remote-signing.py

import json
from pprint import pprint

import base58
import sha3
from cryptoconditions import Ed25519Sha256

from bigchaindb_driver.crypto import generate_keypair


remote = generate_keypair()

# The public key is known by the client
public_key = remote.public_key

# While the private key is securely stored in the server
private_key = remote.private_key


# The client prepares the transaction
operation = 'CREATE'

version = '2.0'

asset = {
    'data': {
        'bicycle': {
            'manufacturer': 'bkfab',
            'serial_number': 'abcd1234',
        },
    },
}

metadata = {'planet': 'earth'}

ed25519 = Ed25519Sha256(public_key=base58.b58decode(public_key))

output = {
    'amount': '1',
    'condition': {
        'details': {
            'type': ed25519.TYPE_NAME,
            'public_key': base58.b58encode(ed25519.public_key),
        },
        'uri': ed25519.condition_uri,
    },
    'public_keys': [public_key,],
}
outputs = [output,]

input_ = {
    'fulfillment': None,
    'fulfills': None,
    'owners_before': [public_key,]
}
inputs = (input_,)

handcrafted_creation_tx = {
    'asset': asset,
    'metadata': metadata,
    'operation': operation,
    'outputs': outputs,
    'inputs': inputs,
    'version': version,
    'id': None,
}

message = json.dumps(
    handcrafted_creation_tx,
    sort_keys=True,
    separators=(',', ':'),
    ensure_ascii=False,
)

message = sha3.sha3_256(message.encode()).digest()


# At this point, the client makes an HTTP request to sign the message.
# The server implements the following code, and returns the signature.
from nacl.signing import VerifyKey, SigningKey
sk = SigningKey(base58.b58decode(private_key))
signature = sk.sign(message).signature



# After getting the signature, the client can fulfill the transaction.
ed25519.signature = signature

fulfillment_uri = ed25519.serialize_uri()
handcrafted_creation_tx['inputs'][0]['fulfillment'] = fulfillment_uri

json_str_tx = json.dumps(
    handcrafted_creation_tx,
    sort_keys=True,
    separators=(',', ':'),
    ensure_ascii=False,
)

creation_txid = sha3.sha3_256(json_str_tx.encode()).hexdigest()

handcrafted_creation_tx['id'] = creation_txid


# Extra: validate the signature in the transaction.
#
# Transaction validation is a three step process:
# 1. schema validation checks the structure of the transaction
# 2. signature validation checks the signature
# 3. spends validation checks if the inputs of the transaction are valid and
# can be spent.
# Note: in this snippet we skip step 3
from bigchaindb.models import Transaction

# Step 1: check the transaction schema
transaction = Transaction.from_dict(handcrafted_creation_tx)

# Step 2: check the signature
# `inputs_valid` checks *only* the signature:
# enabling full validation would require to query the database as well,
# but for this use case we can skip it.
if transaction.inputs_valid():
    print('The transaction is VALID')
    print()
else:
    print('ERROR: Transaction is INVALID')
    print()

pprint(handcrafted_creation_tx)