Adam Back Warns MPC Custody Is Too Complex as Blockstream Pushes Offline Bitcoin Storage

Blockstream co-founder and CEO Adam Back says conventional multi-party computation (MPC) protocols are too interactive and too complicated to secure for fully offline Bitcoin custody, positioning his company's newly launched Bitcoin custody system around air-gapped signing instead. Back, whose pre-Bitcoin Hashcash invention helped lay the groundwork for proof-of-work, made the remarks to Cointelegraph.

"When people talk about MPC, they're talking about some very esoteric and complicated protocols that are hard to secure and are very interactive. So you can't really use them in a cold storage setting," Back said.

What does Back argue went wrong at Binance?

Back pointed to the $6.3 billion Binance hack as the clearest evidence of the risks built into internet-connected custody infrastructure. According to Binance's own investigation, attackers compromised employee devices and obtained credentials that opened the exchange's wallet-signing infrastructure.

His reading of the incident is structural rather than incidental. If signing equipment touches the internet at all, defenses such as firewalls do not remove the exposure. "You can get hackers into the network, get hackers with access to logins they shouldn't have and so on," he said. In other words, the breach was not a failure of one control but a consequence of the architecture itself: a signing device that is reachable is a signing device that can be reached by the wrong party.

The operational consequence for custodians is straightforward. Keeping signing devices offline, Back argues, prevents the class of unauthorized access that credential theft enables. That is the design premise behind Blockstream's new custody system, which treats disconnection from the network as the primary control rather than a supplementary one.

Why does AI change the calculus?

Back also flagged a second, forward-looking pressure on custody security: artificial intelligence. He said AI tools could help attackers discover subtle flaws in complex MPC implementations that a human auditor might miss.

"The AIs can help attackers find small implementation errors and things like that, which may not be obvious," Back said.

The concern is not hypothetical for complex protocols. The more intricate a cryptographic implementation, the more surface area exists for small defects — and machine assistance lowers the cost of finding them. Back's conclusion follows directly: complexity itself has become a liability, and simpler systems age better against automated attack tooling.

The caveat deserves stating plainly. AI-assisted vulnerability discovery is a plausible risk, but no incident of that kind is documented in the source material. The claim is an argument, not an observed event.

Will the custody industry follow?

Asked whether the broader custody sector would adopt similar offline models, Back said he hoped so, arguing institutions should "adapt to the environment" by moving assets into cold storage to reduce exposure to potential AI-assisted attacks.

"Complexity is the enemy of security. And going back to basics is the answer, you know, just cold-store it," Back added.

That recommendation carries trade-offs the source does not address. Offline custody reduces attack surface, but it also slows withdrawal and settlement workflows, which matters for exchanges and institutions that must move client assets quickly. Whether the industry accepts that friction in exchange for resilience remains an open question, and Back's hope is not evidence of adoption.

The takeaway is simple: one of Bitcoin's foundational cryptographers is betting that the future of institutional custody looks less like elaborate distributed protocols and more like devices that never connect at all.