{
  "$schema": "../../schema/test-vector.schema.json",
  "name": "Group Text Payload",
  "spec_ref": "src/08-payload-group.md",
  "protocol_version": 0,
  "description": "Tests group text message payload: channel_hash(1) + cipher_mac(2) + ciphertext. The encrypted plaintext is the GRP_TXT inner format: timestamp(4, LE) + flags(1) + \"<sender_name>: <body>\".",
  "vectors": [
    {
      "id": "grp-txt-001",
      "description": "Group text message with known channel secret",
      "type": "encode_decode",
      "structured": {
        "header": {
          "version": 0,
          "payload_type": "grp_txt",
          "route_type": "flood"
        },
        "path": {
          "hash_size": 1,
          "hash_count": 0,
          "hashes": []
        },
        "payload": {
          "channel_hash": "72",
          "cipher_mac": "EC1C",
          "ciphertext": "AE220A559CFF467B8F45948C2CABFD745BB36B14426A2127BB391DBBA51DE9E5"
        }
      },
      "binary": "15 00 72 EC1C AE220A559CFF467B8F45948C2CABFD745BB36B14426A2127BB391DBBA51DE9E5",
      "crypto_context": {
        "shared_secret": "202122232425262728292A2B2C2D2E2F303132333435363738393A3B3C3D3E3F",
        "encryption_key": "202122232425262728292A2B2C2D2E2F",
        "plaintext": "00F1536500616C6963653A2068656C6C6F206D657368"
      },
      "notes": "Channel hash = SHA256(channel_secret)[0] = 0x72. Inner plaintext is the GRP_TXT format: timestamp 1700000000 (00F15365 LE) + flags 0x00 (TXT_TYPE_PLAIN) + the message \"alice: hello mesh\" (sender name \"alice\"). 22 bytes, AES-128-ECB zero-padded to 32. AES key = first 16 bytes of channel secret; MAC = HMAC-SHA256(channel_secret, ciphertext)[0..1]."
    },
    {
      "id": "grp-txt-002",
      "description": "Group text with tampered MAC must fail",
      "type": "invalid",
      "binary": "15 00 72 0000 AE220A559CFF467B8F45948C2CABFD745BB36B14426A2127BB391DBBA51DE9E5",
      "expected_error": "mac_invalid",
      "notes": "Same ciphertext as grp-txt-001 but MAC zeroed. Verification must fail."
    }
  ]
}