We want to prove some data existed at a certain point and time, we call this Proof of Existence. We can do that by finding the cryptographic hash of some data, then inserting that hash into the Bitcoin blockchain. Since the Bitcoin blockchain is an immutable and secure public ledger, we can prove that the data existed at the time of insertion, like a mathematical notary. Unfortunately that insertion costs money, around $0.03, so it becomes expensive if I wanted to do this for 10,000+ documents.

Instead we can take that data and put it in a Merkle tree, and insert the Merkle root into the Bitcoin blockchain. For any of the items in the Merkle tree, as long as we have the Merkle proof, we can prove that it is contained in that Merkle root notarized in the Bitcoin blockchain.

Therefore we can notarize 10,000 documents for $0.03 instead of $300. It is recommended that the party notarizing their document or data hold on to the Merkle proof "receipt." This allows that party to prove that their document has been notarized in a specific Bitcoin transaction in the absence of any other data.

tldr; A federated server for building blockchain notarized Merkle trees, and returning the Merkle proof as a receipt.

Chainpoint White Paper

• Receipts must be independently verifiable.

A standardized Chainpoint receipt format allows any system to verify a receipt by checking a Bitcoin transaction and using math to verify the data.

{
    "header": {
        "chainpoint_version": "1.0",
        "hash_type": "SHA-256",
        "merkle_root": "6a9a3c86d47f1fe12648c86368ecd9723ff12e3fc34f6ae219d4d9d3e0d60667",
        "tx_id": "012fdc0eb5ebae181e1197b4e9307731473118b0634d3ede749a562e9d11809e",
        "local_timestamp": "1436172703"
    },
    "target": {
        "target_hash": "2f7f9092b2d6c5c17cfe2bcf33fc38a41f2e4d4485b198c2b1074bba067e7168",
        "target_URI": "http://example.org/target_name",
        "target_proof": [
            {
                "left": "e1566f09e0deea437826514431be6e4bdb4fe10aa54d75aecf0b4cdc1bc4320c",
                "parent": "0fdd6b6895e15115c262f6acb9a6ae0c73248568b740454ab21591f8a533dd7f",
                "right": "2f7f9092b2d6c5c17cfe2bcf33fc38a41f2e4d4485b198c2b1074bba067e7168"
            },
            {
                "left": "0fdd6b6895e15115c262f6acb9a6ae0c73248568b740454ab21591f8a533dd7f",
                "parent": "6a9a3c86d47f1fe12648c86368ecd9723ff12e3fc34f6ae219d4d9d3e0d60667",
                "right": "3b7546ed79e3e5a7907381b093c5a182cbf364c5dd0443dfa956c8cca271cc33"
            }
        ]
    },
    "extra": [
        { "custom_key_1": "value_1"},
        { "custom_key_2": "value_2"}
    ]
}

A standardized Chainpoint block is a collection of data items which are summarized and inserted into the Bitcoin blockchain.

{
    "block_num": 1,
    "closed": true,
    "leaves": [
        "e1566f09e0deea437826514431be6e4bdb4fe10aa54d75aecf0b4cdc1bc4320c",
        "2f7f9092b2d6c5c17cfe2bcf33fc38a41f2e4d4485b198c2b1074bba067e7168",
        "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"
    ],
    "merkle_root": "6a9a3c86d47f1fe12648c86368ecd9723ff12e3fc34f6ae219d4d9d3e0d60667",
    "tx_id": "012fdc0eb5ebae181e1197b4e9307731473118b0634d3ede749a562e9d11809e"
}