What was the Bitcoin Alert Key?

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  • The Bitcoin alert key was implemented in Bitcoin’s software in 2010
  • The key was implemented after the value overflow bug in 2010
  • What was the alert key and what was its purpose?

The Bitcoin alert key is being misconstrued by supporters of the BSV blockchain as a rationale for the coin recovery tool that it launched last month. Its supporters claim that by implementing a tool that can freeze and reassign BSV coins, the blockchain is re-implementing a tool that was already present in Bitcoin but that was removed. However, the reality behind the implementation of the alert key in Bitcoin’s early days is very different.

The Value Overflow Bug

The Bitcoin alert key was hastily implemented by Satoshi Nakamoto on August 15, 2010. This was in the wake of the ‘value overflow incident’, where someone was able to exploit some code that was used for checking Bitcoin transactions. This resulted in 184 billion extra bitcoin being created, which, obviously would have broken the protocol had it not been spotted and fixed.

Satoshi implemented a fix within three hours via a hard fork (Bitcoin’s first), and later implemented the alert key system, whose purpose he explained in a blog post on Bitcointalk:

In cases like the overflow bug or a fork where users may not be able to trust received payments, the alert should keep old versions mostly safe until they upgrade. Someday when we haven’t found any new bugs for a long time and it has been thoroughly security reviewed without finding anything, this can be scaled back. I’m not arguing that this is the permanent way of things forever. It’s still beta software.

Alert Key Was Not a Coin Freezing Tool

So the alert key was a short-term additional layer of defense against hackers, with node operators and miners informed via an alert that the software had been compromised and to take action. It was never, as much as the BSV contingent like to claim, intended to be used to freeze anyone’s coins with a court order.

How do we know this? We can surmise it because it was never, ever discussed, or even suggested as a possible knock on effect, by any of the parties talking about its implementation in 2010 or its removal in 2016. If there was any possibility that arbitrate confiscation of coins was a ramification of the alert key, someone would have mentioned it.


The alert key lay dormant until it was activated in February 2012, a false positive triggered by a protocol change. In 2016, the alert system was retired because of the possibility of privileged users sending political alert messages, and because of the possibility that the alert key was taken from Mt. Gox CEO Mark Karpelès by the Japanese police after his arrest in 2014.

As we know, this was in line with Satoshi’s wishes, with the alert key only supposed to be in place until Bitcoin was sufficiently bug-free, completely opposed to the idea of Craig Wright collecting thousands of BSV coins he says were stolen in a highly improbable hack in 2020.