diff --git a/doc/public_key_authentication.md b/doc/public_key_authentication.md
index a24c4cf..5a9055b 100644
--- a/doc/public_key_authentication.md
+++ b/doc/public_key_authentication.md
@@ -18,8 +18,8 @@ To enable PKA, the device must be initialized beforehand. In case the device has
To take advantage of PKA, the following is required:
1. Two Pico HSM: one will be used only for authentication (it can be any device able to generate a private key and sign arbitrary data).
-2. [SCS3](/doc/scs3.md "SCS3") tool to authenticate the user. At this time, OpenSC does not support PKA.
-3. A secret key of ECC 256 bits. SCS3 does not support other curves.
+2. [SCS3](/doc/scs3.md "SCS3") tool to authenticate the user. At this time, OpenSC does not support PKA, only initialization.
+3. A secret key of ECC 256 bits.
## Usage
@@ -29,35 +29,57 @@ Before using SCS3, it must be patched [scs3.patch.txt](https://github.com/polhen
On a secondary device, generate a private key, on the ECC 256 bits (`brainpoolP256r1` or `secp192r1`). Label it with an easy name, such as "Authentication".
-
+
Once finished, export the public key.
-
+
### Initialization
On the primary device, initialize it. When prompting for an authentication mechanism, select "Public Key Authentication".
-
+
Once finished, register the exported public key. A message of `0 authenticated public key(s) in 1 of 1 scheme` will appear if it is properly registered.
-
-
+
### Authentication
Plug the secondary device that stores the private key (do not load the device in the SCS3 tool) and initiate the public key authentication.
-
+
Select the secondary card and the Authentication private key (or the name you labeled it).
-
+
Introduce the PIN of the secondary device.
If the private key matches with the registered public key, the primary device will grant access and it will display `User PIN authenticated (9000)` (despite no PIN is provided).
From now on, you have full access and can operate normally with the primary device.
+
+## Notes on DKEK
+
+Pico HSM uses the PIN to protect the DKEK, which is lately used to protect private/secret keys and wrap/unwrap. However, when PKA is enabled, the authentication is not performed by introducing any PIN.
+Authenticated privileges are granted when PKA succeeds, regardless of PIN, which is optional.
+
+Nevertheless, *it is extremely recommended to combine PKA with PIN*. Note that when combined, only PKA grants authenticated privileges. Therefore, if both schemes are setup, it is necessary to unlock the DKEK with PIN verification.
+Otherwise, it will not be possible to operate with private/secret keys despite the user will be logged in.
+
+Unfortunately, SCS3 does not supports the combination of both schemes during the initialization. Fortunately, OpenSC does.
+
+To initialize the device with PKA *and* PIN use the following command (or similar), which accepts the use of PIN parameter *and* PKA configuration:
+
+```
+sc-hsm-tool -X --so-pin 1234567890123456 --pin 648219 -K 1 -n 1 -s 1
+```
+
+where PKA and PIN are enabled, jointly with DKEK protection.
+
+Therefore, with this scheme, multiple custodians may authenticate the device individually and, when fully authenticated, the master user can unlock the DKEK with the PIN.
+
+With this approach the device is kept safe and neither the DKEK nor the private/secret keys are stored in plain text in the device.
+Even though the flash memory is dumped by an attacker, it will not be possible to decipher any sensitive data or key.