A single source is represented sending a Torrential Downpour single source download.

One of the most litigated phrases in BitTorrent cases is some version of: “we downloaded the file from the defendant.” Defense counsel often responds with a fair, intuitive point: “BitTorrent downloads come from the swarm.”

Both statements can be true in different cases.

This post explains what single-source download claims are trying to establish, why they matter for attribution and distribution theories, and—most importantly—how to verify the claim against the actual artifacts instead of the affidavit’s summary.

If you’re new to the terminology, start with:

Ordinary BitTorrent behavior: multi-source by design

In normal BitTorrent operation, a client can request different pieces of the same content from multiple peers. That piece-swapping behavior is a core efficiency feature of the protocol [1].

That’s where the “swarm defense” comes from: if pieces can come from many peers, then “this IP participated” does not automatically mean “this IP was the exclusive source of the file.”

What “single-source download” is trying to mean in litigation

When an affidavit says “single-source download,” it usually aims to communicate something like:

  • The investigator restricted the download to one target IP:port, and
  • The retrieved data (or the complete file) came from that target peer rather than the swarm generally.

If true and documented, that can matter because it tends to reduce arguments like:

  • “It could have come from other peers,” and
  • “You can’t attribute the downloaded bytes to my client’s peer.”

It does not, by itself, solve identity of the person, but it can strengthen the link between the target peer and the transferred data.

How single-source downloads are achieved

Single-source downloads can be achieved through tool configuration (as with Torrential Downpour) or through network-level restrictions. For example, firewall rules can be used—even with conventional BitTorrent clients—to restrict connections so the client can only exchange data with a single target peer, effectively forcing a single-source download.

The key point for defense counsel: whether the restriction came from tool settings or firewall rules, the evidentiary question remains the same—what logs prove that only one peer was used as a source, and how was that verified?

A quiet but important detail: “single-source” is a settings claim

Treat “single-source” as shorthand for: “we set conditions that prevented other peers from being used as sources.”

That means your discovery and cross-exam should always include two linked questions:

  • What exact setting or control enforced exclusivity?
  • What artifact proves that control was actually applied during the specific session at issue?

Why defense counsel should verify the claim (not just argue it)

“Single-source” is often used as a shortcut phrase. But in practice, lawyers need to know which of these the evidence actually supports:

  • Single-source: the data was obtained from one target peer (as configured and proven by logs).
  • Single-peer: only one peer was observed during a session (not necessarily the only source).
  • Single-connection: one connection existed at a point in time (does not prove exclusive sourcing).

Those are not the same thing. Treating them as interchangeable is a common terminology trap.

What to demand in discovery (the artifacts that substantiate single-source)

If the government is using the phrase “single-source download,” ask for run artifacts that let you test it.

  • Run exports / session logs
    • The full export for the investigative session (not screenshots).
    • Target IP:port, start/end timestamps, time zone, and any session identifiers.
  • Peer selection and restriction evidence
    • Any configuration or run setting showing that sources were restricted to a single target peer.
    • Any logs showing connection attempts to other peers (or the absence thereof) and why.
  • Transfer records
    • Records of piece/block requests and responses.
    • Any summary that claims “downloaded from target” should have underlying detail.
  • Verification evidence
    • Proof that downloaded data was hash-verified (torrent piece verification, file hash verification, or tool-specific verification output).
  • Supporting TD artifacts
    • If produced in your case, request the “crown jewel” artifacts early: Datawritten.xml, downloadstatus.xml, details.txt, torrentinfo.txt, and netstat.txt.
    • Note: The exact names of these artifacts may vary based on which version of Torrential Downpour Receptor was used during the investigation. Ask the government to identify the version used and confirm the artifact names produced by that version.

For a quick guide to these artifacts and what to look for, see: Key Torrential Downpour log files.

A practical “sanity check” workflow (five minutes, high yield)

If you want a quick way to pressure-test the story before investing expert hours, do this:

  1. Pull the target IP:port and the exact session window from the affidavit.
  2. Check whether the production includes any raw session exports, not just narrative PDFs.
  3. Look for any evidence of peer discovery beyond the target (tracker/DHT activity) and how the tool allegedly prevented other sources.
  4. Look for transfer detail that ties blocks/pieces to the target endpoint, not just “downloaded from target” phrasing.
  5. Look for integrity verification beyond a conclusory sentence.

If any of those items is missing, you may have found the mismatch between “what the tool can do” and “what this case proves.”

One more practical tip: ask for the raw exports early, before anyone debates “what single-source means” in the abstract.

Cross-exam: single-source vs single-peer vs single-connection

Use questions that force definitions and point to the supporting record:

  • “When you say ‘single-source,’ do you mean the tool was configured to download only from one target IP:port?”
  • “Show me the configuration or log line that demonstrates source restriction.”
  • “Did the tool contact trackers or DHT during the session? If so, how did you prevent other peers from being used as sources?”
  • “Show me the piece transfer logs that tie the transferred bytes to the target IP:port.”
  • “Show me verification evidence that the data you received actually matched the alleged file.”

The goal is not to debate theory. The goal is to anchor the claim to artifacts.

The practical litigation point

Courts and judges often focus on whether:

  • Actual data was transferred, and
  • The data was verified (in a way consistent with the investigative narrative).

That’s why your best work is often “boring”: timestamps, target endpoint consistency, transfer detail, and verification.

Bottom line

Single-source download claims can meaningfully narrow “swarm ambiguity” when they are real, configured, and documented. They are also easy to overstate with loose terminology.

If your case turns on this issue, focus on the artifacts that prove (or fail to prove) exclusive sourcing and verification. If you want help translating tool output into a targeted request list or cross-exam outline, contact Lucid Truth Technologies using the LTT contact form: Contact.

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This article is for informational purposes and does not provide legal advice. Every case turns on specific facts and controlling law in your jurisdiction. Work with qualified counsel and, where appropriate, a qualified expert.

References

[1] B. Cohen, “The BitTorrent Protocol Specification (BEP 3),” BitTorrent.org, 2017. [Online]. Available: https://www.bittorrent.org/beps/bep_0003.html