Building chains

The core abstraction for the a ClaimChain user is a state. The state contains information about the user, and claims they make about other users or objects. Currently, this package only supports private claims, which means the owner of a chain needs to explicitly make every claim readable by intended readers. Once the state is constructed it can be committed to the chain.

Here is how user Alice would prepare her state:

from claimchain import State

state = State()

# Alice adds information about herself
state.identity_info = "Hi, I'm Alice"

# Alice adds private claims
state['bob'] = 'Bob is a good lad'

Making claims accessible requires knowing the DH public key of each authorized reader. The way to obtain the DH keys of other users is described later. Assuming Alice has Carol’s DH public key, carol_dh_pk, she can allow Carol to access her claim about Bob:

state.grant_access(carol_dh_pk, ['bob'])

Note that the second argument must be an iterable of claim labels, not a single label.

To commit the state, first, a chain needs to be built, and second, the cryptographic keys have to be generated:

from hippiehug import Chain
from claimchain import LocalParams, State

state = State()

# Generate cryptographic keys
params = LocalParams.generate()

store = {}
chain = Chain(store)

with params.as_default():
    head = state.commit(chain)

The chain can then be published or transmitted to other users by publishing the store and communicating the chain’s head. Other users will be able to interpret the chain using the View interface, described below.

Interpreting chains

Having access to the store (dictionary) containing other user’s chain, and a head of this user’s chain, one can use the View interface.

Here is how Carol can interpret Alice’s claimchain, assuming Alice’s store is alice_store, the head of her chain is alice_head, and params is Carol’s LocalParams object:

from hippiehug import Chain
from claimchain import View

alice_chain = Chain(alice_store, root_hash=alice_head)

with params.as_default():
    alice_view = View(alice_chain)

    # Try to get claim with label 'bob'
    claim = alice_view['bob']

    assert claim == b'Bob is a good lad'

Finally, this is how Carol can retrieve Alice’s DH public key:

alice_dh_pk = alice_view.params.dh.pk

This DH public key can be later used to grant Alice rights to read claims on Carol’s chain.