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"""
X25519 key management
"""
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import serialization
from cryptography.hazmat.primitives.asymmetric import x25519
from .general import KeyClass
class X25519UsageError(Exception):
pass
class X25519Public(KeyClass):
def __init__(self, key):
self.key = key
def shortname(self):
return "x25519"
def _unsupported(self, name):
raise X25519UsageError("Operation {} requires private key".format(name))
def _get_public(self):
return self.key
def get_public_bytes(self):
# The key is embedded into MBUboot in "SubjectPublicKeyInfo" format
return self._get_public().public_bytes(
encoding=serialization.Encoding.DER,
format=serialization.PublicFormat.SubjectPublicKeyInfo)
def get_private_bytes(self, minimal):
self._unsupported('get_private_bytes')
def export_private(self, path, passwd=None):
self._unsupported('export_private')
def export_public(self, path):
"""Write the public key to the given file."""
pem = self._get_public().public_bytes(
encoding=serialization.Encoding.PEM,
format=serialization.PublicFormat.SubjectPublicKeyInfo)
with open(path, 'wb') as f:
f.write(pem)
def sig_type(self):
return "X25519"
def sig_tlv(self):
return "X25519"
def sig_len(self):
return 32
class X25519(X25519Public):
"""
Wrapper around an X25519 private key.
"""
def __init__(self, key):
"""key should be an instance of EllipticCurvePrivateKey"""
self.key = key
@staticmethod
def generate():
pk = x25519.X25519PrivateKey.generate()
return X25519(pk)
def _get_public(self):
return self.key.public_key()
def get_private_bytes(self, minimal):
return self.key.private_bytes(
encoding=serialization.Encoding.DER,
format=serialization.PrivateFormat.PKCS8,
encryption_algorithm=serialization.NoEncryption())
def export_private(self, path, passwd=None):
"""
Write the private key to the given file, protecting it with the
optional password.
"""
if passwd is None:
enc = serialization.NoEncryption()
else:
enc = serialization.BestAvailableEncryption(passwd)
pem = self.key.private_bytes(
encoding=serialization.Encoding.PEM,
format=serialization.PrivateFormat.PKCS8,
encryption_algorithm=enc)
with open(path, 'wb') as f:
f.write(pem)
def sign_digest(self, digest):
"""Return the actual signature"""
return self.key.sign(data=digest)
def verify_digest(self, signature, digest):
"""Verify that signature is valid for given digest"""
k = self.key
if isinstance(self.key, x25519.X25519PrivateKey):
k = self.key.public_key()
return k.verify(signature=signature, data=digest)
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