chore(repo): initialize WebDrop monorepo

Signed-off-by: JustMe <mr.toing@outlook.com>

packages/core/src/internal.ts

@@ -0,0 +1,42 @@
+/**
+ * 仅供测试和调试:把通常不可导出的中间密钥以字节形式导出,用来和测试向量逐字节比对。
+ * 正常使用请只依赖主入口。这里的函数会让密钥材料暴露在 JS 变量里,不要在产品代码中使用。
+ */
+
+import { Labels } from './constants.js';
+import { utf8, type Bytes } from './bytes.js';
+
+export { encodeEnvelope, frameAad, frameIv, padPlaintext, parseEnvelope, sealFrame, tierFor, unpadPlaintext } from './frame.js';
+export { encodeMeta, decodeFirstFrame, planEncItem, planRawItem } from './item.js';
+export { deriveChannelKeys, deriveItemKey, deriveOwnerToken, sha256 } from './kdf.js';
+
+async function hkdfBytes(ikm: Uint8Array, salt: Uint8Array, label: string): Promise<Bytes> {
+  const key = await globalThis.crypto.subtle.importKey('raw', ikm as Bytes, 'HKDF', false, ['deriveBits']);
+  const bits = await globalThis.crypto.subtle.deriveBits(
+    { name: 'HKDF', hash: 'SHA-256', salt: salt as Bytes, info: utf8(label) },
+    key,
+    256,
+  );
+  return new Uint8Array(bits);
+}
+
+export interface RawChannelSecrets {
+  kEnc: Bytes;
+  tRead: Bytes;
+  tWrite: Bytes;
+  kLabel: Bytes;
+}
+
+export async function deriveRawChannelSecrets(channelId: Uint8Array, k: Uint8Array): Promise<RawChannelSecrets> {
+  const kEnc = await hkdfBytes(k, channelId, Labels.enc);
+  return {
+    kEnc,
+    tRead: await hkdfBytes(k, channelId, Labels.read),
+    tWrite: await hkdfBytes(k, channelId, Labels.write),
+    kLabel: await hkdfBytes(kEnc, channelId, Labels.label),
+  };
+}
+
+export const deriveRawOwnerToken = (channelId: Uint8Array, a: Uint8Array): Promise<Bytes> => hkdfBytes(a, channelId, Labels.owner);
+
+export const deriveRawItemKey = (kEnc: Uint8Array, itemId: Uint8Array): Promise<Bytes> => hkdfBytes(kEnc, itemId, Labels.item);