Proof of Time

Idea is to create a service that can guarantee that someone had a file in its current state at some point in time. This can be done by making a json string with the digest of the file, and the time it was created. This string can then be signed. The signature and info can then be packaged in as a json string and passed back to the requester.

Guarantee

The package guarantees that the doc existed at the UTC datetime listed IF:

• the digest matches that of the file it is guaranteeing
• the signature can be verified against the JSON stringified representation of the 'info' block (see below)
• the verification is done using the site's public key

Package

The generated package has the following form:

{
  "info": {
    "datetime": "UTC datetime",
    "digest": "SHA3-256 digest of file"
  },
  "signature": "Ed448 signature of the above 'info' block",
  "public_key": "Optional, public key to check signature without returning to the site",
  "message": "Optional, message passed with package creation request (ex. 'proof for doc X')"
}

Usage

It is intended that the code is used to make several AWS Lambda functions. These are one to create the key, one to create a package, and one to verify a package. To configure this do the following:

• Generate a layer that contains the dependency cryptography built for the Lambda environment
  • This can be done using this code
• Create a function for creating the key, creating a package, and verifying a package
• Assemble and upload the code for the functions by running prepare_functions.sh
• For the first grant it permission to create a secret named pit_secret
  • NOTE: Don't grant it permission to modify or delete secrets to prevent accidental overwriting
• For the other two grant permission to read the secret and add the environment variable secret_name as pit_secret
• Upload and add the layer to each of them
• Specify the handler for each of the functions (i.e. lambda_handler.lambda_handler -> FILE_NAME.handler)

Future features

• Cache secret between invocations