"""Cryptography functions used by BasicWallet."""
import re
from collections import OrderedDict
from typing import Callable, Optional, Sequence, Tuple, Union, List
import nacl.bindings
import nacl.exceptions
import nacl.utils
from marshmallow import ValidationError
from ..utils.jwe import JweRecipient, b64url, JweEnvelope, from_b64url
from .error import WalletError
from .util import bytes_to_b58, b64_to_bytes, b58_to_bytes, random_seed
from .key_type import ED25519, BLS12381G2, KeyType
from .bbs import (
create_bls12381g2_keypair,
verify_signed_messages_bls12381g2,
BbsException,
sign_messages_bls12381g2,
)
[docs]def create_keypair(key_type: KeyType, seed: bytes = None) -> Tuple[bytes, bytes]:
"""Create a public and private keypair from a seed value.
Args:
key_type: The type of key to generate
seed: Seed for keypair
Raises:
WalletError: If the key type is not supported
Returns:
A tuple of (public key, secret key)
"""
if key_type == ED25519:
return create_ed25519_keypair(seed)
elif key_type == BLS12381G2:
# This ensures python won't crash if bbs is not installed and not used
return create_bls12381g2_keypair(seed)
else:
raise WalletError(f"Unsupported key type: {key_type.key_type}")
[docs]def create_ed25519_keypair(seed: bytes = None) -> Tuple[bytes, bytes]:
"""Create a public and private ed25519 keypair from a seed value.
Args:
seed: Seed for keypair
Returns:
A tuple of (public key, secret key)
"""
if not seed:
seed = random_seed()
pk, sk = nacl.bindings.crypto_sign_seed_keypair(seed)
return pk, sk
[docs]def seed_to_did(seed: str) -> str:
"""Derive a DID from a seed value.
Args:
seed: The seed to derive
Returns:
The DID derived from the seed
"""
seed = validate_seed(seed)
verkey, _ = create_ed25519_keypair(seed)
did = bytes_to_b58(verkey[:16])
return did
[docs]def did_is_self_certified(did: str, verkey: str) -> bool:
"""Check if the DID is self certified.
Args:
did: DID string
verkey: VERKEY string
"""
ABBREVIATED_VERKEY_REGEX = "^~[1-9A-HJ-NP-Za-km-z]{21,22}$"
if re.search(ABBREVIATED_VERKEY_REGEX, verkey):
return True
verkey_bytes = b58_to_bytes(verkey)
did_from_verkey = bytes_to_b58(verkey_bytes[:16])
if did == did_from_verkey:
return True
return False
[docs]def sign_pk_from_sk(secret: bytes) -> bytes:
"""Extract the verkey from a secret signing key."""
seed_len = nacl.bindings.crypto_sign_SEEDBYTES
return secret[seed_len:]
[docs]def validate_seed(seed: Union[str, bytes, None]) -> bytes:
"""Convert a seed parameter to standard format and check length.
Args:
seed: The seed to validate
Returns:
The validated and encoded seed
"""
if not seed:
return None
if isinstance(seed, str):
if "=" in seed:
seed = b64_to_bytes(seed)
else:
seed = seed.encode("ascii")
if not isinstance(seed, bytes):
raise WalletError("Seed value is not a string or bytes")
if len(seed) != 32:
raise WalletError("Seed value must be 32 bytes in length")
return seed
[docs]def sign_message(
message: Union[List[bytes], bytes], secret: bytes, key_type: KeyType
) -> bytes:
"""Sign message(s) using a private signing key.
Args:
message: The message(s) to sign
secret: The private signing key
key_type: The key type to derive the signature algorithm from
Returns:
bytes: The signature
"""
# Make messages list if not already for easier checking going forward
messages = message if isinstance(message, list) else [message]
if key_type == ED25519:
if len(messages) > 1:
raise WalletError("ed25519 can only sign a single message")
return sign_message_ed25519(
message=messages[0],
secret=secret,
)
elif key_type == BLS12381G2:
return sign_messages_bls12381g2(messages=messages, secret=secret)
else:
raise WalletError(f"Unsupported key type: {key_type.key_type}")
[docs]def sign_message_ed25519(message: bytes, secret: bytes) -> bytes:
"""Sign message using a ed25519 private signing key.
