SHRINCS: 324-byte stateful post-quantum signatures with static backups

The concept introduced by Jonas Nick regarding the use of stateful signing in SHRINCS highlights a significant innovation in cryptographic key management. The primary challenge addressed is ensuring that the stateful keys have never been used before, which is critical for security. To overcome this, it is suggested that rather than generating a new master seed, the signer software could derive a pseudorandom child key using a self-generated salt or "ID." This approach maintains the integrity of the "virgin state" by ensuring that the salt has sufficient entropy to avoid collisions, thus making it highly unlikely for the keys to be duplicated.

Furthermore, the derived keys from this method are unlinkable without access to the master seed itself, thus preserving privacy without compromising on security. This methodology marks a substantial improvement over previous schemes, where there was a need to rotate seed phrases to reuse the stateful path safely. Now, with the proposed change, backing up the IDs suffices, and since these are safe to share publicly, they can be stored virtually anywhere—be it on-chain, through Nostr, IPFS, Dropbox, or a git repository. This flexibility in storage ensures that they can be accessed whenever needed for restoration by the user or wallet software.

Another noteworthy aspect of deploying SHRINCS in real-world applications is that each ID can represent an individual HD wallet. This allows for the derivation of potentially unlimited SHRINCS keypairs under a single ID, which can then be utilized for various wallet addresses. This feature adds a layer of versatility and scalability to the use of SHRINCS in managing wallet addresses and enhances the practical utility of stateful cryptographic keys in broader applications.