1dLzQs=
+  =FjyX
+  -----END PGP SIGNATURE-----
+  ```
+</details>
+
 You can download it [here](/ssh.pub).