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
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
|
/* RSA asymmetric public-key algorithm [RFC3447]
*
* Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public Licence
* as published by the Free Software Foundation; either version
* 2 of the Licence, or (at your option) any later version.
*/
#define pr_fmt(fmt) "RSA: "fmt
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include "public_key.h"
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("RSA Public Key Algorithm");
#define kenter(FMT, ...) \
pr_devel("==> %s("FMT")\n", __func__, ##__VA_ARGS__)
#define kleave(FMT, ...) \
pr_devel("<== %s()"FMT"\n", __func__, ##__VA_ARGS__)
/*
* Hash algorithm OIDs plus ASN.1 DER wrappings [RFC4880 sec 5.2.2].
*/
static const u8 RSA_digest_info_MD5[] = {
0x30, 0x20, 0x30, 0x0C, 0x06, 0x08,
0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x02, 0x05, /* OID */
0x05, 0x00, 0x04, 0x10
};
static const u8 RSA_digest_info_SHA1[] = {
0x30, 0x21, 0x30, 0x09, 0x06, 0x05,
0x2B, 0x0E, 0x03, 0x02, 0x1A,
0x05, 0x00, 0x04, 0x14
};
static const u8 RSA_digest_info_RIPE_MD_160[] = {
0x30, 0x21, 0x30, 0x09, 0x06, 0x05,
0x2B, 0x24, 0x03, 0x02, 0x01,
0x05, 0x00, 0x04, 0x14
};
static const u8 RSA_digest_info_SHA224[] = {
0x30, 0x2d, 0x30, 0x0d, 0x06, 0x09,
0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x04,
0x05, 0x00, 0x04, 0x1C
};
static const u8 RSA_digest_info_SHA256[] = {
0x30, 0x31, 0x30, 0x0d, 0x06, 0x09,
0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01,
0x05, 0x00, 0x04, 0x20
};
static const u8 RSA_digest_info_SHA384[] = {
0x30, 0x41, 0x30, 0x0d, 0x06, 0x09,
0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x02,
0x05, 0x00, 0x04, 0x30
};
static const u8 RSA_digest_info_SHA512[] = {
0x30, 0x51, 0x30, 0x0d, 0x06, 0x09,
0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x03,
0x05, 0x00, 0x04, 0x40
};
static const struct {
const u8 *data;
size_t size;
} RSA_ASN1_templates[PKEY_HASH__LAST] = {
#define _(X) { RSA_digest_info_##X, sizeof(RSA_digest_info_##X) }
[PKEY_HASH_MD5] = _(MD5),
[PKEY_HASH_SHA1] = _(SHA1),
[PKEY_HASH_RIPE_MD_160] = _(RIPE_MD_160),
[PKEY_HASH_SHA256] = _(SHA256),
[PKEY_HASH_SHA384] = _(SHA384),
[PKEY_HASH_SHA512] = _(SHA512),
[PKEY_HASH_SHA224] = _(SHA224),
#undef _
};
/*
* RSAVP1() function [RFC3447 sec 5.2.2]
*/
static int RSAVP1(const struct public_key *key, MPI s, MPI *_m)
{
MPI m;
int ret;
/* (1) Validate 0 <= s < n */
if (mpi_cmp_ui(s, 0) < 0) {
kleave(" = -EBADMSG [s < 0]");
return -EBADMSG;
}
if (mpi_cmp(s, key->rsa.n) >= 0) {
kleave(" = -EBADMSG [s >= n]");
return -EBADMSG;
}
m = mpi_alloc(0);
if (!m)
return -ENOMEM;
/* (2) m = s^e mod n */
ret = mpi_powm(m, s, key->rsa.e, key->rsa.n);
if (ret < 0) {
mpi_free(m);
return ret;
}
*_m = m;
return 0;
}
/*
* Integer to Octet String conversion [RFC3447 sec 4.1]
*/
static int RSA_I2OSP(MPI x, size_t xLen, u8 **_X)
{
unsigned X_size, x_size;
int X_sign;
u8 *X;
/* Make sure the string is the right length. The number should begin
* with { 0x00, 0x01, ... } so we have to account for 15 leading zero
* bits not being reported by MPI.
