Local verification

The whole point of the SDKs is trustless verification: an auditor recomputes the proof and compares it with the root anchored on the blockchain, never trusting the API’s answer.

The shared scheme (v2)

Every implementation — the Go server, the Go SDK, and the Python SDK — computes a record’s hash identically:

SHA-256( 0x00 ‖ lp(id) ‖ lp(timestamp) ‖ lp(source) ‖ lp(canonical(payload)) )

• lp(x) is an 8-byte big-endian length followed by x, so content cannot shift across field boundaries undetected.
• 0x00 tags a Merkle leaf; internal nodes are tagged 0x01 — domain separation that closes a class of Merkle attacks (CVE-2012-2459).
• canonical(payload) matches Go’s encoding/json (sorted keys, compact, HTML-escaped), so hashes are byte-identical across languages.
• hash_fields, when set, restricts which payload keys feed the hash.
• hash_version selects the scheme (absent = legacy v1), so old batches still verify after an upgrade.

Cross-language number parity

Payload numbers are decoded as 64-bit floats server-side, so integer-valued numbers canonicalize without a decimal point (7, not 7.0). For guaranteed parity across languages, prefer integers and strings in payloads.

The verification step

1. Recompute each record’s hash with the scheme above.
2. Fold the ordered hashes into a Merkle tree (odd nodes are promoted, not duplicated).
3. Compare the recomputed root with the root read from Fabric (or returned by the /public/anchors/{batchId} endpoint).

A match proves the records are exactly what was anchored. A mismatch proves something changed. See cryptographic design for the full rationale.