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Nijsse-PhD-anchored.pdf
Nijsse-PhD-anchored.pdf
 
 
anchor.sol
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readme.md
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readme.md

A Note on Data Anchoring

Data Anchoring, also known as Digital Archiving or Public Timestamping1, involves writing a cryptographic hash to immutable storage. Public blockchains present an ideal use case for this type of activity as the distributed database ensures data replication and censorship resistance, and the public nature makes verification quick and efficient.

The work has been anchored to popular blockchains by including the hash in a transaction in the appropriate style.

The SHA256 hash of version 1 of this document is:

9885dee02e36e2e4bbf808093364f2dafcc284a119f280417025e64fb5b47215

and can be verified by downloading the PDF file from GitHub, computing the SHA256 hash, for example:

$ shasum -a 256 Nijsse-PhD-anchored.pdf

and comparing the hashed output to the public value found in the blockchain. Any update to a pdf, such as including a transaction hash or block number, will invalidate the hash, so to avoid this issue, a live-update must be provided, exclusive of the original hash creation.

Bitcoin

The OP_RETURN script opcode in a Bitcoin transaction marks the transaction outputs as unspendable, or specifically as a UTXO of type nulldata. Thus, any data in the field terminates the UTXO chain and can be used to burn bitcoin, or, as in this case, store 80 bytes of arbitrary data. Using OP_RETURN is considered more polite than writing data to the pay-to-public-key-hash (p2pkh) output, as it is difficult to distinguish from a real public-key-hash, and so must be stored by all nodes.2 OP_RETURN data can optionally be pruned by nodes to save storage.

The transaction in block 838705 contains the following transaction output, partially shown in JSON, where part of the OP_RETURN is:

"outputs": [
  {
    "address": null,
    "pkscript": "6a209885dee02e36e2e4bbf808093364f2dafcc284a119f280417025e64fb5b47215",
    "value": 0,
    "spent": false,
    "spender": null
  }
]

The end of the pkscript value matches the SHA256 output.

Ethereum

Smart contract functionality allows for more versatile storage in Ethereum. One method is to deploy a contract that contains some data that can be retrieved later by calling the contract. An alternate method is to use the logging capability in the data field of a transaction that will write log data to the transaction receipt.

A contract is deployed to Ethereum at:

0x975A313f03a56d232D9353830D8930481CFf5e1f

which accepts a 32 byte hash and a message:

addHash(bytes32 _hash, string calldata _message)

In block 19666573, the transaction contains the hash above (prepended with 0x) and the message: 'Nijsse-PhD-data-anchor'.

Footnotes

  1. Haber, S., & Stornetta, W. S. (1991). How to Time-Stamp a Digital Document. In A. J. Menezes & S. A. Vanstone (Eds.), Advances in Cryptology-CRYPTO '90 (pp. 437–455). Springer. DOI: 10.1007/3-540-38424-3_32 ↩

  2. Bartoletti, M., & Pompianu, L. (2017). An analysis of Bitcoin OP_RETURN metadata. arXiv: 1702.01024 ↩