Bitcoin’s Alert Key Published by Bitcoin Developers
The Bitcoin Alert Key, which has been used on some rare emergency situations, has been published by the Bitcoin developers and revealed by Brian Bishop. He revealed the codes for the mainnet, the mainnet private key, the testnet public key and the testnet private key.
The original alert key functionality was removed from the Bitcoin protocol in 2016 pre-segwit and it remained non-public in the updates until today. Up until that point, a small number of individuals had access to the key and any of them could send or cancel alerts that had been sent to the network.
Generally, the alert keys were used when the nodes had to be verified quickly. One occasion was in 2013 when an unintentional fork happened. The members of the community state that the keys were never misused when they were still a part of the Bitcoin code. Its removal was justified via the basis that they could be misused, though.
The alerts were generally non-intrusive and worked as a method of notifying the node operators quickly for important and possibly dangerous developments. Right now, there is no way to make direct notifications anymore, as the revealed codes are no longer operational because they have been removed from the protocol.