Args:
messages (bytes): The message to sign
secret (bytes): The private signing key
Returns:
bytes: The signature
"""
result = nacl.bindings.crypto_sign(message, secret)
sig = result[: nacl.bindings.crypto_sign_BYTES]
return sig
[docs]def verify_signed_message(
message: Union[List[bytes], bytes],
signature: bytes,
verkey: bytes,
key_type: KeyType,
) -> bool:
"""Verify a signed message according to a public verification key.
Args:
message: The message(s) to verify
signature: The signature to verify
verkey: The verkey to use in verification
key_type: The key type to derive the signature verification algorithm from
Returns:
True if verified, else False
"""
# Make messages list if not already for easier checking going forward
messages = message if isinstance(message, list) else [message]
if key_type == ED25519:
if len(messages) > 1:
raise WalletError("ed25519 can only verify a single message")
return verify_signed_message_ed25519(
message=messages[0], signature=signature, verkey=verkey
)
elif key_type == BLS12381G2:
try:
return verify_signed_messages_bls12381g2(
messages=messages, signature=signature, public_key=verkey
)
except BbsException as e:
raise WalletError("Unable to verify message") from e
else:
raise WalletError(f"Unsupported key type: {key_type.key_type}")
[docs]def verify_signed_message_ed25519(
message: bytes, signature: bytes, verkey: bytes
) -> bool:
"""Verify an ed25519 signed message according to a public verification key.
Args:
message: The message to verify
signature: The signature to verify
verkey: The verkey to use in verification
Returns:
True if verified, else False
"""
try:
nacl.bindings.crypto_sign_open(signature + message, verkey)
except nacl.exceptions.BadSignatureError:
return False
return True
[docs]def add_pack_recipients(
wrapper: JweEnvelope,
cek: bytes,
to_verkeys: Sequence[bytes],
from_secret: bytes = None,
):
"""Assemble the recipients block of a packed message.
Args:
wrapper: The envelope to add recipients to
cek: The content encryption key
to_verkeys: Verkeys of recipients
from_secret: Secret to use for signing keys
Returns:
A tuple of (json result, key)
"""
for target_vk in to_verkeys:
target_pk = nacl.bindings.crypto_sign_ed25519_pk_to_curve25519(target_vk)
if from_secret:
sender_pk = sign_pk_from_sk(from_secret)
sender_vk = bytes_to_b58(sender_pk).encode("utf-8")
enc_sender = nacl.bindings.crypto_box_seal(sender_vk, target_pk)
sk = nacl.bindings.crypto_sign_ed25519_sk_to_curve25519(from_secret)
nonce = nacl.utils.random(nacl.bindings.crypto_box_NONCEBYTES)
enc_cek = nacl.bindings.crypto_box(cek, nonce, target_pk, sk)
wrapper.add_recipient(
JweRecipient(
encrypted_key=enc_cek,
header=OrderedDict(
[
("kid", bytes_to_b58(target_vk)),
("sender", b64url(enc_sender)),
("iv", b64url(nonce)),
]
),
)
)
else:
enc_sender = None
nonce = None
enc_cek = nacl.bindings.crypto_box_seal(cek, target_pk)
wrapper.add_recipient(
JweRecipient(
encrypted_key=enc_cek, header={"kid": bytes_to_b58(target_vk)}
)
)
[docs]def ed25519_pk_to_curve25519(public_key: bytes) -> bytes:
"""Covert a public Ed25519 key to a public Curve25519 key as bytes."""
return nacl.bindings.crypto_sign_ed25519_pk_to_curve25519(public_key)
[docs]def encrypt_plaintext(
message: str, add_data: bytes, key: bytes
) -> Tuple[bytes, bytes, bytes]:
"""Encrypt the payload of a packed message.
