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
|
# ===================================================================
#
# Copyright (c) 2014, Legrandin <helderijs@gmail.com>
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
#
# 1. Redistributions of source code must retain the above copyright
# notice, this list of conditions and the following disclaimer.
# 2. Redistributions in binary form must reproduce the above copyright
# notice, this list of conditions and the following disclaimer in
# the documentation and/or other materials provided with the
# distribution.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
# FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
# COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
# BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
# ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
# POSSIBILITY OF SUCH DAMAGE.
# ===================================================================
import Cryptodome.Util.number
from Cryptodome.Util.number import ceil_div, bytes_to_long, long_to_bytes
from Cryptodome.Util.asn1 import DerSequence, DerNull, DerOctetString, DerObjectId
class PKCS115_SigScheme:
"""A signature object for ``RSASSA-PKCS1-v1_5``.
Do not instantiate directly.
Use :func:`Cryptodome.Signature.pkcs1_15.new`.
"""
def __init__(self, rsa_key):
"""Initialize this PKCS#1 v1.5 signature scheme object.
:Parameters:
rsa_key : an RSA key object
Creation of signatures is only possible if this is a *private*
RSA key. Verification of signatures is always possible.
"""
self._key = rsa_key
def can_sign(self):
"""Return ``True`` if this object can be used to sign messages."""
return self._key.has_private()
def sign(self, msg_hash):
"""Create the PKCS#1 v1.5 signature of a message.
This function is also called ``RSASSA-PKCS1-V1_5-SIGN`` and
it is specified in
`section 8.2.1 of RFC8017 <https://tools.ietf.org/html/rfc8017#page-36>`_.
:parameter msg_hash:
This is an object from the :mod:`Cryptodome.Hash` package.
It has been used to digest the message to sign.
:type msg_hash: hash object
:return: the signature encoded as a *byte string*.
:raise ValueError: if the RSA key is not long enough for the given hash algorithm.
:raise TypeError: if the RSA key has no private half.
"""
# See 8.2.1 in RFC3447
modBits = Cryptodome.Util.number.size(self._key.n)
k = ceil_div(modBits,8) # Convert from bits to bytes
# Step 1
em = _EMSA_PKCS1_V1_5_ENCODE(msg_hash, k)
# Step 2a (OS2IP)
em_int = bytes_to_long(em)
# Step 2b (RSASP1)
m_int = self._key._decrypt(em_int)
# Step 2c (I2OSP)
signature = long_to_bytes(m_int, k)
return signature
def verify(self, msg_hash, signature):
"""Check if the PKCS#1 v1.5 signature over a message is valid.
This function is also called ``RSASSA-PKCS1-V1_5-VERIFY`` and
it is specified in
`section 8.2.2 of RFC8037 <https://tools.ietf.org/html/rfc8017#page-37>`_.
:parameter msg_hash:
The hash that was carried out over the message. This is an object
belonging to the :mod:`Cryptodome.Hash` module.
:type parameter: hash object
:parameter signature:
The signature that needs to be validated.
:type signature: byte string
:raise ValueError: if the signature is not valid.
"""
# See 8.2.2 in RFC3447
modBits = Cryptodome.Util.number.size(self._key.n)
k = ceil_div(modBits, 8) # Convert from bits to bytes
# Step 1
if len(signature) != k:
raise ValueError("Invalid signature")
# Step 2a (O2SIP)
signature_int = bytes_to_long(signature)
# Step 2b (RSAVP1)
em_int = self._key._encrypt(signature_int)
# Step 2c (I2OSP)
em1 = long_to_bytes(em_int, k)
# Step 3
try:
possible_em1 = [ _EMSA_PKCS1_V1_5_ENCODE(msg_hash, k, True) ]
# MD2/4/5 hashes always require NULL params in AlgorithmIdentifier.
# For all others, it is optional.
try:
algorithm_is_md = msg_hash.oid.startswith('1.2.840.113549.2.')
except AttributeError:
algorithm_is_md = False
if not algorithm_is_md: # MD2/MD4/MD5
possible_em1.append(_EMSA_PKCS1_V1_5_ENCODE(msg_hash, k, False))
except ValueError:
raise ValueError("Invalid signature")
# Step 4
# By comparing the full encodings (as opposed to checking each
# of its components one at a time) we avoid attacks to the padding
# scheme like Bleichenbacher's (see http://www.mail-archive.com/cryptography@metzdowd.com/msg06537).
#
if em1 not in possible_em1:
raise ValueError("Invalid signature")
pass
def _EMSA_PKCS1_V1_5_ENCODE(msg_hash, emLen, with_hash_parameters=True):
"""
Implement the ``EMSA-PKCS1-V1_5-ENCODE`` function, as defined
in PKCS#1 v2.1 (RFC3447, 9.2).
``_EMSA-PKCS1-V1_5-ENCODE`` actually accepts the message ``M`` as input,
and hash it internally. Here, we expect that the message has already
been hashed instead.
:Parameters:
msg_hash : hash object
The hash object that holds the digest of the message being signed.
emLen : int
The length the final encoding must have, in bytes.
with_hash_parameters : bool
If True (default), include NULL parameters for the hash
algorithm in the ``digestAlgorithm`` SEQUENCE.
:attention: the early standard (RFC2313) stated that ``DigestInfo``
had to be BER-encoded. This means that old signatures
might have length tags in indefinite form, which
is not supported in DER. Such encoding cannot be
reproduced by this function.
:Return: An ``emLen`` byte long string that encodes the hash.
"""
# First, build the ASN.1 DER object DigestInfo:
#
# DigestInfo ::= SEQUENCE {
# digestAlgorithm AlgorithmIdentifier,
# digest OCTET STRING
# }
#
# where digestAlgorithm identifies the hash function and shall be an
# algorithm ID with an OID in the set PKCS1-v1-5DigestAlgorithms.
#
# PKCS1-v1-5DigestAlgorithms ALGORITHM-IDENTIFIER ::= {
# { OID id-md2 PARAMETERS NULL }|
# { OID id-md5 PARAMETERS NULL }|
# { OID id-sha1 PARAMETERS NULL }|
# { OID id-sha256 PARAMETERS NULL }|
# { OID id-sha384 PARAMETERS NULL }|
# { OID id-sha512 PARAMETERS NULL }
# }
#
# Appendix B.1 also says that for SHA-1/-2 algorithms, the parameters
# should be omitted. They may be present, but when they are, they shall
# have NULL value.
digestAlgo = DerSequence([ DerObjectId(msg_hash.oid).encode() ])
if with_hash_parameters:
digestAlgo.append(DerNull().encode())
digest = DerOctetString(msg_hash.digest())
digestInfo = DerSequence([
digestAlgo.encode(),
digest.encode()
]).encode()
# We need at least 11 bytes for the remaining data: 3 fixed bytes and
# at least 8 bytes of padding).
if emLen<len(digestInfo)+11:
raise TypeError("Selected hash algorith has a too long digest (%d bytes)." % len(digest))
PS = b'\xFF' * (emLen - len(digestInfo) - 3)
return b'\x00\x01' + PS + b'\x00' + digestInfo
def new(rsa_key):
"""Create a signature object for creating
or verifying PKCS#1 v1.5 signatures.
:parameter rsa_key:
The RSA key to use for signing or verifying the message.
This is a :class:`Cryptodome.PublicKey.RSA` object.
Signing is only possible when ``rsa_key`` is a **private** RSA key.
:type rsa_key: RSA object
:return: a :class:`PKCS115_SigScheme` signature object
"""
return PKCS115_SigScheme(rsa_key)
|