Append-only Merkle log

Adjudon Tessera

Public read-only transparency log holding cryptographic commitments to AI-decision audit trails. Signed checkpoints in the c2sp.org/tlog-checkpoint format, retrievable through the standard c2sp.org/tlog-tiles HTTP API. Operated by Adjudon as the evidence chain referenced by EU AI Act Article 12 (logging) and Article 13 (transparency).

What this log holds

Two namespaces share the same Merkle tree:

decision: Cryptographic commitments to individual AI decisions made by Adjudon's customers. Read by claimants, the AI Office, BaFin, and court-appointed experts who need to confirm that a given decision was committed at the timestamp claimed and has not been altered since.
operations: Cryptographic commitments to platform-relevant events: policy changes, key rotations, incident declarations. Read by SOC 2 auditors and DORA Article 28 + 30 operational-risk reviewers (BaFin-supervised entities).

Stored content is restricted to hashes and signatures. No decision content, no personal data, no trace payloads ever reach this service. The mapping from a hash on this log back to an underlying decision is held in Adjudon's customer systems and disclosed bilaterally on lawful request.

Operating facts

Wire format: c2sp.org/tlog-checkpoint — Ed25519, single signer
HTTP API: c2sp.org/tlog-tiles plus a JSON wrapper for Adjudon's backend and witness operators
Region: Frankfurt eu-central-1 — storage and signing key never leave the EU
Operator: Adjudon, Köln, Germany — compliance@adjudon.com

Live endpoints

Standard tlog-tiles

/decision/checkpoint: latest signed STH — decision chain
/operations/checkpoint: latest signed STH — operations chain
/{ns}/tile/<L>/<N>: Merkle tile at level L, index N (example: /decision/tile/0/000)
/{ns}/tile/entries/<N>: entry bundle at index N (example: /decision/tile/entries/000)

Adjudon JSON wrapper

/api/v1/sth/{ns}: STH as JSON (same content, easier to parse)
/api/v1/inclusion-proof: ?namespace=&index= (example: ?namespace=decision&index=0)
/api/v1/consistency-proof: ?namespace=&oldSize= (example: ?namespace=decision&oldSize=1)

Operations

/healthz: service health (Fly + monitoring)

Verifier key

Ed25519 public key for every checkpoint this service signs. Permanent: rotating it would invalidate every prior signature, which would defeat the point of the log.

tessera.adjudon.com+f64bee39+…

Full key file: adjudon.com/keys/tessera-public.txt

Verify offline

The checkpoint is in c2sp.org/signed-note format. Any signed-note verifier reads it — no Adjudon account, no API key. Reference recipe with the Go standard library:

$ curl https://tessera.adjudon.com/decision/checkpoint > cp.txt
$ note verify --keys https://adjudon.com/keys/tessera-public.txt cp.txt

Compatible verifiers ship with golang.org/x/mod/sumdb/note and the Sigstore / transparency.dev tooling.

For witnesses, auditors, court experts

If you operate a public witness against this log, audit a customer of Adjudon, or have been appointed by a court to verify a specific entry: write us. We hand over the verifier key, sample bundles, the inclusion-proof procedure, and the protocol for binding a hash on this log to an underlying decision through the customer concerned.

Witness onboarding: compliance@adjudon.com
Security disclosure: security@adjudon.com