Getting Started with Characters¶
A Note about Side Channels¶
The PRE Application nodes do 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, the PRE Application 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.
The Application Side Channel¶
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
Choosing an Ethereum Provider¶
Operation of a decentralized NuCypher character [Alice
, Bob
, Ursula
] requires
a connection to an Ethereum node and wallet to interact with smart contracts.
For general background information about choosing a node technology and node operation, see https://web3py.readthedocs.io/en/stable/node.html.
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)
Note
While any PRE node can be used to seed your peers, NuCypher maintains workers that can be used as seed nodes:
mainnet:
https://mainnet.nucypher.network:9151
lynx:
https://lynx.nucypher.network:9151
tapir:
https://tapir.nucypher.network:9151
seed_uri = 'https://lynx.nucypher.network:9151'
ursula = Ursula.from_seed_and_stake_info(seed_uri=seed_uri)
Stranger Ursula
s 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 Node.
Alice: Grant Access to a Secret¶
Setup Alice Keys¶
Alice uses an ethereum wallet to create publish access control policies to the ethereum blockchain, and a set of related keys derived from a “nucypher keystore”.
First, instantiate a Signer
to use for signing transactions. This is an API for Alice’s ethereum
wallet, which can be an keystore file.
Keystore directory or keyfile:
'keystore://<ABSOLUTE PATH TO KEYSTORE>'
Here are some examples of usage:
from nucypher.blockchain.eth.signers import Signer
wallet = Signer.from_signer_uri('<YOUR SIGNER URI>')
software_wallet = Signer.from_signer_uri('keystore:///home/user/.ethereum/keystore/<KEY FILENAME>')
If you are using a software wallet, be sure to unlock it:
# Unlocking a software wallet
>>> software_wallet.unlock_account(account='0x287A817426DD1AE78ea23e9918e2273b6733a43D', password=<ETH_PASSWORD>)
Next, create a NuCypher Keystore. This step will generate a new set of related private keys used for nucypher cryptography operations,
which can be integrated into your application’s user on-boarding or setup logic. These keys will be stored on the disk,
encrypted-at-rest using the supplied password. Use the same account as the signer; Keystores are timestamped and named by public key,
so be sure to specify an account you control with a Signer
.
from nucypher.crypto.keystore import Keystore
keystore = Keystore.generate(password=NEW_PASSWORD) # used to encrypt nucypher private keys
# Public Key
>>> keystore.id
e76f101f35846f18d80bfda5c61e9ec2
# The root directory containing the private keys
>>> keystore.keystore_dir
'/home/user/.local/share/nucypher/keystore'
After generating a keystore, any future usage can decrypt the keys from the disk:
from nucypher.crypto.keystore import Keystore
# Restore an existing Alice keystore
path = '/home/user/.local/share/nucypher/keystore/1621399628-e76f101f35846f18d80bfda5c61e9ec2.priv'
keystore = Keystore(path)
# Unlock Alice's keystore
keystore.unlock(password=NUCYPHER_PASSWORD)
from nucypher.characters.lawful import Alice, Ursula
# Instantiate a default peer (optional)
ursula = Ursula.from_seed_and_stake_info(seed_uri='https://tapir.nucypher.network:9151')
# Instantiate Alice
alice = Alice(
keystore=keystore, # NuCypher Keystore
known_nodes=[ursula], # Peers (Optional)
signer=signer, # Alice Wallet
eth_provider_uri=<RPC ENDPOINT>, # Ethereum RPC endpoint
domain='tapir' # PRE Application network (mainnet, lynx, tapir)
)
# Alice is identified by her ethereum address
alice.checksum_address
'0x287A817426DD1AE78ea23e9918e2273b6733a43D'
# Start node discovery
alice.start_learning_loop(now=True)
Alice needs to know Bob’s public keys in order to grant him access. Alice’s are expected to acquiring Bob’s public keys through the application side channel. Umbral public keys used in NuCypher’s proxy re-encryption can be restored from hex for API usage:
from umbral.keys import UmbralPublicKey
