Getting Started with Characters

A Note about Side Channels

The NuCypher network does not store or handle an application’s data; instead - it manages access to application data. Management of encrypted secrets and public keys tends to be highly domain-specific - The surrounding architecture will vary greatly depending on the throughput, sensitivity, and sharing cadence of application secrets. In all cases, NuCypher must be integrated with a storage and transport layer in order to function properly. Along with the transport of ciphertexts, a nucypher application also needs to include channels for Alice and Bob to discover each other’s public keys, and provide policy encrypting information to Bob and Enrico.

Side Channel Application Data

  • Secrets:

    • Message Kits - Encrypted Messages, or “Ciphertexts”

  • Identities:

    • Alice Verifying Key - Public key used for verifying Alice

    • Bob Encrypting Key - Public key used to encrypt for Bob

    • Bob Verifying Key - Public key used to verify Bob

  • Policies:

    • Policy Encrypting Key - Public key used to encrypt messages for a Policy.

    • Labels - A label for specifying a Policy’s target, like a filepath

Running an Ethereum Node

Operation of a decentralized NuCypher character [Alice, Bob, Ursula] requires a connection to an Ethereum node and wallet to interact with smart contracts. For more information about running an Ethereum node, see Using an Ethereum Node.

Connecting to The NuCypher Network

Provider URI

This example uses a local ethereum geth node’s IPC-File specified by provider_uri. By default on ubuntu, the path is ~/.ethereum/geth.ipc - this path will also be logged to the geth-running console on startup.


While the example provided uses Ethereum mainnet, these steps can be followed for the Rinkeby Testnet with updated geth (~/.ethereum/rinkeby/geth.ipc) and seed URI (

Nucypher also supports alternative web3 node providers such as:

  • HTTP(S)-based JSON-RPC server e.g. https://<host>

  • Websocket(Secure)-based JSON-RPC server e.g. ws://<host>:8080, wss://<host>:8080

Connecting Nucypher to an Ethereum Provider

from nucypher.blockchain.eth.interfaces import BlockchainInterfaceFactory

Ursula: Untrusted Re-Encryption Proxies

When initializing an Alice, Bob, or Ursula, an initial “Stranger-Ursula” is needed to perform the role of a Teacher, or “seednode”:

from nucypher.characters.lawful import Ursula

seed_uri = "<SEEDNODE URI>:9151"
seed_uri2 = "<OTHER SEEDNODE URI>:9151"

ursula = Ursula.from_seed_and_stake_info(seed_uri=seed_uri)
another_ursula = Ursula.from_seed_and_stake_info(seed_uri=seed_uri2)

Stranger Ursulas can be created by invoking the from_seed_and_stake_info method, then a list of known_nodes can be passed into any Character’s init. The known_nodes will inform your character of all of the nodes they know about network-wide, then kick-off the automated node-discovery loop:

from nucypher.characters.lawful import Alice
alice = Alice(known_nodes=[ursula, another_ursula], ...)

For information on how to run a staking Ursula node via CLI, see Running a Network Node.

Alice: Grant Access to a Secret

Setup Alice

Create a NuCypher Keyring

from nucypher.config import NucypherKeyring
keyring = NucypherKeyring.generate(checksum_address='0x287A817426DD1AE78ea23e9918e2273b6733a43D', password=PASSWORD)
from nucypher.characters.lawful import Alice, Ursula

ursula = Ursula.from_seed_and_stake_info(seed_uri=<SEEDNODE URI>)

# Unlock Alice's Keyring
keyring = NucypherKeyring(account='0x287A817426DD1AE78ea23e9918e2273b6733a43D')

# Instantiate Alice
alice = Alice(keyring=keyring, known_nodes=[ursula], provider_uri='~/.ethereum/geth.ipc')

# Start Node Discovery

Alice needs to know about Bob in order to grant access by acquiring Bob’s public key’s through the application side channel:

from umbral.keys import UmbralPublicKey

verifying_key = UmbralPublicKey.from_hex(verifying_key),
encrypting_key = UmbralPublicKey.from_hex(encryption_key)


Then, Alice can grant access to Bob:

from nucypher.characters.lawful import Bob
from datetime import timedelta
import maya

bob = Bob.from_public_keys(verifying_key=bob_verifying_key,  encrypting_key=bob_encrypting_key)
policy_end_datetime = + timedelta(days=5)  # Five days from now
policy = alice.grant(bob,
                     label=b'my-secret-stuff',  # Sent to Bob via side channel
                     m=2, n=3,

policy_encrypting_key = policy.public_key

Enrico: Encrypt a Secret

Setup Enrico

First, a policy_encrypting_key must be retrieved from the application side channel, then to encrypt a secret using Enrico:


from nucypher.characters.lawful import Enrico

enrico = Enrico(policy_encrypting_key=policy_encrypting_key)
ciphertext, signature = enrico.encrypt_message(plaintext=b'Peace at dawn.')

The ciphertext can then be sent to Bob via the application side channel.

Note that Alice can get the public key even before creating the policy. From this moment on, any Data Source (Enrico) that knows the public key can encrypt data originally intended for Alice, but can be shared with any Bob that Alice grants access.

policy_pubkey = alice.get_policy_encrypting_key_from_label(label)

Bob: Decrypt a Secret

For Bob to retrieve a secret, the ciphertext, label, policy encrypting key, and Alice’s verifying key must all be fetched from the application side channel. Then, Bob constructs his perspective of the policy’s network actors:

Setup Bob

from nucypher.characters.lawful import Alice, Bob, Enrico, Ursula

# Application Side-Channel
# --------------------------
# label = <Side Channel>
# ciphertext = <Side Channel>
# policy_encrypting_key = <Side Channel>
# alice_verifying_key = <Side Channel>

# Everyone!
ursula = Ursula.from_seed_and_stake_info(seed_uri=<SEEDNODE URI>)
alice = Alice.from_public_keys(verifying_key=alice_verifying_key)
enrico = Enrico(policy_encrypting_key=policy_encrypting_key)

# Generate and unlock Bob's keyring
keyring = NucypherKeyring.generate(checksum_address='0xC080708026a3A280894365Efd51Bb64521c45147', password=PASSWORD)

# Make Bob
bob = Bob(known_nodes=[ursula], checksum_address="0xC080708026a3A280894365Efd51Bb64521c45147")

Join a Policy

Next, Bob needs to join the policy:

bob.join_policy(label=label, alice_verifying_key=alice.public_keys(SigningPower), block=True)

Retrieve and Decrypt

Then Bob can retrieve, and decrypt the ciphertext:

cleartexts = bob.retrieve(label=label,