A file with a fingerprint and hash, related to the Torrential Downpour hash value probable cause.

In many BitTorrent investigations, the affidavit includes a claim that looks almost mathematical: “This hash value is a known file.” That claim is often used to support probable cause without a human opening the file first.

This post explains what that claim means, why it can be powerful, and where it can go wrong. It also gives defense counsel a practical checklist for validating the affidavit’s language against the underlying technical records.

What a hash is (and what it is not)

A cryptographic hash function takes input data and produces a fixed-length output. The output is often called a digest or hash value. For example, the SHA family of hash functions is standardized by NIST [1].

In plain English, a hash is useful because:

  • If the input changes, the hash should change.
  • The same input should produce the same hash every time.

However, a hash is not:

  • A “fingerprint of the person.” It identifies data, not the user.
  • A guarantee of intent or knowledge.
  • A substitute for chain-of-custody and documentation.

If you keep one mental model, keep this: hashes are identifiers of data, and the legal question is how that identifier was generated, matched, and described.

For a more comprehensive introduction to digital hashing for lawyers, including its role in digital forensics and chain of custody, see Digital Hashing for Lawyers: Understanding the Essentials for Criminal Defense.

What “known hash” matching is

Investigators often use “known-file” databases. These databases store hash values for files that have been previously classified. When a new investigation sees a hash match, the system can infer that the file is the same as a previously known file.

Project VIC is one example of a community-driven program designed around classifying and sharing identifiers for known files [2].

This is where the phrase known hash probable cause shows up. The logic is:

  1. A particular hash value is associated with a known file in a trusted reference set.
  2. The investigation observed that same hash value in the current case context.
  3. Therefore, the affidavit argues there is probable cause to believe the target file is the known file.

That can be persuasive. It can also be overstated if the affidavit is sloppy about which hash was observed and what was actually matched.

The critical distinction: torrent infohash vs file hash

This is one of the most common technical translation problems I see.

  • A file hash is computed over a file’s bytes (the actual file content).
  • A torrent infohash (often shortened to infohash) is computed over the torrent’s “info” dictionary (metadata describing the content) and is used as an identifier in the BitTorrent protocol [3]. (For more on BitTorrent basics, see BitTorrent CSAM Investigation Explained.)

These are not interchangeable.

Why this matters

If an affidavit says “the hash value matched a known file,” the defense should ask:

  • Was the hash a file hash (content identifier), or an infohash (torrent identifier)?
  • If it was an infohash, how was the leap made from torrent metadata to a known-file classification?
  • Was there a controlled download and independent file-hash verification, or was the inference based on identifiers alone?

This is the practical difference between “BitTorrent infohash evidence” and true file-content verification.

How hash claims show up in Torrential Downpour cases

In BitTorrent-focused investigations, the tool output frequently records:

  • The torrent identifier (often the infohash).
  • The target peer (IP address and port).
  • The investigative steps used to connect, exchange protocol messages, and in some cases download data.

When you see the phrase Torrential Downpour hash value probable cause, the affidavit is usually trying to bridge a protocol identifier to a content classification. That bridge can be solid, but you must verify the supports.

Defense angles (what to verify, line by line)

Here is an affidavit review workflow that tends to pay off.

1) Identify exactly which hash type is referenced

Look for:

  • “infohash,” “torrent hash,” “hash of the torrent,” or “info_hash” in logs.
  • “MD5,” “SHA-1,” “SHA-256,” or “file hash” in forensic reports.

If the affidavit uses the generic word “hash” without specifying which one, that is a red flag. At a minimum, it creates room for clarification and sometimes material overstatement.

2) Validate the matching process

Ask:

  • What database was used for “known file” matching?
  • What is the provenance of the reference set?
  • What record shows the match (screenshot, export, log entry, report)?

This is where “hash match probable cause” can collapse into “someone said it matched.” You want a record.

3) Check for overstatements

Common overstatements include:

  • Treating an infohash as if it were a file hash.
  • Treating “participated in the torrent” as “possessed the complete file.”
  • Treating an identifier match as proof of user intent.

Courts have addressed warrants and probable cause questions in cases where hash evidence and investigative descriptions were central. For example, United States v. Miknevich discusses probable cause issues in the context of file identification language and investigative facts [4]. Likewise, United States v. Crist includes discussion of investigative methods and warrant issues in a case involving illegal file investigations [5].

Do not assume these cases map perfectly to your facts. Use them as a reminder: courts often care about whether the affidavit’s language accurately matches what the investigation actually did.

4) Confirm whether “visual confirmation” occurred

Some affidavits include language like “the investigator confirmed the content.” Others rely on hash-set identification alone.

Either approach can be litigated. The key is accuracy and documentation.

If an affidavit implies visual confirmation, ask:

  • Who performed it?
  • When?
  • On what system?
  • What record exists of that confirmation?

If the affidavit did not involve visual confirmation, your focus shifts to the reliability of the hash match and the integrity of the logging.

Collision concerns vs operational errors

Collisions (usually a low-probability issue)

In theory, two different inputs can produce the same hash output (a collision). For strong cryptographic hashes, this is designed to be extremely difficult, and the practical risk in a well-documented workflow is generally low [1].

In litigation, collision arguments rarely win on their own unless you have case-specific facts that make the match suspect.

Operational errors (where real problems occur)

Operational and human errors are far more common:

  • Mislabeling a hash type in an affidavit.
  • Copy/paste errors across cases.
  • Time zone confusion.
  • Mixing up target IP/port pairs across sessions.
  • Overstating what a tool output shows.

If you are looking for a practical place to invest time, invest here. Operational errors are testable. They also map to discovery requests and cross-exam questions.

Practical checklist: what to request in discovery

If your defense strategy depends on challenging or validating the hash narrative, request artifacts that let you test it.

  • Hash evidence
    • The exact hash value(s) referenced.
    • The algorithm used (MD5, SHA-1, SHA-256, etc.).
    • The record of the match (export/log/screenshot).
  • Identifier context
    • If an infohash was used, the torrent metadata that produced it.
    • Any mapping records between the infohash and a known-file classification.
  • Tool output
  • Timekeeping and attribution
    • Time zone and clock sync method.
    • ISP subpoena return and timestamp handling.

If you need help translating the technical records into a targeted discovery letter, contact Lucid Truth Technologies using the LTT contact form: Contact.

Conclusion

Hash matching is a powerful investigative tool. It can also be misunderstood. In Torrential Downpour cases, the most important defense move is often simple: confirm what hash was actually observed, confirm what it was matched against, and confirm that the affidavit’s language is faithful to those facts.

That approach keeps the conversation anchored to testable evidence and avoids hand-waving.

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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] National Institute of Standards and Technology, “Secure Hash Standard (SHS) (FIPS 180-4),” NIST, 2015. [Online]. Available: https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.180-4.pdf

[2] Project VIC International, “Project VIC International,” Project VIC, 2025. [Online]. Available: https://www.projectvic.org/

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

[4] United States v. Miknevich, No. 10-1546 (3d Cir. 2011), CourtListener. [Online]. Available: https://www.courtlistener.com/opinion/205734/united-states-v-miknevich/

[5] United States v. Crist, 627 F. Supp. 2d 575 (M.D. Pa. 2008), CourtListener. [Online]. Available: https://www.courtlistener.com/opinion/1974111/united-states-v-crist/