How the Created by Field Identifies Torrent Software

This article explains how the “created by” field inside a .torrent file functions as an informational metadata tag that identifies the specific software application and version used to author the file. It explores the underlying Bencoded dictionary structure of torrent files, details how BitTorrent clients write and parse this specific string, and examines why this field is an optional, modifiable identifier that exists outside the core cryptographic data.

The Structure of Torrent Files and Bencoding

Every .torrent file is a structured container encoded using a serialization format known as Bencoding. Bencoding supports four basic data types: integers, byte strings, lists, and dictionaries (key-value maps).

At the root level of a .torrent file sits a master dictionary containing several standard keys defined by the BitTorrent specification (BEP 0003), such as announce, info, and optionally creation date and created by.

How the “created by” Field Operates

When a user creates a new torrent using a client or command-line utility (such as qBittorrent, Transmission, or mktorrent), the application automatically injects a top-level key named created by into the root dictionary.

The value associated with this key is a standard Bencoded text string containing the application’s identifier. The format typically includes the application name followed by the version number.

For example, in raw Bencoded format, the key-value pair appears like this:

10:created by18:qBittorrent v4.6.0

In this raw representation: * 10:created by defines a string key with a length of 10 characters (created by). * 18:qBittorrent v4.6.0 defines the corresponding string value with a length of 18 characters (qBittorrent v4.6.0).

How Software Reads the Identifier

When any BitTorrent client, torrent parser, or indexing service opens a .torrent file, it performs the following steps to identify the generating software:

  1. Decoding: The parser reads the raw binary data and decodes the root Bencoded dictionary into memory.
  2. Key Lookup: The software searches the top-level keys for the string created by.
  3. Extraction: If present, the parser reads the string value directly and displays it in the user interface under the torrent’s general metadata or properties panel.

Significance Outside the Info Hash

The created by field resides in the root dictionary, not inside the info dictionary.

The info dictionary contains the critical file data, piece lengths, and SHA-1 hashes used to verify data integrity and generate the unique Info Hash identifier of the torrent. Because created by is located outside the info dictionary, modifying, removing, or spoofing the created by string will not alter the torrent’s Info Hash or disrupt peer-to-peer downloading.

Reliability and Customization

According to the official BitTorrent specification, the created by field is entirely optional. Some software tools allow users to leave the field blank for privacy or replace it with custom text, such as a website URL or organization name. Consequently, while the field generally provides an accurate indicator of the authoring client, it is purely descriptive metadata and cannot be used as an immutable cryptographic proof of origin.