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Kenny Root7a4adb52013-10-09 10:14:35 -07001/*
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
Elliott Hughes26dbad22015-01-28 12:09:05 -080017#include <malloc.h>
Kenny Root7a4adb52013-10-09 10:14:35 -070018#include <stdint.h>
19#include <string.h>
20
21#include "asn1_decoder.h"
22
23
24typedef struct asn1_context {
Tao Bao76fdb242017-03-20 17:09:13 -070025 size_t length;
26 const uint8_t* p;
27 int app_type;
Kenny Root7a4adb52013-10-09 10:14:35 -070028} asn1_context_t;
29
30
31static const int kMaskConstructed = 0xE0;
32static const int kMaskTag = 0x7F;
33static const int kMaskAppType = 0x1F;
34
35static const int kTagOctetString = 0x04;
36static const int kTagOid = 0x06;
37static const int kTagSequence = 0x30;
38static const int kTagSet = 0x31;
39static const int kTagConstructed = 0xA0;
40
Tao Bao76fdb242017-03-20 17:09:13 -070041asn1_context_t* asn1_context_new(const uint8_t* buffer, size_t length) {
Kenny Root7a4adb52013-10-09 10:14:35 -070042 asn1_context_t* ctx = (asn1_context_t*) calloc(1, sizeof(asn1_context_t));
43 if (ctx == NULL) {
44 return NULL;
45 }
46 ctx->p = buffer;
47 ctx->length = length;
48 return ctx;
49}
50
51void asn1_context_free(asn1_context_t* ctx) {
52 free(ctx);
53}
54
55static inline int peek_byte(asn1_context_t* ctx) {
56 if (ctx->length <= 0) {
57 return -1;
58 }
59 return *ctx->p;
60}
61
62static inline int get_byte(asn1_context_t* ctx) {
63 if (ctx->length <= 0) {
64 return -1;
65 }
66 int byte = *ctx->p;
67 ctx->p++;
68 ctx->length--;
69 return byte;
70}
71
72static inline bool skip_bytes(asn1_context_t* ctx, size_t num_skip) {
73 if (ctx->length < num_skip) {
74 return false;
75 }
76 ctx->p += num_skip;
77 ctx->length -= num_skip;
78 return true;
79}
80
81static bool decode_length(asn1_context_t* ctx, size_t* out_len) {
82 int num_octets = get_byte(ctx);
83 if (num_octets == -1) {
84 return false;
85 }
86 if ((num_octets & 0x80) == 0x00) {
87 *out_len = num_octets;
88 return 1;
89 }
90 num_octets &= kMaskTag;
91 if ((size_t)num_octets >= sizeof(size_t)) {
92 return false;
93 }
94 size_t length = 0;
95 for (int i = 0; i < num_octets; ++i) {
96 int byte = get_byte(ctx);
97 if (byte == -1) {
98 return false;
99 }
100 length <<= 8;
101 length += byte;
102 }
103 *out_len = length;
104 return true;
105}
106
107/**
108 * Returns the constructed type and advances the pointer. E.g. A0 -> 0
109 */
110asn1_context_t* asn1_constructed_get(asn1_context_t* ctx) {
111 int type = get_byte(ctx);
112 if (type == -1 || (type & kMaskConstructed) != kTagConstructed) {
113 return NULL;
114 }
115 size_t length;
116 if (!decode_length(ctx, &length) || length > ctx->length) {
117 return NULL;
118 }
119 asn1_context_t* app_ctx = asn1_context_new(ctx->p, length);
120 app_ctx->app_type = type & kMaskAppType;
121 return app_ctx;
122}
123
124bool asn1_constructed_skip_all(asn1_context_t* ctx) {
125 int byte = peek_byte(ctx);
126 while (byte != -1 && (byte & kMaskConstructed) == kTagConstructed) {
127 skip_bytes(ctx, 1);
128 size_t length;
129 if (!decode_length(ctx, &length) || !skip_bytes(ctx, length)) {
130 return false;
131 }
132 byte = peek_byte(ctx);
133 }
134 return byte != -1;
135}
136
137int asn1_constructed_type(asn1_context_t* ctx) {
138 return ctx->app_type;
139}
140
141asn1_context_t* asn1_sequence_get(asn1_context_t* ctx) {
142 if ((get_byte(ctx) & kMaskTag) != kTagSequence) {
143 return NULL;
144 }
145 size_t length;
146 if (!decode_length(ctx, &length) || length > ctx->length) {
147 return NULL;
148 }
149 return asn1_context_new(ctx->p, length);
150}
151
152asn1_context_t* asn1_set_get(asn1_context_t* ctx) {
153 if ((get_byte(ctx) & kMaskTag) != kTagSet) {
154 return NULL;
155 }
156 size_t length;
157 if (!decode_length(ctx, &length) || length > ctx->length) {
158 return NULL;
159 }
160 return asn1_context_new(ctx->p, length);
161}
162
163bool asn1_sequence_next(asn1_context_t* ctx) {
164 size_t length;
165 if (get_byte(ctx) == -1 || !decode_length(ctx, &length) || !skip_bytes(ctx, length)) {
166 return false;
167 }
168 return true;
169}
170
Tao Bao76fdb242017-03-20 17:09:13 -0700171bool asn1_oid_get(asn1_context_t* ctx, const uint8_t** oid, size_t* length) {
Kenny Root7a4adb52013-10-09 10:14:35 -0700172 if (get_byte(ctx) != kTagOid) {
173 return false;
174 }
175 if (!decode_length(ctx, length) || *length == 0 || *length > ctx->length) {
176 return false;
177 }
178 *oid = ctx->p;
179 return true;
180}
181
Tao Bao76fdb242017-03-20 17:09:13 -0700182bool asn1_octet_string_get(asn1_context_t* ctx, const uint8_t** octet_string, size_t* length) {
Kenny Root7a4adb52013-10-09 10:14:35 -0700183 if (get_byte(ctx) != kTagOctetString) {
184 return false;
185 }
186 if (!decode_length(ctx, length) || *length == 0 || *length > ctx->length) {
187 return false;
188 }
189 *octet_string = ctx->p;
190 return true;
191}