Giving teeth to expected EC disabling: P2XX(-T)(-ML)

A recent proposal suggests a new method for enhancing security against post-quantum threats in Bitcoin transactions by introducing a tripwire mechanism. This approach involves utilizing a 128-byte value, denoted as "aRsm", where 'P' represents a public key computed as N+a*G. Here, 'N' is defined as the BIP-341 NUMS point, and 'Rs' signifies a BIP340 signature of message 'm' by 'P'. This setup aims to enable triggering of the tripwire not only by victims of key-path spending but also by those with direct access to a CRQC.

The proposal advocates for integrating the tripwire directly into blocks through the coinbase witness commitment output rather than associating it with specific transactions. This would simplify the verification process as nodes would only need to inspect the coinbase for any signs of the tripwire. To facilitate this, a new P2P message would be necessary to convey the proof required to break the elliptic curve discrete logarithm (ECDL), which miners would need to relay. Implementation might demand updates to stratumv2 or getblocktemplate to ensure that mining pools can incorporate this information into the coinbase effectively.

To mitigate potential risks associated with this change, several safety measures have been proposed. These include requiring a unanimous signalling threshold for activation, extending the signalling period to 4032 blocks, and employing a phased activation strategy. The strategy suggests a continual soft-forking technique where 100% signalling both activates the mechanism and adapts its validation timeline progressively from 2026 to 2027, adjusting the legitimacy of signals based on specified dates to ensure readiness and compatibility of the network.

These proposed changes aim to bolster Bitcoin's resilience against emerging quantum computing capabilities while maintaining network integrity and backward compatibility through careful phasing and stringent consensus requirements.