api: add support for BIP85-derived BIP39 mnemonics

See
https://github.com/bitcoin/bips/blob/master/bip-0085.mediawiki#bip39.

Some of the other "apps" (derived secrets) using BIP-85 are not added
with this commit and may be added in the future. For now we add the
app that is probably used the most, which is deriving BIP-39
mnemonics.

The new protobuf messages are empty messages instead of reusing
e.g. the `Success {}` message so they can be extended in the future
without having to return different types of response
messages (e.g. Success OR a custom message).

CHANGELOG.md

@@ -9,6 +9,9 @@ customers cannot upgrade their bootloader, its changes are recorded separately.
 ### [Unreleased]
 - Improved security: keep seed encrypted in RAM
 
+### 9.15.0
+- Add support for deriving BIP-39 mnemonics according to BIP-85.
+
 ### 9.14.0
 - Improved touch button positional accuracy in noisy environments
 - Increased performance when signing Bitcoin transactions

CMakeLists.txt

@@ -88,8 +88,8 @@ endif()
 #
 # Versions MUST contain three parts and start with lowercase 'v'.
 # Example 'v1.0.0'. They MUST not contain a pre-release label such as '-beta'.
-set(FIRMWARE_VERSION "v9.14.1")
-set(FIRMWARE_BTC_ONLY_VERSION "v9.14.1")
+set(FIRMWARE_VERSION "v9.15.0")
+set(FIRMWARE_BTC_ONLY_VERSION "v9.15.0")
 set(BOOTLOADER_VERSION "v1.0.5")
 
 find_package(PythonInterp 3.6 REQUIRED)

messages/hww.proto

@@ -66,6 +66,7 @@ message Request {
         BTCRequest btc = 25;
         ElectrumEncryptionKeyRequest electrum_encryption_key = 26;
         CardanoRequest cardano = 27;
+        BIP85Request bip85 = 28;
     }
 }
 
@@ -87,5 +88,6 @@ message Response {
         BTCResponse btc = 13;
         ElectrumEncryptionKeyResponse electrum_encryption_key = 14;
         CardanoResponse cardano = 15;
+        BIP85Response bip85 = 16;
     }
 }

messages/keystore.proto

@@ -11,3 +11,9 @@ message ElectrumEncryptionKeyRequest {
 message ElectrumEncryptionKeyResponse {
   string key = 1;
 }
+
+message BIP85Request {
+}
+
+message BIP85Response {
+}

py/bitbox02/bitbox02/bitbox02/bitbox02.py

@@ -678,6 +678,15 @@ def electrum_encryption_key(self, keypath: Sequence[int]) -> str:
         )
         return self._msg_query(request).electrum_encryption_key.key
 
+    def bip85(self) -> None:
+        """Invokes the BIP-85 workflow on the device"""
+        self._require_atleast(semver.VersionInfo(9, 15, 0))
+
+        # pylint: disable=no-member
+        request = hww.Request()
+        request.bip85.CopyFrom(keystore.BIP85Request())
+        self._msg_query(request)
+
     def enable_mnemonic_passphrase(self) -> None:
         """
         Enable the bip39 passphrase.