1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
|
"""
<Module Name>
eddsa.py
<Author>
Lukas Puehringer <lukas.puehringer@nyu.edu>
<Started>
Oct 22, 2019
<Copyright>
See LICENSE for licensing information.
<Purpose>
EdDSA/ed25519 algorithm-specific handling routines for pubkey and signature
parsing and verification.
"""
import binascii
from securesystemslib import exceptions
from securesystemslib._gpg import util as gpg_util
from securesystemslib._gpg.exceptions import PacketParsingError
CRYPTO = True
NO_CRYPTO_MSG = "EdDSA key support for GPG requires the cryptography library"
try:
from cryptography.exceptions import InvalidSignature
from cryptography.hazmat.primitives.asymmetric import (
ed25519 as pyca_ed25519,
)
except ImportError:
CRYPTO = False
# ECC Curve OID (see RFC4880-bis8 9.2.)
ED25519_PUBLIC_KEY_OID = bytearray.fromhex("2B 06 01 04 01 DA 47 0F 01")
# EdDSA Point Format (see RFC4880-bis8 13.3.)
ED25519_PUBLIC_KEY_LENGTH = 33
ED25519_PUBLIC_KEY_PREFIX = 0x40
# EdDSA signature byte length (see RFC 8032 5.1.6. (6))
ED25519_SIG_LENGTH = 64
def get_pubkey_params(data):
"""
<Purpose>
Parse algorithm-specific part for EdDSA public keys
See RFC4880-bis8 sections 5.6.5. Algorithm-Specific Part for EdDSA Keys,
9.2. ECC Curve OID and 13.3. EdDSA Point Format for more details.
<Arguments>
data:
The EdDSA public key data AFTER the one-octet number denoting the
public-key algorithm of this key.
<Exceptions>
securesystemslib._gpg.exceptions.PacketParsingError or IndexError:
if the public key data is malformed.
<Side Effects>
None.
<Returns>
A dictionary with an element "q" that holds the ascii hex representation
of the MPI of an EC point representing an EdDSA public key.
"""
ptr = 0
curve_oid_len = data[ptr]
ptr += 1
curve_oid = data[ptr : ptr + curve_oid_len]
ptr += curve_oid_len
# See 9.2. ECC Curve OID
if curve_oid != ED25519_PUBLIC_KEY_OID:
raise PacketParsingError(
f"bad ed25519 curve OID '{curve_oid}', expected {ED25519_PUBLIC_KEY_OID}'"
)
# See 13.3. EdDSA Point Format
public_key_len = gpg_util.get_mpi_length(data[ptr : ptr + 2])
ptr += 2
if public_key_len != ED25519_PUBLIC_KEY_LENGTH:
raise PacketParsingError(
f"bad ed25519 MPI length '{public_key_len}', "
f"expected {ED25519_PUBLIC_KEY_LENGTH}'"
)
public_key_prefix = data[ptr]
ptr += 1
if public_key_prefix != ED25519_PUBLIC_KEY_PREFIX:
raise PacketParsingError(
f"bad ed25519 MPI prefix '{public_key_prefix}', "
f"expected '{ED25519_PUBLIC_KEY_PREFIX}'"
)
public_key = data[ptr : ptr + public_key_len - 1]
return {"q": binascii.hexlify(public_key).decode("ascii")}
def get_signature_params(data):
"""
<Purpose>
Parse algorithm-specific fields for EdDSA signatures.
See RFC4880-bis8 section 5.2.3. Version 4 and 5 Signature Packet Formats
for more details.
<Arguments>
data:
The EdDSA signature data AFTER the two-octet field holding the
left 16 bits of the signed hash value.
<Exceptions>
IndexError if the signature data is malformed.
<Side Effects>
None.
<Returns>
The concatenation of the parsed MPI R and S values of the EdDSA signature,
i.e. ENC(R) || ENC(S) (see RFC8032 3.4 Verify).
"""
ptr = 0
r_length = gpg_util.get_mpi_length(data[ptr : ptr + 2])
ptr += 2
r = data[ptr : ptr + r_length]
ptr += r_length
s_length = gpg_util.get_mpi_length(data[ptr : ptr + 2])
ptr += 2
s = data[ptr : ptr + s_length]
# Left-zero-pad 'r' and 's' values that are shorter than required by RFC 8032
# (5.1.6.), to make up for omitted leading zeros in RFC 4880 (3.2.) MPIs.
# This is especially important for 's', which is little-endian.
r = r.rjust(ED25519_SIG_LENGTH // 2, b"\x00")
s = s.rjust(ED25519_SIG_LENGTH // 2, b"\x00")
return r + s
def create_pubkey(pubkey_info):
"""
<Purpose>
Create and return an Ed25519PublicKey object from the passed pubkey_info
using pyca/cryptography.
<Arguments>
pubkey_info:
The ED25519 public key dict.
<Exceptions>
securesystemslib.exceptions.UnsupportedLibraryError if
the cryptography module is unavailable
<Returns>
A cryptography.hazmat.primitives.asymmetric.ed25519.Ed25519PublicKey based
on the passed pubkey_info.
"""
if not CRYPTO: # pragma: no cover
raise exceptions.UnsupportedLibraryError(NO_CRYPTO_MSG)
public_bytes = binascii.unhexlify(pubkey_info["keyval"]["public"]["q"])
public_key = pyca_ed25519.Ed25519PublicKey.from_public_bytes(public_bytes)
return public_key
def verify_signature(signature_object, pubkey_info, content, hash_algorithm_id):
"""
<Purpose>
Verify the passed signature against the passed content with the passed
ED25519 public key using pyca/cryptography.
<Arguments>
signature_object:
A signature dict.
pubkey_info:
A DSA public key dict.
hash_algorithm_id:
one of SHA1, SHA256, SHA512 (see securesystemslib._gpg.constants)
used to verify the signature
NOTE: Overrides any hash algorithm specification in "pubkey_info"'s
"hashes" or "method" fields.
content:
The signed bytes against which the signature is verified
<Exceptions>
securesystemslib.exceptions.UnsupportedLibraryError if:
the cryptography module is unavailable
ValueError:
if the passed hash_algorithm_id is not supported (see
securesystemslib._gpg.util.get_hashing_class)
<Returns>
True if signature verification passes and False otherwise.
"""
if not CRYPTO: # pragma: no cover
raise exceptions.UnsupportedLibraryError(NO_CRYPTO_MSG)
hasher = gpg_util.get_hashing_class(hash_algorithm_id)
pubkey_object = create_pubkey(pubkey_info)
# See RFC4880-bis8 14.8. EdDSA and 5.2.4 "Computing Signatures"
digest = gpg_util.hash_object(
binascii.unhexlify(signature_object["other_headers"]), hasher(), content
)
try:
pubkey_object.verify(binascii.unhexlify(signature_object["signature"]), digest)
return True
except InvalidSignature:
return False
|
