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Use internal implementation for X25519 key exchanges
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RNS/Cryptography/Curve25519.py
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148
RNS/Cryptography/Curve25519.py
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"""A pure Python implementation of Curve25519
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This module supports both a low-level interface through curve25519(base_point, secret)
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and curve25519_base(secret) that take 32-byte blocks of data as inputs and a higher
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level interface using the X25519PrivateKey and X25519PublicKey classes that are
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compatible with the classes in cryptography.hazmat.primitives.asymmetric.x25519 with
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the same names.
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"""
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# By Nicko van Someren, 2021. This code is released into the public domain.
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# #### WARNING ####
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# Since this code makes use of Python's built-in large integer types, it is NOT EXPECTED
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# to run in constant time. While some effort is made to minimise the time variations,
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# the underlying math functions are likely to have running times that are highly
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# value-dependent, leaving this code potentially vulnerable to timing attacks. If this
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# code is to be used to provide cryptographic security in an environment where the start
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# and end times of the execution can be guessed, inferred or measured then it is critical
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# that steps are taken to hide the execution time, for instance by adding a delay so that
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# encrypted packets are not sent until a fixed time after the _start_ of execution.
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# Implements ladder multiplication as described in "Montgomery curves and the Montgomery
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# ladder" by Daniel J. Bernstein and Tanja Lange. https://eprint.iacr.org/2017/293.pdf
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# Curve25519 is a Montgomery curve defined by:
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# y**2 = x**3 + A * x**2 + x mod P
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# where P = 2**255-19 and A = 486662
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import os
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P = 2 ** 255 - 19
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_A = 486662
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def _point_add(point_n, point_m, point_diff):
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"""Given the projection of two points and their difference, return their sum"""
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(xn, zn) = point_n
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(xm, zm) = point_m
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(x_diff, z_diff) = point_diff
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x = (z_diff << 2) * (xm * xn - zm * zn) ** 2
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z = (x_diff << 2) * (xm * zn - zm * xn) ** 2
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return x % P, z % P
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def _point_double(point_n):
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"""Double a point provided in projective coordinates"""
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(xn, zn) = point_n
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xn2 = xn ** 2
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zn2 = zn ** 2
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x = (xn2 - zn2) ** 2
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xzn = xn * zn
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z = 4 * xzn * (xn2 + _A * xzn + zn2)
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return x % P, z % P
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def _const_time_swap(a, b, swap):
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"""Swap two values in constant time"""
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index = int(swap) * 2
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temp = (a, b, b, a)
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return temp[index:index+2]
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def _raw_curve25519(base, n):
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"""Raise the point base to the power n"""
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zero = (1, 0)
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one = (base, 1)
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mP, m1P = zero, one
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for i in reversed(range(256)):
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bit = bool(n & (1 << i))
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mP, m1P = _const_time_swap(mP, m1P, bit)
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mP, m1P = _point_double(mP), _point_add(mP, m1P, one)
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mP, m1P = _const_time_swap(mP, m1P, bit)
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x, z = mP
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inv_z = pow(z, P - 2, P)
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return (x * inv_z) % P
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def _unpack_number(s):
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"""Unpack 32 bytes to a 256 bit value"""
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if len(s) != 32:
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raise ValueError('Curve25519 values must be 32 bytes')
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return int.from_bytes(s, "little")
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def _pack_number(n):
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"""Pack a value into 32 bytes"""
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return n.to_bytes(32, "little")
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def _fix_secret(n):
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"""Mask a value to be an acceptable exponent"""
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n &= ~7
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n &= ~(128 << 8 * 31)
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n |= 64 << 8 * 31
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return n
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def curve25519(base_point_raw, secret_raw):
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"""Raise the base point to a given power"""
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base_point = _unpack_number(base_point_raw)
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secret = _fix_secret(_unpack_number(secret_raw))
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return _pack_number(_raw_curve25519(base_point, secret))
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def curve25519_base(secret_raw):
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"""Raise the generator point to a given power"""
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secret = _fix_secret(_unpack_number(secret_raw))
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return _pack_number(_raw_curve25519(9, secret))
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class X25519PublicKey:
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def __init__(self, x):
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self.x = x
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@classmethod
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def from_public_bytes(cls, data):
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return cls(_unpack_number(data))
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def public_bytes(self):
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return _pack_number(self.x)
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class X25519PrivateKey:
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def __init__(self, a):
