- Arkham claimed to have identified individuals behind more than half of ZCash transactions, including shielded transactions.
- Shielded “z-address” transactions, designed to provide privacy, remain undisclosed according to experts and the Zcash community.
- Arkham later clarified that shielded-to-shielded (z-to-z) transactions were not labeled in their analysis.
- The claim sparked widespread pushback and fact-checking on X, with multiple Community Notes disputing the breakthrough.
- Zcash users and its founder publicly challenged Arkham to prove the ability to deanonymize shielded transactions.
In December 2025, blockchain analytics firm Arkham posted on X that it had deanonymized some of Zcash’s shielded transactions, which are meant to be private. The post claimed that more than half of all Zcash transactions—both shielded and unshielded—were labeled with the responsible individuals and institutions identified.
Zcash shielded transactions, using z-addresses, are intended to keep transaction details private, forming about one-fifth of total Zcash transactions. However, Arkham‘s claim did not specify how many shielded transactions were included versus unshielded, transparent transactions, also known as t-transactions.
The post garnered significant attention, amassing over 500,000 impressions. It quickly received multiple fact-checks through X’s Community Notes system, which disputed the claim. One contributor wrote, “Z-Z transactions have not been deanonymized. Arkham only provides data for the remaining ~80% of transparent transactions.” Another note added, “Arkham did nothing groundbreaking here despite the clickbait title.” A Zcash community member also clarified on Twitter that “They haven’t tracked Zcash’s private transactions: searching for Z addresses returns no information.”
Critics pointed out that including shielded and unshielded transactions together created confusion. Legally, 0% of shielded and 100% of unshielded transactions could sum to more than half, so claiming to have deanonymized both groups without separation was misleading. Arkham referenced an old example—the seizure of Zcash linked to the AlphaBay founder in 2017—to bolster their transparency claim.
The Zcash community reacted swiftly, with some users challenging Arkham to deanonymize their shielded addresses. One asked for clear confirmation whether Arkham could track shielded-to-shielded transactions specifically.
After about 18 hours, Arkham posted a follow-up acknowledging that “z->z transactions are not accounted for in the 50% of Zcash transactions labeled.” Despite the correction, the firm did not retract the initial claim. The founder of Zcash, Zooko Wilcox-O’Hearn, publicly urged Arkham to clarify their statements.
Zcash’s privacy model operates on default unshielded transactions, meaning most users do not automatically use shielded addresses unless they opt in. This makes transparent transactions easier to analyze. The discussion highlighted that Arkham effectively tracked these transparent transactions but did not break the privacy provided by shielded z-addresses.
For additional details, see Arkham’s original post and community responses on X.
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