How The War For Bitcoin P2SH Was Fought – Bitcoin Magazine

“Push the date back two months. OP_EVAL just is not ready yet.”

It was the verdict Gavin Andresen had worked so long to avoid. With a single rebuke sent from Russell O’Connor’s keyboard, a months-long effort to upgrade Bitcoin — the first in the wake of founder Satoshi Nakamoto’s exit — was abruptly stalled ahead of implementation.

As revealed by O’Connor, the proposed command — heralded by Andresen as the “fastest path” to more secure Bitcoin wallets — could be exploited to create transactions that would send the software into an infinite computational loop in an attempt to validate them.

In short, OP_EVAL could be abused to crash Bitcoin nodes, and thus the Bitcoin network.

“It took me all of 70 minutes of looking to find this bug,” O’Connor wrote, condemning a process that had merged — and nearly pushed — bad code into the live software. “You guys need to stop what you are doing and really understand Bitcoin.”

It was the first serious setback for Andresen, the project’s new lead, who was quick to protest. In his view, abandoning OP_EVAL wouldn’t just waste months of coding and review, it would leave users without tools to protect against the trojans and viruses then plundering their digital wallets.

This was at the heart of OP_EVAL’s appeal — easy multisignature wallets would allow users to recover bitcoin, even when backups were lost; services might be built to send bank-like alerts, deterring fraud and theft; and better still, this could all be achieved in transactions that would look and behave like those users knew and understood.

But O’Connor’s words of warning were enough for those who had seen their concerns about the escalating pace of development validated.

“I would like to remind everyone that we are messing with a $20+ million dollar thing,” developer Alan Reiner would write. “There’s more than just a piece of software at stake —…

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