verifying_key = UmbralPublicKey.from_hex(verifying_key_as_hex),
encrypting_key = UmbralPublicKey.from_hex(encryption_key_as_hex)
Grant¶
Alice can grant access to Bob using his public keys:
from umbral.keys import UmbralPublicKey
from nucypher.characters.lawful import Bob
from datetime import timedelta
from web3 import Web3
import maya
# Deserialize bob's public keys from the application side-channel
verifying_key = UmbralPublicKey.from_hex(verifying_key_as_hex),
encrypting_key = UmbralPublicKey.from_hex(encryption_key_as_hex)
# Make a representation of Bob
bob = Bob.from_public_keys(verifying_key=bob_verifying_key, encrypting_key=bob_encrypting_key)
policy = alice.grant(
bob,
label=b'my-secret-stuff', # Send to Bob via side channel
threshold=2, # Threshold shares for access
shares=3, # Total nodes with shares
rate=Web3.toWei(50, 'gwei'), # 50 Gwei is the minimum rate (per node per period)
expiration= maya.now() + timedelta(days=5) # Five days from now
)
# The policy's public key
policy_encrypting_key = policy.public_key
Putting it all together, here’s an example starter script for granting access using a software wallet and an existing keystore:
from nucypher.blockchain.eth.signers import Signer
from nucypher.crypto.keystore import Keystore
from nucypher.characters.lawful import Alice, Bob
from umbral.keys import UmbralPublicKey
from datetime import timedelta
from web3 import Web3
import maya
# Restore Existing NuCypher Keystore
keystore = Keystore(keystore_path=path)
keystore.unlock('YOUR KEYSTORE PASSWORD')
# Ethereum Software Wallet
wallet = Signer.from_signer_uri("keystore:///home/user/.ethereum/goerli/keystore/UTC--2021...0278ad02...')
wallet.unlock_account('0x287A817426DD1AE78ea23e9918e2273b6733a43D', 'SOFTWARE WALLET PASSWORD')
# Make Alice
alice = Alice(
domain='tapir', # testnet
eth_provider_uri='GOERLI RPC ENDPOINT',
keystore=keystore,
signer=wallet,
)
# From Public Key Side Channel
verifying_key = UmbralPublicKey.from_hex('0278ad02da8083aea357a8ed675dcc0b6e9c78557c506ea10b102b4b282c006b12')
encrypting_key = UmbralPublicKey.from_hex('03ec6b4e1f2b7d06ac544dde86730f9a4047e80a0a4d3c1566e88afe4bb449bdd9')
# Make Stranger-Bob
bob = Bob.from_public_keys(verifying_key=verifying_key, encrypting_key=encrypting_key)
# Grant Bob Access
policy = alice.grant(
bob,
label=b'my-secret-stuff', # Send to Bob via side channel
threshold=2, # Threshold shares for access
shares=3, # Total nodes with shares
rate=Web3.toWei(50, 'gwei'), # 50 Gwei is the minimum rate (per node per period)
expiration= maya.now() + timedelta(days=5) # Five days from now
)
Enrico: Encrypt a Secret¶
First, a policy_encrypting_key
must be retrieved from the application side channel, then
to encrypt a secret using Enrico:
Encrypt¶
from nucypher.characters.lawful import Enrico
enrico = Enrico(policy_encrypting_key=policy_encrypting_key)
message_kit = enrico.encrypt_message(plaintext=b'Peace at dawn.')
The message kit 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 message kit, 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¶
Bob’s setup is similar to Alice’s above.
from nucypher.characters.lawful import Alice, Bob, Enrico, Ursula
# Application Side-Channel
# --------------------------
# encrypted_treasure_map = <Side Channel>
# message_kit = <Side Channel>
# policy_encrypting_key = <Side Channel>
# alice_verifying_key = <Side Channel>
# Everyone!
ursula = Ursula.from_seed_and_stake_info(seed_uri='https://tapir.nucypher.network:9151')
alice = Alice.from_public_keys(verifying_key=alice_verifying_key)
enrico = Enrico(policy_encrypting_key=policy_encrypting_key)
# Restore Existing Bob keystore
keystore = Keystore(keystore_path=path)
# Unlock keystore and make Bob
keystore.unlock(PASSWORD)
bob = Bob(
keystore=keystore,
known_nodes=[ursula],
domain='tapir'
)
Retrieve and Decrypt¶
Then Bob can retrieve and decrypt the message kit:
cleartexts = bob.retrieve_and_decrypt(
message_kits=[message_kit],
alice_verifying_key=alice_public_key,
encrypted_treasure_map=policy.treasure_map,
)