Handle invalid verified boot key (#55)

Treat the `verifiedBootKey` as null if it consists entirely of zero bytes, as some devices return this invalid value.

Additionally, this commit adds missing KDoc comments to the `AttestationData` class for better documentation.

app/src/main/java/org/matrix/TEESimulator/attestation/DeviceAttestationService.kt

@@ -43,6 +43,9 @@ object DeviceAttestationService {
      * @property attestVersion The attestation version (e.g., 400 for KeyMint 4.0).
      * @property keymasterVersion The Keymaster or KeyMint HAL version.
      * @property osVersion The Android OS version integer.
+     * @property osPatchLevel The Android security patch level (e.g., 202511).
+     * @property vendorPatchLevel The vendor-specific security patch level.
+     * @property bootPatchLevel The bootloader's security patch level.
      */
     data class AttestationData(
         val moduleHash: ByteArray?,
@@ -252,6 +255,10 @@ object DeviceAttestationService {
                 }
             }
 
+            if (verifiedBootKey?.all { it == 0.toByte() } == true) {
+                verifiedBootKey = null
+            }
+
             SystemLogger.info(
                 "Successfully extracted attestation data: version=$attestVersion, osVersion=$osVersion, osPatch=$osPatchLevel, vendorPatch=$vendorPatchLevel, bootPatch=$bootPatchLevel, moduleHash=${moduleHash?.toHex()}, bootKey=${verifiedBootKey?.toHex()}, bootHash=${verifiedBootHash?.toHex()}"
             )