Evidence kinds/Ed25519 attestation

Ed25519 attestation

cryptographic evidence

Per-entry Ed25519 signature using the operator's workspace signing key.

What it is

Each L12 entry includes an Ed25519 signature over the canonical form of the entry. The signature is generated using the operator's workspace signing key — held by the operator, never escrowed by Promethean.

On signup, the workspace generates an Ed25519 keypair locally. The private seed stays operator-side; the public key is published in the workspace identity (workspace.json in the audit bundle) and serves as the trust anchor for chain verification.

Ed25519 was chosen for: deterministic signatures (no entropy required at sign time), small signature size (64 bytes), high performance, mature implementations in every major language. The standard is RFC 8032.

What it guarantees

  • Per-entry signature verifiability against published public key.
  • Operator-managed private key — no Promethean-side custody.
  • Cryptographic standard implementation (RFC 8032).
  • Deterministic — same input + key produces same signature byte-for-byte.

What it does NOT guarantee

Honest limits. Every primitive has them.

  • Key-rotation hygiene — that's operator's key-management process.
  • Resistance to operator-side key compromise — if the private seed leaks, signatures can be forged.
  • HSM-grade key storage by default — Scale + Enterprise tiers add HSM hooks; lower tiers store keys in the operator's environment.

Regulations that engage this kind

GDPR Art. 32

Integrity of processing

HIPAA §164.312(c)

Integrity controls

NIS2 Art. 21(2)(h)

Cryptography + encryption requirements

Sectors that rely on this kind

Related evidence kinds

L12 receipt chain

Hash-chained, Ed25519-signed log of every LLM-in-the-loop decision a Promethean-built product makes.

Operator-managed signing key

The Ed25519 private signing key is generated + held operator-side, never escrowed by Promethean.

FAQ

What if we lose our signing key?

Lost private key = unrecoverable signing capability for that workspace. Previously-signed entries remain verifiable (public key is preserved). Future entries require key-rotation: generate new keypair, publish new public key in workspace identity, begin signing under new key. The chain shows the rotation explicitly (operator-friendly, regulator-friendly).