Etch

Content provenance on a tamper-evident Merkle chain. Register, verify, and prove content existed at a point in time.

pip install etch

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Why Etch?

C2PA embeds provenance in media files. Blockchain attestation services cost gas and take minutes. Etch gives you cryptographic content provenance with a single HTTP call — sub-millisecond, privacy-preserving (content is never stored), and independently verifiable.

Feature	Etch	C2PA	On-chain attestation
Sub-millisecond registration	Yes	N/A (embedded)	No (block time)
Content never stored	Yes	No (embedded in file)	Varies
Offline verification	Yes	Yes	Requires node
No gas fees	Yes	N/A	No
Tamper-evident chain	Yes	Yes	Yes

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Quick start

Start the server

# SQLite (zero config)
uvicorn etch.server:app --reload

# PostgreSQL
ETCH_DATABASE_URL=postgresql://user:pass@localhost/etch uvicorn etch.server:app

Register content

curl -X POST http://localhost:8000/v1/proof \
  -H "Content-Type: application/json" \
  -d '{"content": "My original article text", "label": "Blog: Launch Day"}'

Response:

{
  "proof_id": 0,
  "content_hash": "a3f1...",
  "label": "Blog: Launch Day",
  "timestamp": 1710000000.0,
  "leaf_hash": "...",
  "mmr_root": "...",
  "chain_depth": 1
}

Verify content

curl -X POST http://localhost:8000/v1/proof/0/verify \
  -H "Content-Type: application/json" \
  -d '{"content": "My original article text"}'

Privacy mode (hash only)

# Pre-hash locally — content never leaves your machine
HASH=$(echo -n "secret document" | sha256sum | cut -d' ' -f1)
curl -X POST http://localhost:8000/v1/proof \
  -H "Content-Type: application/json" \
  -d "{\"content_hash\": \"$HASH\"}"

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API

Method	Endpoint	Description
POST	/v1/proof	Register content → proof receipt
GET	/v1/proof/{proof_id}	Retrieve receipt by ID
GET	/v1/proof/hash/{content_hash}	Look up by SHA-256
GET	/v1/proof/recent	List recent proofs (paginated)
GET	/v1/proof/stats	Chain statistics
POST	/v1/proof/{proof_id}/verify	Verify content integrity

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How it works

Etch uses a Merkle Mountain Range (MMR) hash chain. Each proof receipt commits to all previous entries:

leaf_hash = SHA256(prev_root : action_type : payload_hash : timestamp)
mmr_root  = SHA256(prev_root : leaf_hash)

If any historical entry is tampered with, all subsequent hashes become invalid. Proofs can be verified offline — no server trust required.

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As a library

from etch import AuditChain, verify_inclusion_proof

chain = AuditChain()
entry = chain.append("content_proof", {"content_hash": "a3f1..."})

proof = chain.generate_proof(entry.leaf_index)
assert verify_inclusion_proof(proof)  # offline verification

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License

Rising Sun License v1.0. Free for personal use. Commercial deployments connect to the Nous network.