mirror of https://github.com/nucypher/pyUmbral.git
Allows passing callable KDFs to key wrapping methods. Default is Scrypt
David Núñez
parent
bce37b790a
commit
317469767d
umbral
125
umbral/keys.py
125
umbral/keys.py
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@ -24,7 +24,7 @@ from cryptography.hazmat.backends import default_backend
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from cryptography.hazmat.backends.openssl.ec import _EllipticCurvePrivateKey, _EllipticCurvePublicKey
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from cryptography.hazmat.primitives import hashes
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from cryptography.hazmat.primitives.kdf.hkdf import HKDF
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from cryptography.hazmat.primitives.kdf.scrypt import Scrypt
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from cryptography.hazmat.primitives.kdf.scrypt import Scrypt as CryptographyScrypt
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from nacl.secret import SecretBox
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from umbral import openssl
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@ -35,61 +35,74 @@ from umbral.point import Point
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from umbral.curve import Curve
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from umbral.random_oracles import hash_to_curvebn
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__DEFAULT_SCRIPT_COST = 20
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__SALT_SIZE = 32
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def _derive_key_from_password(password: bytes, salt: bytes,
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_scrypt_cost: int = __DEFAULT_SCRIPT_COST) -> bytes:
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class Scrypt:
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__DEFAULT_SCRYPT_COST = 20
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def __call__(self,
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password: bytes,
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salt: bytes,
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**kwargs) -> bytes:
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"""
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Derives a symmetric encryption key from a pair of password and salt.
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It also accepts an additional _scrypt_cost argument.
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WARNING: RFC7914 recommends that you use a 2^20 cost value for sensitive
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files. It is NOT recommended to change the `_scrypt_cost` value unless
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you know what you are doing.
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:param password: byte-encoded password used to derive a symmetric key
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:param salt: cryptographic salt added during key derivation
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:return:
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"""
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_scrypt_cost = kwargs.get('_scrypt_cost', Scrypt.__DEFAULT_SCRYPT_COST)
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derived_key = CryptographyScrypt(
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salt=salt,
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length=SecretBox.KEY_SIZE,
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n=2 ** _scrypt_cost,
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r=8,
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p=1,
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backend=default_backend()
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).derive(password)
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return derived_key
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def derive_key_from_password(password: bytes,
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salt: bytes,
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**kwargs) -> bytes:
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"""
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Derives a symmetric encryption key from a pair of password and salt.
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WARNING: RFC7914 recommends that you use a 2^20 cost value for sensitive
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files. It is NOT recommended to change the `_scrypt_cost` value unless
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you know what you are doing.
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:param password: byte-encoded password used to derive a symmetric key
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:param salt: cryptographic salt added during key derivation
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:param _scrypt_cost:
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:return:
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It uses Scrypt by default.
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"""
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derived_key = Scrypt(
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salt=salt,
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length=SecretBox.KEY_SIZE,
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n=2 ** _scrypt_cost,
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r=8,
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p=1,
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backend=default_backend()
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).derive(password)
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kdf = kwargs.get('kdf', Scrypt)()
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derived_key = kdf(password, salt, **kwargs)
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return derived_key
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def wrap_key(key_to_wrap: bytes,
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wrapping_key: Optional[bytes] = None,
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password: Optional[bytes] = None,
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_scrypt_cost: int = __DEFAULT_SCRIPT_COST,
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) -> bytes:
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**kwargs) -> bytes:
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"""
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Wraps a key using a provided wrapping key. Alternatively, it can derive
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the wrapping key from a password.
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WARNING: RFC7914 recommends that you use a 2^20 cost value for sensitive
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files. It is NOT recommended to change the `_scrypt_cost` value unless
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you know what you are doing.
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:param key_to_wrap:
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:param wrapping_key:
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:param password:
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:param _scrypt_cost:
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:return:
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"""
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if all((password, wrapping_key)) or not any((password, wrapping_key)):
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raise ValueError("Either password or wrapping_key must be passed")
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wrapped_key = b''
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if password:
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salt = os.urandom(__SALT_SIZE)
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wrapping_key = _derive_key_from_password(password=password,
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salt=salt,
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_scrypt_cost=_scrypt_cost)
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wrapping_key = derive_key_from_password(password=password,
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salt=salt,
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**kwargs)
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wrapped_key = salt
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elif wrapping_key:
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wrapped_key = b''
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wrapped_key += SecretBox(wrapping_key).encrypt(key_to_wrap)
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return wrapped_key
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@ -98,18 +111,13 @@ def wrap_key(key_to_wrap: bytes,
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def unwrap_key(wrapped_key: bytes,
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wrapping_key: Optional[bytes] = None,
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password: Optional[bytes] = None,
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_scrypt_cost: int = __DEFAULT_SCRIPT_COST,
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) -> bytes:
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**kwargs) -> bytes:
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"""
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Unwraps a key using a provided wrapping key. Alternatively, it can derive
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the wrapping key from a password.
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WARNING: RFC7914 recommends that you use a 2^20 cost value for sensitive
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files. It is NOT recommended to change the `_scrypt_cost` value unless
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you know what you are doing.
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:param wrapped_key:
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:param wrapping_key:
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:param password:
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:param _scrypt_cost:
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:return:
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"""
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if all((password, wrapping_key)) or not any((password, wrapping_key)):
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@ -118,15 +126,15 @@ def unwrap_key(wrapped_key: bytes,
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if password:
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salt = wrapped_key[:__SALT_SIZE]
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wrapped_key = wrapped_key[__SALT_SIZE:]
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wrapping_key = _derive_key_from_password(password=password,
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salt=salt,
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_scrypt_cost=_scrypt_cost)
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wrapping_key = derive_key_from_password(password=password,
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salt=salt,
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**kwargs)
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key = SecretBox(wrapping_key).decrypt(wrapped_key)
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return key
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class UmbralPrivateKey():
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class UmbralPrivateKey:
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def __init__(self, bn_key: CurveBN, params: UmbralParameters) -> None:
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"""
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Initializes an Umbral private key.
