Posted by [By Kyana Givens]
A blockchain is a digital ledger, a continuously growing list of records called “blocks” that are linked together and secured using cryptography. Each block contains transaction data, a timestamp, and a coded reference to the block before it. That structure makes the data extremely difficult to alter, because changing one block invalidates everything after it.
Blockchains are decentralized, meaning no single authority controls them. Public blockchains like Bitcoin are transparent: anyone can see the transactions. Users are identified by coded addresses rather than real names, but their transactions can still be traced.
Here is how this plays out in a criminal case. Say federal agents suspect the accused of running an online drug marketplace that accepts Bitcoin. They get a court order requiring a cryptocurrency exchange to produce records linking the accused’s account to a specific wallet. Using blockchain analysis software, agents then trace money moving across multiple wallets, connecting the accused to thousands of illegal transactions.
After indictment, the accused moves to suppress the evidence, arguing that law enforcement reviewed the public blockchain without a warrant in violation of the Fourth Amendment. The government counters that because blockchain records are publicly visible, similar to information voluntarily shared with companies like Google, no warrant was required under the third-party doctrine.
These cases raise questions courts are still working through: What privacy expectations do people have in blockchain data? Does the third-party doctrine hold in the digital age? And what level of judicial authorization is required before the government can force an exchange to connect a wallet to a real person?
I have penned a memorandum that explores what the Eleventh Circuit’s take on blockchain evidence means for your suppression motion―and why the shadow of Carpenter v. United States, 585 U.S. 296 (2018), still reaches this fight. You’ll find the memo at this link. As always, if you’d like to chat about your own case, please reach out to me or to anyone at the Federal Defender Program.
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