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self.a = a
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@classmethod
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def generate(cls):
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return cls.from_private_bytes(os.urandom(32))
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@classmethod
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def from_private_bytes(cls, data):
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return cls(_fix_secret(_unpack_number(data)))
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def private_bytes(self):
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return _pack_number(self.a)
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def public_key(self):
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return X25519PublicKey.from_public_bytes(_pack_number(_raw_curve25519(9, self.a)))
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def exchange(self, peer_public_key):
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if isinstance(peer_public_key, bytes):
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peer_public_key = X25519PublicKey.from_public_bytes(peer_public_key)
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return _pack_number(_raw_curve25519(peer_public_key.x, self.a))
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10
RNS/Cryptography/__init__.py
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10
RNS/Cryptography/__init__.py
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import os
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import glob
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from .Hashes import sha256
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from .HKDF import hkdf
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from .PKCS7 import PKCS7
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from .Fernet import Fernet
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modules = glob.glob(os.path.dirname(__file__)+"/*.py")
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__all__ = [ os.path.basename(f)[:-3] for f in modules if not f.endswith('__init__.py')]
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@ -28,11 +28,10 @@ import atexit
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import hashlib
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from .vendor import umsgpack as umsgpack
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from cryptography.hazmat.backends import default_backend
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from cryptography.hazmat.primitives import serialization
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from cryptography.hazmat.primitives.asymmetric.ed25519 import Ed25519PrivateKey, Ed25519PublicKey
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from cryptography.hazmat.primitives.asymmetric.x25519 import X25519PrivateKey, X25519PublicKey
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from RNS.Cryptography.Curve25519 import X25519PrivateKey, X25519PublicKey
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from RNS.Cryptography import Fernet
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@ -292,11 +291,7 @@ class Identity:
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def create_keys(self):
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self.prv = X25519PrivateKey.generate()
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self.prv_bytes = self.prv.private_bytes(
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encoding=serialization.Encoding.Raw,
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format=serialization.PrivateFormat.Raw,
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encryption_algorithm=serialization.NoEncryption()
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)
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self.prv_bytes = self.prv.private_bytes()
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self.sig_prv = Ed25519PrivateKey.generate()
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self.sig_prv_bytes = self.sig_prv.private_bytes(
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@ -306,10 +301,7 @@ class Identity:
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)
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self.pub = self.prv.public_key()
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self.pub_bytes = self.pub.public_bytes(
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encoding=serialization.Encoding.Raw,
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format=serialization.PublicFormat.Raw
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)
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self.pub_bytes = self.pub.public_bytes()
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self.sig_pub = self.sig_prv.public_key()
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self.sig_pub_bytes = self.sig_pub.public_bytes(
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@ -347,10 +339,7 @@ class Identity:
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self.sig_prv = Ed25519PrivateKey.from_private_bytes(self.sig_prv_bytes)
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self.pub = self.prv.public_key()
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self.pub_bytes = self.pub.public_bytes(
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encoding=serialization.Encoding.Raw,
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format=serialization.PublicFormat.Raw
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)
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self.pub_bytes = self.pub.public_bytes()
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self.sig_pub = self.sig_prv.public_key()
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self.sig_pub_bytes = self.sig_pub.public_bytes(
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@ -416,10 +405,7 @@ class Identity:
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"""
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if self.pub != None:
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ephemeral_key = X25519PrivateKey.generate()
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ephemeral_pub_bytes = ephemeral_key.public_key().public_bytes(
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encoding=serialization.Encoding.Raw,
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format=serialization.PublicFormat.Raw
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)
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ephemeral_pub_bytes = ephemeral_key.public_key().public_bytes()
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shared_key = ephemeral_key.exchange(self.pub)
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# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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# SOFTWARE.
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from cryptography.hazmat.backends import default_backend
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from cryptography.hazmat.primitives import hashes
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from cryptography.hazmat.primitives import serialization
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from cryptography.hazmat.primitives.asymmetric.ed25519 import Ed25519PrivateKey, Ed25519PublicKey
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from cryptography.hazmat.primitives.asymmetric.x25519 import X25519PrivateKey, X25519PublicKey
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from RNS.Cryptography.Curve25519 import X25519PrivateKey, X25519PublicKey
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from RNS.Cryptography import Fernet
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from time import sleep
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@ -178,10 +177,7 @@ class Link:
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self.fernet = None
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self.pub = self.prv.public_key()
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self.pub_bytes = self.pub.public_bytes(
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encoding=serialization.Encoding.Raw,
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format=serialization.PublicFormat.Raw
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)
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self.pub_bytes = self.pub.public_bytes()
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self.sig_pub = self.sig_prv.public_key()
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self.sig_pub_bytes = self.sig_pub.public_bytes(
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