I wrote the python code for this.  It was a little trickier to get it right:

https://gist.github.com/earonesty/ea086aa995be1a860af093f93bd45bf2

Spender publishes an ephemeral anchor tx committing to a future secret
without revealing the secret in one block.

Spender publishes the revealed secret and spend in a future block.

New opcode needs to verify that the anchor tx was published at least N
blocks prior to the spend block.

This creates the necessary information asymmetry without being a true
signature, relying on asymmetry-over-time to protect against quantum
threats.



On Wed, Dec 17, 2025 at 12:57 PM Erik Aronesty <erik@q32.com> wrote:

> Was thinking about this and I realized that a quantum-resistance scheme
> doesn't technically need a new "signature" - because those constraints
> (generality) are far harder than needed for Bitcoin's "proof of utxo
> ownership".
>
> Instead of new signatures, I propose a chain-native authorization
> primitive whose security is bounded by the same economic assumptions as
> transaction finality itself. The objective is a quantum migration path that
> can be deployed immediately, does not require large witnesses, remains
> cheap to validate, and does not rely on assumptions stronger than those
> already required to trust confirmed spends.
>
> The construction relies on a minimal new introspection primitive rather
> than a wholesale redesign of Script. A single opcode exposes a
> chain-derived challenge tied to the spent output, defined as the block hash
> at a selectable offset from the block in which the UTXO was created. The
> offset is fixed by the locking script and can be chosen to reflect the
> value at risk. Larger offsets correspond to deeper confirmation depth and
> higher economic resistance to manipulation (an enforced confirmation wait).
> Existing timelock opcodes already enforce the required delay; the only
> missing element is access to this chain-defined value.
>
> *This is commit–challenge–response (Σ-protocol–derived) authentication*,
> but the challenge is provided by *the future chain*.   This is a well
> known scheme.
>
> Authorization is conjunctive, not alternative. A valid spend must satisfy
> both a traditional signature check and a delayed, chain-conditioned
> hash-based proof. The traditional signature preserves today’s security
> assumptions and compatibility, while the chain-conditioned proof adds a
> quantum-resistant requirement that cannot be bypassed by a quantum
> adversary. Either condition alone is insufficient. This ensures the scheme
> is strictly at least as secure as current authorization and strictly
> stronger against quantum-capable attackers.
>
> The delayed component commits to randomness in advance and later reveals
> it combined with a hash of the chain-provided challenge. Verification
> consists only of checking the timelock, evaluating a hash operation, and
> verifying the traditional signature. There is no large witness, no
> algebraic structure, and no expensive validation path. Failure requires the
> ability to bias or reorganize the chain across the selected confirmation
> window, which is the *same failure mode already implicit in transaction
> finality*.
>
> This design enables quantum migration without changing address formats,
> inflating transaction sizes, or introducing fragile cryptographic
> assumptions. It aligns authorization with the economic security model the
> system already relies on and provides an enforceable, compact, and
> conservative quantum-resistance mechanism that can be adopted incrementally.
>
> If anyone is interested in a BIP or further development of this security
> construct, please let me know.
>
> - Erik
>

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