refactor(core,keys): BIP-39's English list moves into halkyon_core

The list a recovery phrase's words are of moves from halkyon_keys into
halkyon_core, exported as bip39English, so that the server module can
take a waiting account's matching code from it (Halkyon Learn's ADR
0021, D33) without depending on halkyon_keys and libsodium. Its test
(2048 words, sorted, the published file's SHA-256, unique by their first
four letters) moves along; its MIT licence too.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

packages/halkyon_core/BIP39-LICENSE

@@ -0,0 +1,26 @@
+The English word list in lib/src/bip39_english.dart is BIP-39's
+(https://github.com/bitcoin/bips/blob/master/bip-0039/english.txt), by Marek
+Palatinus, Pavol Rusnak, Aaron Voisine and Sean Bowe, 2013. BIP-39 falls under
+the MIT License:
+
+MIT License
+
+Copyright (c) 2013 Marek Palatinus, Pavol Rusnak, Aaron Voisine, Sean Bowe
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

packages/halkyon_core/lib/halkyon_core.dart

@@ -6,6 +6,8 @@
 /// - A `Logger` interface and basic `ConsoleLogger` implementation.
 /// - The optional `HalkyonException` marker interface.
 /// - `SerialQueue` and `CoalescingRunner`, which run work one at a time.
+/// - BIP-39's English word list (`bip39English`), which a recovery phrase's
+///   words and an account's matching code are of.
 library;
 
 // Re-export the clock package directly. Halkyon apps depend on `Clock` for
@@ -15,6 +17,7 @@ export 'package:clock/clock.dart' show Clock, clock;
 
 export 'src/async/coalescing_runner.dart';
 export 'src/async/serial_queue.dart';
+export 'src/bip39_english.dart';
 export 'src/exceptions.dart';
 export 'src/logger.dart';
 export 'src/uuid.dart';

packages/halkyon_core/pubspec.yaml

@@ -12,4 +12,6 @@ dependencies:
   uuid: ^4.5.0
 
 dev_dependencies:
+  # SHA-256, which the BIP-39 list is checked against.
+  crypto: ^3.0.7
   test: ^1.25.0

packages/halkyon_core/test/bip39_english_test.dart

@@ -0,0 +1,26 @@
+import 'package:crypto/crypto.dart';
+import 'package:halkyon_core/halkyon_core.dart';
+import 'package:test/test.dart';
+
+void main() {
+  test("the word list is BIP-39's English list: 2,048 words, sorted, each "
+      'once', () {
+    expect(bip39English, hasLength(2048));
+    expect(bip39English.toSet(), hasLength(2048));
+    expect([...bip39English]..sort(), bip39English);
+    // The SHA-256 of english.txt, a word a line.
+    expect(
+      sha256.convert('${bip39English.join('\n')}\n'.codeUnits).toString(),
+      '2f5eed53a4727b4bf8880d8f3f199efc90e58503646d9ff8eff3a2ed3b24dbda',
+    );
+  });
+
+  test('no two words begin with the same four letters', () {
+    expect(
+      bip39English
+          .map((word) => word.substring(0, word.length.clamp(0, 4)))
+          .toSet(),
+      hasLength(2048),
+    );
+  });
+}

packages/halkyon_keys/README.md

@@ -57,10 +57,11 @@ phrase.
 
 `dart test`: libsodium's own Argon2id known answers (its `pwhash_argon2id` test, so the
 compiled libsodium is the one these keys were made with), BIP-39's English vectors
-(trezor/python-mnemonic's `vectors.json`, MIT), the word list's SHA-256, round trips,
-and every refusal.
+(trezor/python-mnemonic's `vectors.json`, MIT), round trips, and every refusal; the
+word list's SHA-256 is checked in halkyon_core.
 
 ## Licence
 
 GNU Affero General Public License, version 3 or any later version (`LICENSE`). The
-English word list is BIP-39's, under the MIT License (`BIP39-LICENSE`).
+English word list is BIP-39's, in halkyon_core, under the MIT License (its
+`BIP39-LICENSE`).

packages/halkyon_keys/lib/src/recovery_phrase.dart

@@ -1,7 +1,7 @@
 import 'dart:typed_data';
 
 import 'package:crypto/crypto.dart';
-import 'package:halkyon_keys/src/bip39_english.dart';
+import 'package:halkyon_core/halkyon_core.dart' show bip39English;
 import 'package:halkyon_keys/src/key_refused.dart';
 import 'package:sodium/sodium_sumo.dart';
 

packages/halkyon_keys/pubspec.yaml

@@ -14,6 +14,9 @@ environment:
 dependencies:
   # SHA-256, which BIP-39's checksum is made with.
   crypto: ^3.0.7
+  # BIP-39's English list, which the recovery phrase's words are of.
+  halkyon_core:
+    path: ../halkyon_core
   # libsodium's API (Argon2id, X25519, Ed25519, XChaCha20-Poly1305, sealed
   # boxes, the KDF), pinned exactly: what keys an account's data must never
   # move by accident. Its build hook compiles libsodium 1.0.22 from the source

packages/halkyon_keys/test/recovery_phrase_test.dart

@@ -1,8 +1,6 @@
 import 'dart:typed_data';
 
-import 'package:crypto/crypto.dart';
 import 'package:halkyon_keys/halkyon_keys.dart';
-import 'package:halkyon_keys/src/bip39_english.dart';
 import 'package:sodium/sodium_sumo.dart';
 import 'package:test/test.dart';
 
@@ -21,18 +19,6 @@ Future<void> main() async {
     isA<KeyRefused>().having((refused) => refused.reason, 'reason', reason),
   );
 
-  test("the word list is BIP-39's English list: 2,048 words, sorted, each "
-      'once', () {
-    expect(bip39English, hasLength(2048));
-    expect(bip39English.toSet(), hasLength(2048));
-    expect([...bip39English]..sort(), bip39English);
-    // The SHA-256 of english.txt, a word a line.
-    expect(
-      sha256.convert('${bip39English.join('\n')}\n'.codeUnits).toString(),
-      '2f5eed53a4727b4bf8880d8f3f199efc90e58503646d9ff8eff3a2ed3b24dbda',
-    );
-  });
-
   group("BIP-39's English test vectors (trezor/python-mnemonic)", () {
     for (final (entropy, mnemonic) in bip39Vectors) {
       test(mnemonic.split(' ').take(3).join(' '), () {