R+15 Long-Horizon Evidence

01 What R+15 proves

Still checkable after the next algorithm change, and the one after.

R-Series receipts are designed to carry two signatures, Ed25519 and ML-DSA-65. That protects them against a quantum computer as far as anyone can currently foresee. But a land registry, a clinical trial or an AI decision audit may need to be checked in twenty years, by people who will be using algorithms that do not exist yet.

R+15 proves that evidence stays verifiable across algorithm generations and decades. It does so without re-signing history: originals are never changed. Instead, newer suites seal over older ones, and the chain of seals can be checked end to end.

The same layer also carries a second promise for autonomous systems: a decision made while a link was down can still be checked later.

Never re-sign history. Seal it, and seal the seal later.

02 Watch an archive age

From today to twenty years on.

Renewal ladder01 / 05

01 · SEAL

The archive is sealed in segments.

Receipts are chained as usual. At intervals, an archive manifest covers a segment. The manifest is signed with a hash-based signature (FIPS 205), whose security rests only on hash functions, and carries two different hashes.

02 · WITNESS

An independent witness cosigns the checkpoints.

Checkpoints of the log are published in a standard format. They are designed to be cosigned by an independent witness, so a forked or rolled-back history would be visible to anyone comparing notes.

03 · RENEW · NEXT SUITE

A newer suite seals over the older one.

When the archive suite needs strengthening, a renewal receipt covers the existing range under a new suite. The originals are untouched; the renewal vouches that they existed, unchanged, while the old suite was still trustworthy.

04 · RENEW · LATER SUITE

The ladder climbs again.

Each renewal covers everything below it. The rungs form a ladder from the original suite to the current one, every rung signed, with an independent time proof planned for each.

05 · VERIFY · DECADES ON

Today's receipt still checks.

A verifier decades on checks the original signatures under their original rules, then checks the renewal chain from that suite to the present. Both must hold.

03 The archive profile

A slow, strong signature, used sparingly.

SLH-DSA (FIPS 205) is a stateless hash-based signature. Its security rests on hash functions alone, a much more conservative assumption than any other public-key scheme. The price is size and speed: signatures are large and slow to produce.

So R+15 uses it only on checkpoints, registry roots and archive manifests, never per receipt. A single signature over a manifest protects every receipt the manifest covers.

The archive signature is a named suite in the R-Series engine, settled before anything is signed under it. Wiring it into the engine is in development.

Signed under the archive suite	Not signed under the archive suite
Archive manifests	Individual receipts (they keep Ed25519 + ML-DSA-65)
Log checkpoints	Operational API calls and handshakes
Registry roots	Anything that needs to be fast and small

04 The renewal ladder

Signed renewal, rung by rung.

THE RECEIPT

What a renewal signs

Modelled on the Evidence Record Syntax (ERS) pattern for long-term archives.

The range renewed
The suite being sealed over, and the suite doing the sealing
An independent time reference for the renewal
Cosignatures from outside parties who saw it

THE RULE

Renew, don't extend

The receipt envelope is closed: it refuses unknown fields. So a future signature scheme will not be bolted onto old receipts. It arrives as a new schema version, and signed renewals carry the old receipts forward.

Originals are never modified or re-signed
The renewal vector: a chain under suite A, renewed under suite B, with the originals still verifying
Renewal receipts are pinned to the archive profile; anything else is refused

The renewal service is in development. No long-term retention commitment is offered until it is in production.

05 Witnessed checkpoints and dual hash

Nobody has to trust our copy alone.

CHECKPOINTS

Standard format

Log checkpoints follow the C2SP tlog-checkpoint format used by public transparency logs, so existing tooling and witness networks can read them.

WITNESS

Independent cosignatures

A witness signs with its own key, refuses forked histories and refuses replays. Cosignature by an independent operator is in development.

In development

DUAL HASH

Two hashes, manifests only

Archive manifests carry two hashes from different design families, so a future weakness in one does not break the archive. Receipts keep a single hash.

06 Where it stands

In development.

R+15 is in development and is not yet used in production. Archive signing, independent witness cosignatures and the renewal service come into production only after independent certification. In development — talk to us about a design partnership.

In development

07 Questions

What reviewers ask.

Why not sign every receipt with SLH-DSA?

Hash-based signatures are large and slow. One signature over an archive manifest protects every receipt it covers, at a fraction of the cost. Receipts keep their fast hybrid signatures.

Do you re-sign old receipts when algorithms change?

No. Originals are never touched. A renewal receipt seals over a range of them under a newer suite, and the verifier checks both the originals and the renewal chain.

Who are the external witnesses?

At least one witness we do not operate. The intended route is an existing public witness network.

Can we buy long-term evidence retention now?

No. A renewal service and any multi-year retention commitment wait until the archive suite is in production and has passed independent certification.

What has this got to do with satellites?

The same layer that keeps evidence valid over decades also keeps it valid across a lost link, which matters for space and autonomous systems. See space and autonomous systems.

Built for the people who check it in twenty years.

R+15 keeps today's evidence verifiable after the algorithms that signed it have retired.

The fifteen layers Back to R+13

Want the details for your sector? Book a briefing — we share the full design and a live demo in a private session.

Evidence that outlives its algorithms.