Args:
message: Message to encrypt
add_data:
key: Key used for encryption
Returns:
A tuple of (ciphertext, nonce, tag)
"""
nonce = nacl.utils.random(nacl.bindings.crypto_aead_chacha20poly1305_ietf_NPUBBYTES)
message_bin = message.encode("utf-8")
output = nacl.bindings.crypto_aead_chacha20poly1305_ietf_encrypt(
message_bin, add_data, nonce, key
)
mlen = len(message)
ciphertext = output[:mlen]
tag = output[mlen:]
return ciphertext, nonce, tag
[docs]def decrypt_plaintext(
ciphertext: bytes, recips_bin: bytes, nonce: bytes, key: bytes
) -> str:
"""Decrypt the payload of a packed message.
Args:
ciphertext:
recips_bin:
nonce:
key:
Returns:
The decrypted string
"""
output = nacl.bindings.crypto_aead_chacha20poly1305_ietf_decrypt(
ciphertext, recips_bin, nonce, key
)
return output.decode("utf-8")
[docs]def encode_pack_message(
message: str, to_verkeys: Sequence[bytes], from_secret: bytes = None
) -> bytes:
"""Assemble a packed message for a set of recipients, optionally including the sender.
Args:
message: The message to pack
to_verkeys: The verkeys to pack the message for
from_secret: The sender secret
Returns:
The encoded message
"""
wrapper = JweEnvelope(with_protected_recipients=True, with_flatten_recipients=False)
cek = nacl.bindings.crypto_secretstream_xchacha20poly1305_keygen()
add_pack_recipients(wrapper, cek, to_verkeys, from_secret)
wrapper.set_protected(
OrderedDict(
[
("enc", "xchacha20poly1305_ietf"),
("typ", "JWM/1.0"),
("alg", "Authcrypt" if from_secret else "Anoncrypt"),
]
),
)
ciphertext, nonce, tag = encrypt_plaintext(message, wrapper.protected_bytes, cek)
wrapper.set_payload(ciphertext, nonce, tag)
return wrapper.to_json().encode("utf-8")
[docs]def decode_pack_message(
enc_message: bytes, find_key: Callable
) -> Tuple[str, Optional[str], str]:
"""Decode a packed message.
Disassemble and unencrypt a packed message, returning the message content,
verification key of the sender (if available), and verification key of the
recipient.
Args:
enc_message: The encrypted message
find_key: Function to retrieve private key
Returns:
A tuple of (message, sender_vk, recip_vk)
Raises:
ValueError: If the packed message is invalid
ValueError: If the packed message recipients are invalid
ValueError: If the pack algorithm is unsupported
ValueError: If the sender's public key was not provided
"""
wrapper, recips, is_authcrypt = decode_pack_message_outer(enc_message)
payload_key, sender_vk = None, None
for recip_vk in recips:
recip_secret = find_key(recip_vk)
if recip_secret:
payload_key, sender_vk = extract_payload_key(recips[recip_vk], recip_secret)
break
if not payload_key:
raise ValueError(
"No corresponding recipient key found in {}".format(tuple(recips))
)
if not sender_vk and is_authcrypt:
raise ValueError("Sender public key not provided for Authcrypt message")
message = decode_pack_message_payload(wrapper, payload_key)
return message, sender_vk, recip_vk
[docs]def decode_pack_message_outer(enc_message: bytes) -> Tuple[dict, dict, bool]:
"""Decode the outer wrapper of a packed message and extract the recipients.
Args:
enc_message: The encrypted message
Returns: a tuple of the decoded wrapper, recipients, and authcrypt flag
"""
try:
wrapper = JweEnvelope.from_json(enc_message)
except ValidationError as err:
print(err)
raise ValueError("Invalid packed message")
alg = wrapper.protected.get("alg")
is_authcrypt = alg == "Authcrypt"
if not is_authcrypt and alg != "Anoncrypt":
raise ValueError("Unsupported pack algorithm: {}".format(alg))
recips = extract_pack_recipients(wrapper.recipients)
return wrapper, recips, is_authcrypt
[docs]def decode_pack_message_payload(wrapper: JweEnvelope, payload_key: bytes) -> str:
"""Decode the payload of a packed message once the CEK is known.
Args:
wrapper: The decoded message wrapper
payload_key: The decrypted payload key
"""
payload_bin = wrapper.ciphertext + wrapper.tag
message = decrypt_plaintext(
payload_bin, wrapper.protected_bytes, wrapper.iv, payload_key
)
return message