1"""
2X25519 key management
3"""
4
5# SPDX-License-Identifier: Apache-2.0
6
7from cryptography.hazmat.backends import default_backend
8from cryptography.hazmat.primitives import serialization
9from cryptography.hazmat.primitives.asymmetric import x25519
10
11from .general import KeyClass
12from .privatebytes import PrivateBytesMixin
13
14
15class X25519UsageError(Exception):
16    pass
17
18
19class X25519Public(KeyClass):
20    def __init__(self, key):
21        self.key = key
22
23    def shortname(self):
24        return "x25519"
25
26    def _unsupported(self, name):
27        raise X25519UsageError("Operation {} requires private key".format(name))
28
29    def _get_public(self):
30        return self.key
31
32    def get_public_bytes(self):
33        # The key is embedded into MBUboot in "SubjectPublicKeyInfo" format
34        return self._get_public().public_bytes(
35                encoding=serialization.Encoding.DER,
36                format=serialization.PublicFormat.SubjectPublicKeyInfo)
37
38    def get_public_pem(self):
39        return self._get_public().public_bytes(
40                encoding=serialization.Encoding.PEM,
41                format=serialization.PublicFormat.SubjectPublicKeyInfo)
42
43    def get_private_bytes(self, minimal, format):
44        self._unsupported('get_private_bytes')
45
46    def export_private(self, path, passwd=None):
47        self._unsupported('export_private')
48
49    def export_public(self, path):
50        """Write the public key to the given file."""
51        pem = self._get_public().public_bytes(
52                encoding=serialization.Encoding.PEM,
53                format=serialization.PublicFormat.SubjectPublicKeyInfo)
54        with open(path, 'wb') as f:
55            f.write(pem)
56
57    def sig_type(self):
58        return "X25519"
59
60    def sig_tlv(self):
61        return "X25519"
62
63    def sig_len(self):
64        return 32
65
66
67class X25519(X25519Public, PrivateBytesMixin):
68    """
69    Wrapper around an X25519 private key.
70    """
71
72    def __init__(self, key):
73        """key should be an instance of EllipticCurvePrivateKey"""
74        self.key = key
75
76    @staticmethod
77    def generate():
78        pk = x25519.X25519PrivateKey.generate()
79        return X25519(pk)
80
81    def _get_public(self):
82        return self.key.public_key()
83
84    _VALID_FORMATS = {
85        'pkcs8': serialization.PrivateFormat.PKCS8
86    }
87    _DEFAULT_FORMAT = 'pkcs8'
88
89    def get_private_bytes(self, minimal, format):
90        _, priv = self._get_private_bytes(minimal, format,
91                                          X25519UsageError)
92        return priv
93
94    def export_private(self, path, passwd=None):
95        """
96        Write the private key to the given file, protecting it with the
97        optional password.
98        """
99        if passwd is None:
100            enc = serialization.NoEncryption()
101        else:
102            enc = serialization.BestAvailableEncryption(passwd)
103        pem = self.key.private_bytes(
104                encoding=serialization.Encoding.PEM,
105                format=serialization.PrivateFormat.PKCS8,
106                encryption_algorithm=enc)
107        with open(path, 'wb') as f:
108            f.write(pem)
109
110    def sign_digest(self, digest):
111        """Return the actual signature"""
112        return self.key.sign(data=digest)
113
114    def verify_digest(self, signature, digest):
115        """Verify that signature is valid for given digest"""
116        k = self.key
117        if isinstance(self.key, x25519.X25519PrivateKey):
118            k = self.key.public_key()
119        return k.verify(signature=signature, data=digest)
120