copy nip44 code from chebizarro/dart-nip44

packages/ndk/lib/shared/nips/nip44/nip44.dart

@@ -0,0 +1,105 @@
+import 'dart:convert';
+import 'dart:typed_data';
+import 'package:elliptic/ecdh.dart';
+import 'package:elliptic/elliptic.dart';
+import 'utils.dart';
+
+/// NIP-44 encryption and decryption functions.
+class Nip44 {
+  static Future<String> encryptMessage(
+    String plaintext,
+    String senderPrivateKey,
+    String recipientPublicKey, {
+    Uint8List? customNonce,
+    Uint8List? customConversationKey,
+  }) async {
+    // Step 1: Compute Shared Secret
+    final sharedSecret = customConversationKey ??
+        computeSharedSecret(senderPrivateKey, recipientPublicKey);
+
+    // Step 2: Derive Conversation Key
+    final conversationKey =
+        customConversationKey ?? deriveConversationKey(sharedSecret);
+
+    // Step 3: Generate or Use Custom Nonce
+    final nonce = customNonce ?? secureRandomBytes(32);
+
+    // Step 4: Derive Message Keys
+    final keys = deriveMessageKeys(conversationKey, nonce);
+    final chachaKey = keys['chachaKey']!;
+    final chachaNonce = keys['chachaNonce']!;
+    final hmacKey = keys['hmacKey']!;
+
+    // Step 5: Pad Plaintext
+    final paddedPlaintext = pad(utf8.encode(plaintext));
+
+    // Step 6: Encrypt
+    final ciphertext =
+        await encryptChaCha20(chachaKey, chachaNonce, paddedPlaintext);
+
+    // Step 7: Calculate MAC
+    final mac = calculateMac(hmacKey, nonce, ciphertext);
+
+    // Step 8: Construct Payload
+    return constructPayload(nonce, ciphertext, mac);
+  }
+
+  static Future<String> decryptMessage(
+    String payload,
+    String recipientPrivateKey,
+    String senderPublicKey, {
+    Uint8List? customConversationKey,
+  }) async {
+    // Step 1: Compute Shared Secret
+    final sharedSecret = customConversationKey ??
+        computeSharedSecret(recipientPrivateKey, senderPublicKey);
+
+    // Step 2: Derive Conversation Key
+    final conversationKey =
+        customConversationKey ?? deriveConversationKey(sharedSecret);
+
+    // Step 3: Parse Payload
+    final parsed = parsePayload(payload);
+    final nonce = parsed['nonce'];
+    final ciphertext = parsed['ciphertext'];
+    final mac = parsed['mac'];
+
+    // Step 4: Derive Message Keys
+    final keys = deriveMessageKeys(conversationKey, nonce);
+    final chachaKey = keys['chachaKey']!;
+    final chachaNonce = keys['chachaNonce']!;
+    final hmacKey = keys['hmacKey']!;
+
+    // Step 5: Verify MAC
+    verifyMac(hmacKey, nonce, ciphertext, mac);
+
+    // Step 6: Decrypt
+    final paddedPlaintext =
+        await decryptChaCha20(chachaKey, chachaNonce, ciphertext);
+
+    // Step 7: Unpad Plaintext
+    final plaintextBytes = unpad(paddedPlaintext);
+
+    return utf8.decode(plaintextBytes);
+  }
+
+  static Uint8List computeSharedSecret(String privateKeyHex, String publicKeyHex) {
+    final ec = getS256();
+    final privateKey = PrivateKey.fromHex(ec, privateKeyHex);
+    final publicKey =
+        PublicKey.fromHex(ec, checkPublicKey(publicKeyHex));
+    final sec = computeSecret(privateKey, publicKey);
+    return Uint8List.fromList(sec);
+  }
+
+  static Uint8List deriveConversationKey(Uint8List sharedSecret) {
+    final salt = utf8.encode('nip44-v2');
+
+    final conversationKey = hkdfExtract(
+      ikm: sharedSecret,
+      salt: Uint8List.fromList(salt),
+    );
+
+    return conversationKey;
+  }
+}