Three signers produced one on-chain signature
Bitcoin Cash developers Chris Pacia, Mark Lundeberg and the pseudonymous Checksum0 completed a three-party Schnorr-signed transaction on May 18, 2019, turning a recently activated protocol feature into a working on-chain demonstration.
The transaction, identified by hash `2b5fe26f6f903021b343da52d8d8b316c88986c480cfd6fc80ffbc027cbd2039`, spent funds controlled through an aggregate public key. The surviving developer transcript records three participants, their public-key exchange, three signing phases and the resulting single Schnorr transaction signature. A public block explorer independently preserves the confirmed transaction.
Bitcoin.com reported on May 19 that the transaction’s spendable output went to the Ross Ulbricht defense fund. That destination attribution comes from contemporaneous reporting and the decoded transaction, rather than from an independently audited account of the recipients.
The developers described the experiment as the first three-of-three Schnorr multisignature transaction. The chain record proves that this particular transaction occurred; it cannot, by itself, prove an exhaustive global priority claim. “First” should therefore be understood as the developers’ contemporaneous and widely reported characterization.
What the demonstration actually showed
Bitcoin Cash activated Schnorr signature verification on May 15, 2019. The upgrade permitted Schnorr signatures with `OP_CHECKSIG` and `OP_CHECKDATASIG`, but it did not yet add Schnorr support to the protocol’s traditional `OP_CHECKMULTISIG` operation.
The May 18 demonstration worked differently. The three participants combined their public keys into one aggregate public key and cooperatively generated one valid signature. To the consensus rules, the resulting spend could be checked through the ordinary single-signature path. The transaction therefore demonstrated multisignature behavior through cryptographic aggregation, not a conventional script listing three keys and requiring three separately verified signatures.
That distinction mattered. Conventional multisignature scripts exposed their structure on-chain and required more signature and key data. Aggregation offered a path toward smaller, less revealing transactions whose cooperative origin was not necessarily apparent from the locking script alone. Those benefits remained prospective for production wallets: Lundeberg’s demonstration software explicitly warned that it was experimental and could lose funds.
A live-network test, not a finished wallet feature
The event was consequential because it moved Schnorr aggregation from specifications and test code onto a publicly verifiable network. It showed that independently controlled keys could participate in an interactive signing process and produce a signature accepted by the upgraded Bitcoin Cash rules.
Market context also made the experiment more than an isolated laboratory test. CoinMarketCap’s May 18 historical snapshot ranked BCH fourth among listed cryptoassets at $357.62, with a market capitalization of $6.36 billion after rounding its reported $6,361,880,486.79 figure. Those are provider-aggregated snapshot values, not an executable quote from one exchange, and they do not establish that the demonstration moved BCH’s price.
The transcript also revealed practical limitations. Participants exchanged commitments, nonce-related points and partial signing values across multiple phases. Wallets would need reliable coordination, secure nonce handling and safeguards against malicious participants before the method could support routine custody arrangements. The demonstration established feasibility, not operational readiness or a security audit.
Later protocol context
Bitcoin Cash added separate Schnorr support to `OP_CHECKMULTISIG` in its November 15, 2019 upgrade. That later change should not be projected backward: the May 18 transaction used aggregate-key signing with `OP_CHECKSIG`. Its event-day significance was narrower but still concrete—a newly activated signature scheme had supported a cooperative, confirmed spend on the live network.
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