Change from 4MB chunk data to blend in with other traffic?

Development
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A few years back I’ve heard a talk by someone from the Tor Onion team, they talked about difficulties getting around example China’s great firewall. They tried to make the traffic look like other common traffic so it would blend in and not get caught.

From what I think I’ve remember Tor went with 1MB chunk size and did some other tricks to make data look like other ordinary data. I wonder if that is something that the devs have thought about or not? Should Autonomi take this question into consideration? @rusty.spork @dirvine @JimCollinson @Bux

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Tor doesn’t have a “chunk size”. The idea doesn’t even make sense in the context of Tor.

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Yes, Tor does involve data chunking, particularly in how it handles circuit-level communication. Here’s an overview of Tor’s data chunking:

  • Cell Size: Tor uses fixed-size cells for communication through its network. The standard cell size in Tor is 512 bytes. Each cell contains a relay header and payload. This fixed size helps in maintaining anonymity by making traffic patterns harder to distinguish.

  • Purpose of Fixed Size:

    • Anonymity: Fixed-size cells make it difficult for observers to correlate traffic patterns with specific activities, enhancing privacy.
    • Efficiency: Using cells of a fixed size simplifies the handling of data both in terms of processing and transmission over the network.

  • Handling of Data:

    • When data is sent through Tor, it’s broken down into these 512-byte cells. If the data is less than 512 bytes, padding is added to fill out the cell. If the data exceeds this size, it’s split across multiple cells.
    • The cells are used not only for data but also for control information like setting up circuits, extending them, and other circuit management functions.

  • Data Fragmentation:

    • For larger data transfers or streams, data might be fragmented or chunked into these cells before being relayed through the network. This chunking ensures that no single packet or cell contains enough information to reveal the entire content or the nature of the communication, thereby aiding in maintaining the anonymity of the traffic.

  • Protocol Specifications:

    • The Tor protocol specifications, as outlined in documents like tor-spec.txt, detail how these cells are structured, including the use of variable length cells for certain control messages, but the core data transmission still revolves around the 512-byte cell size.

  • Security Considerations:

    • The fixed size and method of chunking data in Tor are part of its security design. By ensuring that all data is processed in uniform packets, it reduces the information leakage that could occur from varying packet sizes, which might otherwise reveal information about the type or source of the data.

Understanding Tor’s chunk size is crucial for developers or users looking into how Tor maintains anonymity through packet uniformity and for those interested in the technical underpinnings of privacy-preserving technologies.

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