# The third-party doctrine

> The third-party doctrine (US federal courts): Why chain analysis needs no warrant. Region: Americas. Restricts anonymity: Anonymity-enhancing assets or unattributed transfers are barred outright, or barred for regulated firms.

Part of the Soda Labs Privacy Hub regulation map, which reads the instruments
themselves rather than summarising the summaries: https://www.sodalabs.xyz/privacy-hub/regulation

## Key facts

- Entry type: Regulator or standard-setter
- Region: Americas
- Subject: Why chain analysis needs no warrant
- Authority: US federal courts
- Stance on on-chain confidentiality: Restricts anonymity. Anonymity-enhancing assets or unattributed transfers are barred outright, or barred for regulated firms.
- Tags: Fourth Amendment, Gratkowski, chain analysis, subpoena
- Canonical page: https://www.sodalabs.xyz/privacy-hub/regulation/reg-third-party-doctrine

## What it actually says

Any account of US financial privacy that stops at statutes misses the layer that actually decides things. Because records handed to a third party carry no constitutional protection, chain analysis combined with a subpoena to the exchange is a lawful warrantless route from an address to a name. The Fifth Circuit blessed exactly that sequence in 2020, noting that agents used a commercial clustering vendor and then served a grand jury subpoena on Coinbase rather than seeking a warrant. The First Circuit followed in 2024, and the Supreme Court declined to hear the appeal in June 2025. The 2018 cell-site decision narrowed the doctrine for location data while leaving the financial records line untouched. This floor has not moved.

## The instruments that matter

- **United States v. Miller (1976) and Smith v. Maryland (1979)**: information voluntarily conveyed to a third party carries no reasonable expectation of privacy, the foundation for subpoenaing exchange records
- **United States v. Gratkowski (5th Cir., 30 June 2020)**: no reasonable expectation of privacy in Bitcoin blockchain records or in Coinbase account records; agents used clustering analysis plus a grand jury subpoena rather than a warrant
- **Carpenter v. United States (2018)**: narrowed the doctrine for historical cell-site location data as qualitatively different, while expressly preserving Miller
- **Harper v. Werfel (1st Cir., 24 September 2024)**: Coinbase account information falls squarely within the third-party doctrine; certiorari denied 30 June 2025

## Sources

- [United States v. Gratkowski](https://www.ca5.uscourts.gov/opinions/pub/19/19-50492-CR0.pdf)
- [Harper v. Werfel](https://www.ca1.uscourts.gov/sites/ca1/files/opnfiles/23-1565P-01A.pdf)

## Related entries

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- [NYDFS](https://www.sodalabs.xyz/privacy-hub/regulation/reg-nydfs): The most privacy-restrictive US regulator, state or federal
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- [US Treasury and the Working Group](https://www.sodalabs.xyz/privacy-hub/regulation/reg-us-treasury-pwg): The first federal endorsement of privacy technology