The WORM ledger guarantees that records cannot be modified or deleted after they are written. Verification confirms that guarantee holds for a specific entry: that the hash chain is intact and that no post-write alteration occurred. This guide covers verification using the service-fs API and the standard SHA-256 toolchain — no proprietary tooling is required.

For what the WORM guarantee covers and does not cover, see worm-ledger-architecture. For the storage format, see worm-ledger-storage-architecture.

Prerequisites

• Access to a Totebox ledger (local file access or service-fs API)
• A SHA-256 utility (sha256sum on Linux, shasum -a 256 on macOS, or equivalent)
• The position (row index) or timestamp range of the entry you want to verify

Step 1: Export the tile containing your entry

Using the service-fs API, call read_since with the checkpoint immediately preceding your target entry:

read_since(checkpoint_id: "<checkpoint-id>", limit: 1)

This returns the tile file for that segment of the ledger. On a local deployment you can also read the C2SP tlog-tiles files directly from the ledger directory.

Step 2: Locate the entry in the tile

The tile is plain text in C2SP tlog-tiles format. Each line is a base64-encoded log entry followed by its hash. Find the row matching your target entry by timestamp or sequence number.

Step 3: Verify the hash chain

For each row in the tile, the hash of that row is included in the hash computation for the next row. To verify entry N:

1. Take the hash from row N−1 (or the genesis hash for the first entry).
2. Concatenate it with the raw bytes of entry N.
3. Compute SHA-256 of the concatenation.
4. Compare the result to the hash recorded in row N.

A match confirms the chain is intact from the genesis to that point. A mismatch at row N means either row N or some earlier row was altered — inspect each row backwards from N to isolate the point of tampering.

Step 4: Verify against a signed checkpoint

If a signed checkpoint covers the range containing your entry, you can verify that checkpoint's signature to extend the guarantee to the anchor point:

1. Retrieve the C2SP signed-note for the relevant checkpoint.
2. Verify the note's Ed25519 signature using the public key published for the Sigstore Rekor anchor.
3. Confirm that the checkpoint covers a sequence number that includes your entry.

A valid signature from Sigstore Rekor means the chain state was externally timestamped at that point, providing verifiability independent of the live service.

Automated verification

The service-fs CLI provides a verify subcommand that runs steps 2–4 automatically:

service-fs verify --from <checkpoint-id> --to <entry-id>

Use the manual procedure above when you want to inspect the chain without trusting the CLI.

Key takeaways

• Verification requires only a SHA-256 utility and the raw tile files — no live service needed
• A mismatch in the hash chain at row N means alteration at or before N; inspect backwards to isolate it
• Signed checkpoints extend verification to a public timestamp anchor, enabling third-party audits
• The C2SP tlog-tiles format ensures these steps remain executable with standard tools for decades

See also

• worm-ledger-architecture — what the WORM guarantee covers and its structural properties
• worm-ledger-storage-architecture — the tile format, atomic writes, and checkpoint structure
• service-fs-architecture — the service that implements and serves the ledger
• read-the-command-ledger — reading ledger entries from within os-console
• worm-ledger-design — the design philosophy and regulatory compliance rationale