Add Deeplink spec

docs/DEEPLINK.md

@@ -0,0 +1,97 @@
+## Abstract
+
+Boltcard NFC Programmer App is a native app on iOS and Android to flash or reset NTag424 into a Boltcard.
+
+1. The `Boltcard Service` generates the keys, and format them into a QR Code
+2. The user opens the Boltcard NFC Programmer, go to `Create Bolt Card`, scans the QR code
+3. The user then taps the card
+
+The QR code contains all the keys necessary for the app to create the Boltcard.
+
+Here are the shortcomings we aim to address in this specification:
+
+1. If the QR code is on the mobile device itself, it isn't possible to scan it
+2. It isn't possible to generate a pair of keys specific for the NTag424 being setup (the [deterministic key generation](./DETERMINISTIC.md) needs the UID before generating the keys)
+
+## Boltcard deeplinks
+
+The solution is for the `Boltcard Service` to generate deep links with the following format: `Boltcard://[program|reset]?url=[keys-request-url]`.
+
+When clicked, `Boltcard NFC Programmer` would open and either allow the user to program their NTag424 or reset it after asking for the NTags keys to the `keys-request-url`.
+
+The `Boltcard NFC Programmer` should send an HTTP POST request with `Content-Type: application/json` in the following format:
+
+```json
+{
+    "UID": "[UID]"
+}
+```
+
+Or
+
+```json
+{
+    "LNURLW": "lnurlw://..."
+}
+```
+
+In `curl`:
+
+```bash
+curl -X POST "[keys-request-url]" -H "Content-Type: application/json" -d '{"UID": "[UID]"}'
+```
+
+* `UID` needs to be 7 bytes. (Program action)
+* `LNURLW` needs to be read from the Boltcard's NDEF and can be sent in place of `UID`. It must contains the `p=` and `c=` arguments of the Boltcard. (Reset action)
+
+The response will be similar to the format of the QR code:
+
+```json
+{
+  "LNURLW": "lnurlw://...",
+  "K0":"[Key0]",
+  "K1":"[Key1]",
+  "K2":"[Key2]",
+  "K3":"[Key3]",
+  "K4":"[Key4]"
+}
+```
+
+## The Program action
+
+If `program` is specified in the Boltcard link, the `Boltcard NFC Programmer` must:
+
+1. Check if the lnurlw `NDEF` can be read.
+    * If the record can be read, then the card isn't reset, an error should be displayed to the user to first reset the Boltcard with the previous `Boltcard Service`.
+    * If the record can't be read, assume `K0` is `00000000000000000000000000000000` authenticate and call `GetUID` on the card again. (Since `GetUID` is called after authentication, the real `UID` will be returned even if `Random UID` has been activated)
+2. Send a request to the `keys-request-url` using the UID as explained above to get the NTag424 app keys
+3. Program the Boltcard
+
+## The Reset action
+
+If `reset` is specified in the Boltcard link, the `Boltcard NFC Programmer` must:
+1. Check if the lnurlw `NDEF` can be read.
+    * If the record can't be read, then the card is already reset, show an error message to the user.
+    * If the record can be read, continue to step 2.
+2. Send a request to the `keys-request-url` using the lnurlw as explained above to get the NTag424 app keys
+3. Reset the Boltcard to factory state
+
+## Handling setup/reset cycles for Boltcard Services
+
+When a NTag424 is reset, its counter is reset too.
+This means that if the user:
+
+* Setup a Boltcard
+* Make `5` payments
+* Reset the Boltcard
+* Setup the Boltcard on same `keys-request-url`
+
+With a naive implementation, the server will expect the next counter to be above `5`, but the next payment will have a counter of `0`.
+
+More precisely, the user will need to tap the card `5` times before being able to use the Boltcard for a payment successfully again.
+
+To avoid this issue the `Boltcard Service`, if using [Deterministic key generation](./DETERMINISTIC.md), should ensure it updates the key version during a `program` action.
+
+This can be done easily by the `Boltcard Service` by adding a parameter in the `keys-request-url` which specifies that the version need to be updated.
+
+When the `Boltcard NFC Programmer` queries the URL with the UID of the card, the `Boltcard Service` will detect this parameter, and update the version.

docs/TECHNOLOGY.md

@@ -5,6 +5,7 @@
 | [System](SYSTEM.md) | Bolt card system overview |
 | [Specification](SPEC.md) | Bolt card specifications |
 | [Deterministic Keys (DRAFT FOR COMMENT)](DETERMINISTIC.md) | Consideration about key generation |
+| [Boltcard Setup via Deeplink](DEEPLINK.md) | Deeplink for Boltcard creator apps |
 | [Privacy](CARD_PRIVACY.md) | Bolt card privacy |
 | [NXP 424 Datasheet](NT4H2421Gx.pdf) | NXP NTAG424DNA datasheet |
 | [NXP 424 Application Note](NT4H2421Gx.pdf) | NXP NTAG424DNA features and hints |