Refactoring

src/contact.ts

@@ -0,0 +1,67 @@
+import { ecb } from '@noble/ciphers/aes.js';
+import { hmac } from '@noble/hashes/hmac.js';
+import { sha256 } from "@noble/hashes/sha2.js";
+import { BaseGroup, BaseGroupSecret, DecryptedGroupData, DecryptedGroupText, EncryptedPayload } from "./packet.types";
+import { BufferReader, equalBytes, hexToBytes } from "./parser";
+
+// The "Public" group is a special group that all nodes are implicitly part of. It uses a fixed secret derived from the string "Public".
+const publicSecret = hexToBytes("8b3387e9c5cdea6ac9e5edbaa115cd72");
+
+export class Group extends BaseGroup {}
+
+export class GroupSecret extends BaseGroupSecret {
+  public static fromName(name: string): GroupSecret {
+    if (name === "Public") {
+      return new GroupSecret(publicSecret);
+    } else if (!/^#/.test(name)) {
+      throw new Error("Only the 'Public' group or groups starting with '#' are supported");
+    }
+    const hash = sha256.create().update(new TextEncoder().encode(name)).digest();
+    return new GroupSecret(hash.slice(0, 16));
+  }
+
+  public decryptText(encrypted: EncryptedPayload): DecryptedGroupText {
+    const data = this.macThenDecrypt(encrypted.cipherMAC, encrypted.cipherText);
+    if (data.length < 8) {
+      throw new Error("Invalid ciphertext");
+    }
+
+    const reader = new BufferReader(data);
+    const timestamp = reader.readTimestamp();
+    const flags = reader.readByte();
+    const textType = (flags >> 2) & 0x3F;
+    const attempt = flags & 0x03;
+    const message = new TextDecoder('utf-8').decode(reader.readBytes());
+    return {
+      timestamp,
+      textType,
+      attempt,
+      message
+    }
+  }
+
+  public decryptData(encrypted: EncryptedPayload): DecryptedGroupData {
+    const data = this.macThenDecrypt(encrypted.cipherMAC, encrypted.cipherText);
+    if (data.length < 8) {
+      throw new Error("Invalid ciphertext");
+    }
+
+    const reader = new BufferReader(data);
+    return {
+      timestamp: reader.readTimestamp(),
+      data:      reader.readBytes(reader.remainingBytes())
+    };
+  }
+
+  private macThenDecrypt(cipherMAC: Uint8Array, cipherText: Uint8Array): Uint8Array {
+    const mac = hmac(sha256, this.secret, cipherText);
+    if (!equalBytes(mac, cipherMAC)) {
+      throw new Error("Invalid MAC");
+    }
+
+    const block = ecb(this.secret.slice(0, 16), { disablePadding: true });
+    const plain = block.decrypt(cipherText);
+
+    return plain;
+  }
+}