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
|
/*
* asn1.c
* ------
* Minimal ASN.1 implementation in support of Cryptech libhal.
*
* The functions in this module are not intended to be part of the
* public API. Rather, these are utility functions used by more than
* one module within the library, which would otherwise have to be
* duplicated. The main reason for keeping these private is to avoid
* having the public API depend on any details of the underlying
* bignum implementation (currently libtfm, but that might change).
*
* As of this writing, the ASN.1 support we need is quite minimal, so,
* rather than attempting to clean all the unecessary cruft out of a
* general purpose ASN.1 implementation, we hand code the very small
* number of data types we need. At some point this will probably
* become impractical, at which point we might want to look into using
* something like the asn1c compiler.
*
* Authors: Rob Austein
* Copyright (c) 2015, SUNET
*
* 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 OWNER 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.
*/
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <stddef.h>
#include <string.h>
#include <assert.h>
#include "hal.h"
#include "asn1_internal.h"
/*
* Encode tag and length fields of an ASN.1 object. If der is NULL,
* just return the size that would be encoded.
*/
hal_error_t hal_asn1_encode_header(const uint8_t tag,
const size_t value_len,
uint8_t *der, size_t *der_len, const size_t der_max)
{
size_t header_len = 2; /* Shortest encoding is one octet each for tag and length */
if (value_len >= 128) /* Add octets for longer length encoding as needed */
for (size_t n = value_len; n > 0; n >>= 8)
++header_len;
if (der_len != NULL)
*der_len = header_len;
if (der == NULL) /* If caller just wanted the length, we're done */
return HAL_OK;
/*
* Make sure there's enough room for header + value, then encode.
*/
if (value_len + header_len > der_max)
return HAL_ERROR_RESULT_TOO_LONG;
*der++ = tag;
if (value_len < 128) {
*der = (uint8_t) value_len;
}
else {
*der = 0x80 | (uint8_t) (header_len -= 2);
for (size_t n = value_len; n > 0 && header_len > 0; n >>= 8)
der[header_len--] = (uint8_t) (n & 0xFF);
}
return HAL_OK;
}
/*
* Encode an unsigned ASN.1 INTEGER from a libtfm bignum. If der is
* NULL, just return the length of what we would have encoded.
*/
hal_error_t hal_asn1_encode_integer(const fp_int * const bn,
uint8_t *der, size_t *der_len, const size_t der_max)
{
if (bn == NULL)
return HAL_ERROR_BAD_ARGUMENTS;
/*
* We only handle unsigned INTEGERs, so we need to pad data with a
* leading zero if the most significant bit is set, to avoid
* flipping the ASN.1 sign bit. Conveniently, this also handles the
* difference between libtfm's and ASN.1's encoding of zero.
*/
if (fp_cmp_d(unconst_fp_int(bn), 0) == FP_LT)
return HAL_ERROR_BAD_ARGUMENTS;
const int leading_zero = fp_iszero(bn) || (fp_count_bits(unconst_fp_int(bn)) & 7) == 0;
const size_t vlen = fp_unsigned_bin_size(unconst_fp_int(bn)) + leading_zero;
hal_error_t err;
size_t hlen;
if ((err = hal_asn1_encode_header(ASN1_INTEGER, vlen, der, &hlen, der_max)) != HAL_OK)
return err;
if (der_len != NULL)
*der_len = hlen + vlen;
if (der == NULL)
return HAL_OK;
if (hlen + vlen > der_max)
return HAL_ERROR_RESULT_TOO_LONG;
der += hlen;
if (leading_zero)
*der++ = 0x00;
fp_to_unsigned_bin(unconst_fp_int(bn), der);
return HAL_OK;
}
/*
* Parse tag and length of an ASN.1 object. Tag must match value
* specified by the caller. On success, sets hlen and vlen to lengths
* of header and value, respectively.
*/
hal_error_t hal_asn1_decode_header(const uint8_t tag,
const uint8_t * const der, size_t der_max,
size_t *hlen, size_t *vlen)
{
assert(der != NULL && hlen != NULL && vlen != NULL);
if (der_max < 2 || der[0] != tag)
return HAL_ERROR_ASN1_PARSE_FAILED;
if ((der[1] & 0x80) == 0) {
*hlen = 2;
*vlen = der[1];
}
else {
*hlen = 2 + (der[1] & 0x7F);
*vlen = 0;
if (*hlen > der_max)
return HAL_ERROR_ASN1_PARSE_FAILED;
for (size_t i = 2; i < *hlen; i++)
*vlen = (*vlen << 8) + der[i];
}
if (*hlen + *vlen > der_max)
return HAL_ERROR_ASN1_PARSE_FAILED;
return HAL_OK;
}
/*
* Decode an ASN.1 INTEGER into a libtfm bignum. Since we only
* support (or need to support, or expect to see) unsigned integers,
* we return failure if the sign bit is set in the ASN.1 INTEGER.
*/
hal_error_t hal_asn1_decode_integer(fp_int *bn,
const uint8_t * const der, size_t *der_len, const size_t der_max)
{
if (bn == NULL || der == NULL)
return HAL_ERROR_BAD_ARGUMENTS;
hal_error_t err;
size_t hlen, vlen;
if ((err = hal_asn1_decode_header(ASN1_INTEGER, der, der_max, &hlen, &vlen)) != HAL_OK)
return err;
if (der_len != NULL)
*der_len = hlen + vlen;
if (vlen < 1 || (der[hlen] & 0x80) != 0x00)
return HAL_ERROR_ASN1_PARSE_FAILED;
fp_init(bn);
fp_read_unsigned_bin(bn, (uint8_t *) der + hlen, vlen);
return HAL_OK;
}
/*
* Local variables:
* indent-tabs-mode: nil
* End:
*/
|
