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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