1 /*
2 * Copyright (C) 2013 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #include "asn1_decoder.h"
18
19 #include <stdint.h>
20
peek_byte() const21 int asn1_context::peek_byte() const {
22 if (length_ == 0) {
23 return -1;
24 }
25 return *p_;
26 }
27
get_byte()28 int asn1_context::get_byte() {
29 if (length_ == 0) {
30 return -1;
31 }
32
33 int byte = *p_;
34 p_++;
35 length_--;
36 return byte;
37 }
38
skip_bytes(size_t num_skip)39 bool asn1_context::skip_bytes(size_t num_skip) {
40 if (length_ < num_skip) {
41 return false;
42 }
43 p_ += num_skip;
44 length_ -= num_skip;
45 return true;
46 }
47
decode_length(size_t * out_len)48 bool asn1_context::decode_length(size_t* out_len) {
49 int num_octets = get_byte();
50 if (num_octets == -1) {
51 return false;
52 }
53 if ((num_octets & 0x80) == 0x00) {
54 *out_len = num_octets;
55 return true;
56 }
57 num_octets &= kMaskTag;
58 if (static_cast<size_t>(num_octets) >= sizeof(size_t)) {
59 return false;
60 }
61 size_t length = 0;
62 for (int i = 0; i < num_octets; ++i) {
63 int byte = get_byte();
64 if (byte == -1) {
65 return false;
66 }
67 length <<= 8;
68 length += byte;
69 }
70 *out_len = length;
71 return true;
72 }
73
74 /**
75 * Returns the constructed type and advances the pointer. E.g. A0 -> 0
76 */
asn1_constructed_get()77 asn1_context* asn1_context::asn1_constructed_get() {
78 int type = get_byte();
79 if (type == -1 || (type & kMaskConstructed) != kTagConstructed) {
80 return nullptr;
81 }
82 size_t length;
83 if (!decode_length(&length) || length > length_) {
84 return nullptr;
85 }
86 asn1_context* app_ctx = new asn1_context(p_, length);
87 app_ctx->app_type_ = type & kMaskAppType;
88 return app_ctx;
89 }
90
asn1_constructed_skip_all()91 bool asn1_context::asn1_constructed_skip_all() {
92 int byte = peek_byte();
93 while (byte != -1 && (byte & kMaskConstructed) == kTagConstructed) {
94 skip_bytes(1);
95 size_t length;
96 if (!decode_length(&length) || !skip_bytes(length)) {
97 return false;
98 }
99 byte = peek_byte();
100 }
101 return byte != -1;
102 }
103
asn1_constructed_type() const104 int asn1_context::asn1_constructed_type() const {
105 return app_type_;
106 }
107
asn1_sequence_get()108 asn1_context* asn1_context::asn1_sequence_get() {
109 if ((get_byte() & kMaskTag) != kTagSequence) {
110 return nullptr;
111 }
112 size_t length;
113 if (!decode_length(&length) || length > length_) {
114 return nullptr;
115 }
116 return new asn1_context(p_, length);
117 }
118
asn1_set_get()119 asn1_context* asn1_context::asn1_set_get() {
120 if ((get_byte() & kMaskTag) != kTagSet) {
121 return nullptr;
122 }
123 size_t length;
124 if (!decode_length(&length) || length > length_) {
125 return nullptr;
126 }
127 return new asn1_context(p_, length);
128 }
129
asn1_sequence_next()130 bool asn1_context::asn1_sequence_next() {
131 size_t length;
132 if (get_byte() == -1 || !decode_length(&length) || !skip_bytes(length)) {
133 return false;
134 }
135 return true;
136 }
137
asn1_oid_get(const uint8_t ** oid,size_t * length)138 bool asn1_context::asn1_oid_get(const uint8_t** oid, size_t* length) {
139 if (get_byte() != kTagOid) {
140 return false;
141 }
142 if (!decode_length(length) || *length == 0 || *length > length_) {
143 return false;
144 }
145 *oid = p_;
146 return true;
147 }
148
asn1_octet_string_get(const uint8_t ** octet_string,size_t * length)149 bool asn1_context::asn1_octet_string_get(const uint8_t** octet_string, size_t* length) {
150 if (get_byte() != kTagOctetString) {
151 return false;
152 }
153 if (!decode_length(length) || *length == 0 || *length > length_) {
154 return false;
155 }
156 *octet_string = p_;
157 return true;
158 }
159