feat: implement end-to-end encryption for relay connections

packages/relay/src/base64.ts

@@ -0,0 +1,12 @@
+import { fromByteArray, toByteArray } from "base64-js";
+
+export function arrayBufferToBase64(buffer: ArrayBuffer): string {
+  return fromByteArray(new Uint8Array(buffer));
+}
+
+export function base64ToArrayBuffer(base64: string): ArrayBuffer {
+  const bytes = toByteArray(base64);
+  const out = new Uint8Array(bytes.byteLength);
+  out.set(bytes);
+  return out.buffer;
+}

packages/relay/src/crypto.ts

@@ -1,3 +1,4 @@
+/// <reference lib="dom" />
 /**
  * E2EE crypto primitives using WebCrypto API.
  *
@@ -6,6 +7,8 @@
  * - AES-256-GCM for authenticated encryption
  */
 
+import { arrayBufferToBase64, base64ToArrayBuffer } from "./base64.js";
+
 const ECDH_ALGORITHM = { name: "ECDH", namedCurve: "P-256" };
 const AES_ALGORITHM = { name: "AES-GCM", length: 256 };
 const IV_LENGTH = 12;
@@ -127,23 +130,3 @@ export async function decrypt(
     return plaintext;
   }
 }
-
-// --- Helpers ---
-
-function arrayBufferToBase64(buffer: ArrayBuffer): string {
-  const bytes = new Uint8Array(buffer);
-  let binary = "";
-  for (let i = 0; i < bytes.byteLength; i++) {
-    binary += String.fromCharCode(bytes[i]);
-  }
-  return btoa(binary);
-}
-
-function base64ToArrayBuffer(base64: string): ArrayBuffer {
-  const binary = atob(base64);
-  const bytes = new Uint8Array(binary.length);
-  for (let i = 0; i < binary.length; i++) {
-    bytes[i] = binary.charCodeAt(i);
-  }
-  return bytes.buffer;
-}

packages/relay/src/encrypted-channel.ts

@@ -1,3 +1,4 @@
+/// <reference lib="dom" />
 /**
  * Encrypted channel that wraps a WebSocket-like transport.
  *
@@ -13,6 +14,7 @@ import {
   encrypt,
   decrypt,
 } from "./crypto.js";
+import { arrayBufferToBase64, base64ToArrayBuffer } from "./base64.js";
 
 export interface Transport {
   send(data: string | ArrayBuffer): void;
@@ -193,23 +195,3 @@ export class EncryptedChannel {
     return this.state === "open";
   }
 }
-
-// --- Helpers ---
-
-function arrayBufferToBase64(buffer: ArrayBuffer): string {
-  const bytes = new Uint8Array(buffer);
-  let binary = "";
-  for (let i = 0; i < bytes.byteLength; i++) {
-    binary += String.fromCharCode(bytes[i]);
-  }
-  return btoa(binary);
-}
-
-function base64ToArrayBuffer(base64: string): ArrayBuffer {
-  const binary = atob(base64);
-  const bytes = new Uint8Array(binary.length);
-  for (let i = 0; i < binary.length; i++) {
-    bytes[i] = binary.charCodeAt(i);
-  }
-  return bytes.buffer;
-}