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@ -151,9 +159,9 @@ class UmbralPrivateKey():
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key_bytes: bytes,
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wrapping_key: Optional[bytes] = None,
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password: Optional[bytes] = None,
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_scrypt_cost: int = 20,
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params: Optional[UmbralParameters] = None,
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decoder: Optional[Callable] = None) -> 'UmbralPrivateKey':
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decoder: Optional[Callable] = None,
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**kwargs) -> 'UmbralPrivateKey':
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"""
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Loads an Umbral private key from bytes.
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Optionally, allows a decoder function to be passed as a param to decode
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@ -161,10 +169,6 @@ class UmbralPrivateKey():
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Optionally, uses a wrapping key to unwrap an encrypted Umbral private key.
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Alternatively, if a password is provided it will derive the wrapping key
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from it.
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WARNING: RFC7914 recommends that you use a 2^20 cost value for sensitive
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files. Unless you changed this when you called `to_bytes`, you should
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not change it here. It is NOT recommended to change the `_scrypt_cost`
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value unless you know what you're doing.
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"""
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if params is None:
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params = default_params()
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@ -176,7 +180,7 @@ class UmbralPrivateKey():
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key_bytes = unwrap_key(wrapped_key=key_bytes,
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wrapping_key=wrapping_key,
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password=password,
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_scrypt_cost=_scrypt_cost)
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**kwargs)
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bn_key = CurveBN.from_bytes(key_bytes, params.curve)
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return cls(bn_key, params)
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@ -184,9 +188,8 @@ class UmbralPrivateKey():
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def to_bytes(self,
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wrapping_key: Optional[bytes] = None,
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password: Optional[bytes] = None,
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_scrypt_cost: int = 20,
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encoder: Optional[Callable] = None,
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) -> bytes:
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**kwargs) -> bytes:
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"""
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Returns an UmbralPrivateKey as bytes with optional symmetric
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encryption via nacl's Salsa20-Poly1305.
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@ -194,9 +197,6 @@ class UmbralPrivateKey():
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Scrypt for key derivation.
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Optionally, allows an encoder to be passed in as a param to encode the
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data before returning it.
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WARNING: RFC7914 recommends that you use a 2^20 cost value for sensitive
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files. It is NOT recommended to change the `_scrypt_cost` value unless
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you know what you are doing.
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"""
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key_bytes = self.bn_key.to_bytes()
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@ -205,7 +205,7 @@ class UmbralPrivateKey():
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key_bytes = wrap_key(key_to_wrap=key_bytes,
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wrapping_key=wrapping_key,
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password=password,
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_scrypt_cost=_scrypt_cost)
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**kwargs)
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if encoder:
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key_bytes = encoder(key_bytes)
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@ -403,8 +403,8 @@ class UmbralKeyingMaterial:
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key_bytes: bytes,
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wrapping_key: Optional[bytes] = None,
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password: Optional[bytes] = None,
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_scrypt_cost: int = 20,
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decoder: Optional[Callable] = None) -> 'UmbralKeyingMaterial':
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decoder: Optional[Callable] = None,
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**kwargs) -> 'UmbralKeyingMaterial':
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"""
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Loads an UmbralKeyingMaterial from bytes.
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Optionally, allows a decoder function to be passed as a param to decode
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@ -412,10 +412,6 @@ class UmbralKeyingMaterial:
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Optionally, uses a wrapping key to unwrap an encrypted UmbralKeyingMaterial.
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Alternatively, if a password is provided it will derive the wrapping key
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from it.
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WARNING: RFC7914 recommends that you use a 2^20 cost value for sensitive
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files. Unless you changed this when you called `to_bytes`, you should
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not change it here. It is NOT recommended to change the `_scrypt_cost`
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value unless you know what you're doing.
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"""
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if decoder:
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key_bytes = decoder(key_bytes)
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@ -424,15 +420,15 @@ class UmbralKeyingMaterial:
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key_bytes = unwrap_key(wrapped_key=key_bytes,
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wrapping_key=wrapping_key,
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password=password,
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_scrypt_cost=_scrypt_cost)
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**kwargs)
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return cls(keying_material=key_bytes)
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def to_bytes(self,
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wrapping_key: Optional[bytes] = None,
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password: Optional[bytes] = None,
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_scrypt_cost: int = 20,
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encoder: Optional[Callable] = None) -> bytes:
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encoder: Optional[Callable] = None,
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**kwargs) -> bytes:
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"""
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Returns an UmbralKeyingMaterial as bytes with optional symmetric
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encryption via nacl's Salsa20-Poly1305.
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@ -440,9 +436,6 @@ class UmbralKeyingMaterial:
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Scrypt for key derivation.
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Optionally, allows an encoder to be passed in as a param to encode the
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data before returning it.
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WARNING: RFC7914 recommends that you use a 2^20 cost value for sensitive
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files. It is NOT recommended to change the `_scrypt_cost` value unless
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you know what you are doing.
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"""
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key_bytes = self.__keying_material
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@ -451,7 +444,7 @@ class UmbralKeyingMaterial:
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key_bytes = wrap_key(key_to_wrap=key_bytes,
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wrapping_key=wrapping_key,
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password=password,
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_scrypt_cost=_scrypt_cost)
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**kwargs)
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if encoder:
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key_bytes = encoder(key_bytes)
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