DEF Submits Amicus Brief to Protect American's Fourth Amendment Rights

On March 28, 2025, DEF submitted an amicus brief in support of Jim Harper’s petition for certiorari to the United States Supreme Court in Harper v. Werfel. Harper’s case relates to the IRS’s warrantless acquisition of digital asset transaction records from Coinbase through a “John Doe” summons, raising critical questions about whether individuals retain their Fourth Amendment right to privacy in financial data shared with third-party platforms. 

The case challenges the continued expansion of the “third-party doctrine” – a legal principle  that says if you voluntarily share information with a third party, you lose your Fourth Amendment protection over that information – in the digital age. And, the case asks the Court to clarify whether the Constitution protects individuals against mass government surveillance of financial activity on public blockchains past, present, and future, once a user’s identity has been linked to a particular wallet address.

We spoke to DEF’s legal intern, Spencer Peek, to learn about why this potentially precedent-setting case matters, and to dig into the highlights of DEF’s latest Amicus brief: 

1. Spencer, thanks for chatting with us. What is DeFi Education Fund arguing in our latest Amicus Brief? 

In our brief, we urge the Court to grant certiorari — affirming the constitutional principle that privacy protections must evolve with modern technology, as recognized in Carpenter v. United States. DEF argues that the IRS’s warrantless acquisition of digital asset transaction records from Coinbase violates the Fourth Amendment protection against unreasonable search and seizure. 

We take the position that information collections of this sort improperly enables mass surveillance of financial records without individualized suspicion or judicial oversight. We believe the “third-party doctrine,” rooted in cases like Smith v. Maryland and United States v. Miller, should not apply to blockchain-based records that, once linked to a user’s identity, allow the government to retroactively and prospectively monitor a person’s entire financial life. 

2. Can you please give us a brief overview about the core issue presented in Harper v. Werfel (IRS)? 

First, it’s important to note that the case name is formally Harper v. Werfel – but is colloquially referred to as Harper v. IRS. Daniel Werfel was the Commissioner of the IRS from 2023-2025, and for the purposes of our conversation, I’ll use Harper v. Werfel, for accuracy. 

The core issue is whether the IRS violated Harper's right to privacy guaranteed by the Fourth Amendment – when it compelled Coinbase to turn over extensive transaction data, spanning three years and involving over 14,000 users, without a warrant or individualized suspicion. The petitioner, Harper, and DEF as amici, argue that the IRS’s data collection constitutes a search under Carpenter v. United States because it enables pervasive surveillance.

3. Can you quickly recap the history of the Harper v. Werfel case? 

The case was originally brought by Jim Harper, who filed a lawsuit in the District Court for the District of New Hampshire. Harper challenged an IRS "John Doe" summons issued to Coinbase, whereby the IRS requested records of thousands of Coinbase customers, including Harper. 

Ultimately, the district court rejected Harper’s argument, and then, on appeal, the First Circuit affirmed the district court’s dismissal of Harper’s claims. 

4. So, is this case about crypto, or is it bigger than crypto?

At the center of the case is a significant constitutional law question. When you share your information with a third-party, such as a bank, phone company, or digital asset exchange, like Coinbase, do you lose your Fourth Amendment protection against unreasonable search and seizure? 

This question has come to be governed by what is known as the “third-party doctrine.” The third-party doctrine has developed through Supreme Court cases beginning in 1976. 

The primary cases that created the third-party doctrine are Smith v. Maryland and United States v. Miller. They are often (in our view, improperly) cited to support the position that people have “no reasonable expectation of privacy” in information voluntarily shared with third parties. This, however, misstates the Court’s position in Smith and Miller. 

5. What, in your view, is the proper interpretation of the Court’s position in Smith and Miller? And, what exactly are these cases about?

Properly understood, the cases carved a narrow exception to Fourth Amendment protections – it is important to understand that this is not a sweeping rule. 

The cases Smith and Miller allowed the police to obtain a suspect's information without a warrant when that information was voluntarily conveyed to a third-party and the government engaged in a targeted collection of specific, limited types of information that involve particular individuals suspected of wrong-doing. Further, in both Smith and Miller, the Supreme Court emphasized that the third-party must also voluntarily convey the information to the government. But in Harper, Coinbase only turned the customer records over under the threat of contempt for non-compliance. 

The limits of the third-party doctrine were confirmed in 2018 in Carpenter vs. United States, where the Supreme Court made it clear that Smith and Miller “did not rely solely on the act of sharing” information with a third-party to eliminate Fourth Amendment protections. Instead, the Court held that Smith and Miller were confined to the acquisition of targeted, short-term, and non-invasive records, such as phone numbers dilated over a few days or basic backward looking bank records. 

In contrast, Carpenter held that accessing detailed, long-term historical cell-site location information, due to the depth, scope, and revealing nature of the information, constitutes a search subject to the Fourth Amendment.

6. If these past cases, especially Carpenter vs. United States, reaffirmed that third-party doctrine cannot be used for over-surveillance, why has this issue reemerged in Harper v. Werfel?

In Harper v. Werfel, the district court followed what we believe is a troubling trend of lower courts narrowly confining Carpenter to its facts, treating it as only applicable to historical cell-site location information. Despite Carpenter’s broad reasoning, some courts like the district court and First Circuit Court of Appeals in Harper have minimized its reach by refusing to apply its principles to other forms of deeply revealing third-party held data, such as cryptocurrency transaction reports.

Harper, and DEF as amici, argue that the Coinbase records at issue are much more similar to the cell site location information (CSLI) in Carpenter than the limited information sought in Smith and Miller. Why? Because the Coinbase records allow the government to construct a detailed, long-term chronicle or a person’s financial activity. 

They reveal sensitive insights into the user’s private life, and critically, the inclusion of crypto wallet addresses and public keys allows for ongoing, forward-looking surveillance. Said differently, once a user’s identity is linked to a crypto wallet address, the government has the ability to track all future transactions indefinitely, because the transactions are taking place on technology that is available transparently for public viewing: a public blockchain.

7. Has the Supreme Court already agreed to hear this case?

No, the Supreme Court has not agreed to hear Harper v. Werfel yet. Harper recently filed a Petition for Certiorari, which means the petitioner has asked the Supreme Court to review the lower court’s decision.

The Supreme Court has not yet granted that request. For certiorari to be granted, at least four justices must agree to hear the case. 

8. What happens if the Supreme Court does not agree to hear the case?

If the Supreme Court denies certiorari, that means it has declined to hear the case, and the decision of the First Circuit Court of Appeals will stand as final. 

9. How could the outcome of this case impact the future of DeFi in the United States?

This case may establish precedent for how the Fourth Amendment applies to modern digital financial records, particularly relating to digital asset records held by third-party platforms. Unlike traditional financial records, blockchain transactions are recorded on a public, immutable ledger, meaning that once a user’s identity is linked to a blockchain address, the government can trace a complete history of past transactions and monitor all future activity in real-time – without obtaining a warrant. 

If the lower court’s ruling were to stand, it could stifle innovation, discourage user adoption of blockchain innovations, and continue to allow for broad, warrantless surveillance of financial activity on blockchains. 

10. What are the immediate next steps in Harper v. Werfel?

After a petition for certiorari is filed, the immediate next steps are for the respondent (in this case, the government) to file a response, after which the Supreme Court will circulate the petition for review among the justices. The Court will then decide whether to grant or deny certiorari, a decision that requires agreement of at least four justices. 

Spencer, thanks so much for making the time to chat with us. 

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