MONDAY, MAR30
1. Payjoin wallet fingerprints, 2. Binance iran compliance, 3. Bhutan bitcoin drawdown, 4. Fannie Mae bitcoin mortgages
From Proto and Bitkey - part of the Bitcoin ecosystem at Block, Inc.
1. fingerprint
Armin Sabouri at the Payjoin Foundation has published a technical analysis showing that wallet-level fingerprints can systematically undo the privacy guarantees Payjoin transactions are designed to provide. Payjoin works by merging sender and receiver inputs into a single transaction, defeating the Common Input Ownership Heuristic that chain analysis relies on. But when the two parties use different wallet software, those tools leave distinguishable traces: Bitcoin Core grinds ECDSA signatures to low-R values while most wallets do not, Taproot spending policies differ in whether they include an explicit SIGHASH_ALL byte, and nSequence values vary predictably per implementation. Sabouri walks through three real Payjoin transactions involving Samourai, the Payjoin Dev Kit, Cake Wallet, and Bull Bitcoin Mobile, showing how a single signature length mismatch can partition inputs by owner and reconstruct the payment amount. The analysis confirms that fingerprint homogeneity between sender and receiver is a necessary condition for Payjoin privacy, and that inter-transaction graph analysis can resolve ambiguities that appear unresolvable in isolation. The Payjoin Foundation says it is building automated tooling to measure fingerprint leakage at scale as part of its privacy metrics framework.
-EDITOR·OP_DAILY2. surveillance
David Yaffe-Bellany and Michael Forsythe at the New York Times report that the clues pointing to sanctions evasion at Binance were sitting in public records for over a year before anyone acted on them. In November 2024, the U.S. Commerce Department placed an entire Hong Kong address on its export restriction list after finding six firms there at risk of violating Iran sanctions. One of those firms shared a Singapore villa address with the chief executive of Blessed Trust, a Binance vendor that ultimately moved $1.2 billion through the exchange to Iran-linked wallets. A related account belonging to a 78-year-old business partner transferred $439 million to intermediaries connected to the IRGC and the Houthis between January and March 2025. Binance’s own internal systems had flagged Blessed Trust accounts with the notation “Don’t block. Internal accounts,” and a Telegram message described Blessed Trust’s representative as a “friend of Rock,” referring to a Binance board member. When compliance investigators surfaced the findings, four were suspended or fired. The Justice Department is now investigating the transfers. Binance has pleaded guilty to sanctions violations once before, paying $4.3 billion in 2023, and founder Changpeng Zhao received a presidential pardon from Trump last October.
-EDITOR·OP_DAILY3. drawdown
Blockchain analytics platform Arkham Intelligence flagged a 519.7 BTC transfer worth approximately $36.75 million from the Royal Government of Bhutan to Singapore-based OTC desk QCP Capital, the latest in an accelerating liquidation campaign that has now reduced the Himalayan kingdom’s reserves by roughly 66% from their late 2024 peak of 13,000 BTC. Year-to-date outflows from the sovereign treasury operated by Druk Holding and Investments have exceeded $120 million, with March transactions running significantly larger than the $5 to $15 million clips typical of January and February. Bhutan built its entire stack through government-operated hydroelectric mining at near-zero production cost, meaning every sale represents essentially 100% realized profit. Analysts suggest proceeds are being directed toward Gelephu Mindfulness City, a major planned special economic zone in the south of the country, though the government has issued no official statements on the sales. Despite the drawdown, Bhutan retains roughly 4,453 BTC valued at around $315 million and remains the world’s seventh-largest sovereign bitcoin holder. The post-halving compression of mining margins and rising domestic energy demand appear to have changed the economics of continued accumulation.
-EDITOR·OP_DAILY4. mortgage
Reporting in Bitcoin Magazine, Micah Zimmerman covers a structural shift in U.S. housing finance: Coinbase is partnering with Better Home and Finance to offer bitcoin-backed mortgages that conform to Fannie Mae standards, the first time the government-sponsored enterprise has accepted digital assets as collateral. Qualified borrowers can pledge bitcoin or USDC as a down payment without liquidating their holdings, sidestepping potential capital gains events while maintaining asset exposure. The loans carry no margin calls and no collateral top-ups if bitcoin’s price falls, with liquidation risk limited to borrowers at least 60 days delinquent. Better CEO Vishal Garg estimated the firm may have missed up to $40 billion in originations by not offering this product sooner. Interest rates are expected to run 0.5 to 1.5 percentage points above standard 30-year rates. Coinbase data shows 45% of younger investors hold bitcoin compared to 18% of older cohorts, suggesting the product targets a generation for whom digital assets have become the primary savings vehicle. The companies say roughly 52 million Americans have held digital assets at some point.
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