Code examples

Create the following two files:

notarizer.py

import hashlib
import os.path
import requests
import sys

# The base URL of the notary service API.
base_url = 'https://eu2-cloud.acronis.com/api/notary/v2'
# The authentication header for accessing the API.
# The value after 'Bearer' is the token generated in "Accessing the API".
auth = {
    'Authorization': 'Bearer 8770b34b74f9e4d9424eff50c38182bb4ae7f5596582ae61900b1b6a23e3ec58'
}


def calculate_file_hash(file_path):
    """Calculates the SHA-256 hash value of file contents."""

    with open(file_path, 'rb') as fd:
        sha256 = hashlib.sha256()
        chunk = fd.read(128 * sha256.block_size)
        while chunk:
            sha256.update(chunk)
            chunk = fd.read(128 * sha256.block_size)
        return sha256.hexdigest()


def notarize(file_path):
    """
    Notarizes a file by calculating its hash and sending the hash to the notary service.
    """

    # Create the meta object with the file name and calculated hash value.
    metadata = {
        'GUID': os.path.basename(file_path),
        'eTag': calculate_file_hash(file_path),
    }

    # Post the object to the notary service. The same object may be posted to the service
    # multiple times and every time a new certificate is created.
    try:
        response = requests.post(f'{base_url}/meta', headers=auth, json=metadata)
    except requests.ConnectionError:
        print('No connection to the notary service.',
              'Try again later or contact your service administrator.')
        return

    # Check for errors.
    status_code = response.status_code
    if status_code == 401:
        print('Not authorized.')
        return
    if status_code == 402:
        print('The "Notarizations" quota is reached.')
        return
    if status_code != 200:
        print(response.status_code, response.reason)
        return

    # Convert the JSON text that the response body contains to an object, and then print the ID of the created notarization certificate.
    print(response.json()['certificate_id'])


if __name__ == '__main__':
    notarize(sys.argv[1])

verifier.py

import hashlib
import pprint
import requests
import sys

# The base URL of the notary service API.
base_url = 'https://eu2-cloud.acronis.com/api/notary/v2'


def calculate_file_hash(file_path):
    """Calculates the SHA-256 hash value of file contents."""

    with open(file_path, 'rb') as fd:
        sha256 = hashlib.sha256()
        chunk = fd.read(128 * sha256.block_size)
        while chunk:
            sha256.update(chunk)
            chunk = fd.read(128 * sha256.block_size)
        return sha256.hexdigest()


def verify(file_path, certificate_id):
    """
    Verifies if a file is notarized by calculating its hash and checking if
    this hash was written to the Ethereum blockchain during a specific notarization
    process designated by the notarization certificate ID.
    """

    # Create the meta object with the file name and calculated hash value.
    file_hash_data = {
        'hash': calculate_file_hash(file_path),
        'certificate_hash': certificate_id,
    }

    # Post the object to the notary service.
    try:
        response = requests.post(f'{base_url}/hashes/verify', json=file_hash_data)
    except requests.ConnectionError:
        print('No connection to the notary service.',
              'Try again later or contact your service administrator.')
        return

    # Check for errors.
    status_code = response.status_code
    if status_code == 404:
        print('This file has never been notarized.')
        return
    if status_code != 200:
        print(response.status_code, response.reason)
        return

    # Convert the JSON text that the response body contains to an object,
    # and then fetch the notarization certificate.
    certificate = response.json()['certificates'][0]

    if not certificate['txid']:
        print('The file notarization is in progress.')
        return

    print('The file is notarized.')
    pprint.pprint(certificate)


if __name__ == '__main__':
    verify(sys.argv[1], sys.argv[2])

To notarize a file

1. Start the command line, and then cd to the file’s folder.

2. Run the following command:

   python notarizer.py <file name>
   

   If no error occurs, the script will output the ID of the notarization certificate that has been created. Otherwise, the script will output the error details.

Use the returned ID, along with the file itself, to verify the file’s authenticity.

To verify the authenticity of a file

1. Start the command line, and then cd to the file’s folder.

2. Run the following command:

   python verifier.py <file name> <notarization certificate ID>
   

   The script will output the file notarization status or error details, if any.