We need to clearly define how to serialize a json object to calculate the hash.

The serialization should produce the same byte output independently of the architecture running the software. If there are diferences in the serialization hash validations will fail altough the transaction is correct

Example

a = r.expr({'a': 1}).to_json().run(b.connection)
u'{"a":1}'

b = json.dumps({'a': 1})
'{"a": 1}'

a == b
False

We should provide the serialization and deserialization so that the following is always true.

Example

deserialize(serialize(data)) == data
True

Standard serialization for the bigchain

After looking at this further I think that the python json module is still the best bet because it complies with the RFC. We can specify the encoding, separators used and enforce it to order by the keys to make sure that we obtain maximum interopelability.

import json

json.dumps(data, skipkeys=False, ensure_ascii=False, encoding="utf-8",
           separators=(',', ':'), sort_keys=True)

• skipkeys: With skipkeys False if the provided keys are not a string the serialization will fail. This way we enforce all keys to be strings
• ensure_ascii: The RFC recommends utf-8 for maximum interoperability. By setting ensure_ascii to False we allow unicode characters and force the encoding to utf-8.
• separators: We need to define a standard separator to use in the serialization. We did not do this different implementations could use different separators for serialization resulting in a still valid transaction but with a different hash e. g. an extra whitespace introduced in the serialization would not still create a valid json object but the hash would be different

Example

Everytime we need to perform some operation on the data like calculating the hash or signing/verifying the transaction we need to use the previous criteria to serialize the data and then use the byte representation of the serialized data (if we threat the data as bytes we eliminate possible enconding errors e.g. unicode characters)

# calculate the hash of a transaction
# the transaction is a dictionary
tx_serialized = bytes(serialize(tx))
tx_hash = hashlib.sha3_256(tx_serialized).hexdigest()

# signing a transaction
tx_serialized = bytes(serialize(tx))
signature = sk.sign(tx_serialized)

# verify signature
tx_serialized = bytes(serialize(tx))
vk.verify(signature, tx_serialized)