*/
x_size = mpi_get_nbits(x);
pr_devel("size(x)=%u xLen*8=%zu\n", x_size, xLen * 8);
if (x_size != xLen * 8 - 15)
return -ERANGE;
X = mpi_get_buffer(x, &X_size, &X_sign);
if (!X)
return -ENOMEM;
if (X_sign < 0) {
kfree(X);
return -EBADMSG;
}
if (X_size != xLen - 1) {
kfree(X);
return -EBADMSG;
}
*_X = X;
return 0;
}
/*
* Perform the RSA signature verification.
* @H: Value of hash of data and metadata
* @EM: The computed signature value
* @k: The size of EM (EM[0] is an invalid location but should hold 0x00)
* @hash_size: The size of H
* @asn1_template: The DigestInfo ASN.1 template
* @asn1_size: Size of asm1_template[]
*/
static int RSA_verify(const u8 *H, const u8 *EM, size_t k, size_t hash_size,
const u8 *asn1_template, size_t asn1_size)
{
unsigned PS_end, T_offset, i;
kenter(",,%zu,%zu,%zu", k, hash_size, asn1_size);
if (k < 2 + 1 + asn1_size + hash_size)
return -EBADMSG;
/* Decode the EMSA-PKCS1-v1_5 */
if (EM[1] != 0x01) {
kleave(" = -EBADMSG [EM[1] == %02u]", EM[1]);
return -EBADMSG;
}
T_offset = k - (asn1_size + hash_size);
PS_end = T_offset - 1;
if (EM[PS_end] != 0x00) {
kleave(" = -EBADMSG [EM[T-1] == %02u]", EM[PS_end]);
return -EBADMSG;
}
for (i = 2; i < PS_end; i++) {
if (EM[i] != 0xff) {
kleave(" = -EBADMSG [EM[PS%x] == %02u]", i - 2, EM[i]);
return -EBADMSG;
}
}
if (memcmp(asn1_template, EM + T_offset, asn1_size) != 0) {
kleave(" = -EBADMSG [EM[T] ASN.1 mismatch]");
return -EBADMSG;
}
if (memcmp(H, EM + T_offset + asn1_size, hash_size) != 0) {
kleave(" = -EKEYREJECTED [EM[T] hash mismatch]");
return -EKEYREJECTED;
}
kleave(" = 0");
return 0;
}
/*
* Perform the verification step [RFC3447 sec 8.2.2].
*/
static int RSA_verify_signature(const struct public_key *key,
const struct public_key_signature *sig)
{
size_t tsize;
int ret;
/* Variables as per RFC3447 sec 8.2.2 */
const u8 *H = sig->digest;
u8 *EM = NULL;
MPI m = NULL;
size_t k;
kenter("");
if (!RSA_ASN1_templates[sig->pkey_hash_algo].data)
return -ENOTSUPP;
/* (1) Check the signature size against the public key modulus size */
k = mpi_get_nbits(key->rsa.n);
tsize = mpi_get_nbits(sig->rsa.s);
/* According to RFC 4880 sec 3.2, length of MPI is computed starting
* from most significant bit. So the RFC 3447 sec 8.2.2 size check
* must be relaxed to conform with shorter signatures - so we fail here
* only if signature length is longer than modulus size.
*/
pr_devel("step 1: k=%zu size(S)=%zu\n", k, tsize);
if (k < tsize) {
ret = -EBADMSG;
goto error;
}
/* Round up and convert to octets */
k = (k + 7) / 8;
/* (2b) Apply the RSAVP1 verification primitive to the public key */
ret = RSAVP1(key, sig->rsa.s, &m);
if (ret < 0)
goto error;
/* (2c) Convert the message representative (m) to an encoded message
* (EM) of length k octets.
*
* NOTE! The leading zero byte is suppressed by MPI, so we pass a
* pointer to the _preceding_ byte to RSA_verify()!
*/
ret = RSA_I2OSP(m, k, &EM);
if (ret < 0)
goto error;
ret = RSA_verify(H, EM - 1, k, sig->digest_size,
RSA_ASN1_templates[sig->pkey_hash_algo].data,
RSA_ASN1_templates[sig->pkey_hash_algo].size);
error:
kfree(EM);
mpi_free(m);
kleave(" = %d", ret);
return ret;
}
const struct public_key_algorithm RSA_public_key_algorithm = {
.name = "RSA",
.n_pub_mpi = 2,
.n_sec_mpi = 3,
.n_sig_mpi = 1
|