summaryrefslogtreecommitdiffstats
path: root/asn1_decoder.cpp
blob: e7aef781c018a81b8b1adede7b8212e19db7c7e8 (plain)
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
/*
 * Copyright (C) 2013 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <malloc.h>
#include <stdint.h>
#include <string.h>

#include "asn1_decoder.h"


typedef struct asn1_context {
    size_t length;
    uint8_t* p;
    int app_type;
} asn1_context_t;


static const int kMaskConstructed = 0xE0;
static const int kMaskTag = 0x7F;
static const int kMaskAppType = 0x1F;

static const int kTagOctetString = 0x04;
static const int kTagOid = 0x06;
static const int kTagSequence = 0x30;
static const int kTagSet = 0x31;
static const int kTagConstructed = 0xA0;

asn1_context_t* asn1_context_new(uint8_t* buffer, size_t length) {
    asn1_context_t* ctx = (asn1_context_t*) calloc(1, sizeof(asn1_context_t));
    if (ctx == NULL) {
        return NULL;
    }
    ctx->p = buffer;
    ctx->length = length;
    return ctx;
}

void asn1_context_free(asn1_context_t* ctx) {
    free(ctx);
}

static inline int peek_byte(asn1_context_t* ctx) {
    if (ctx->length <= 0) {
        return -1;
    }
    return *ctx->p;
}

static inline int get_byte(asn1_context_t* ctx) {
    if (ctx->length <= 0) {
        return -1;
    }
    int byte = *ctx->p;
    ctx->p++;
    ctx->length--;
    return byte;
}

static inline bool skip_bytes(asn1_context_t* ctx, size_t num_skip) {
    if (ctx->length < num_skip) {
        return false;
    }
    ctx->p += num_skip;
    ctx->length -= num_skip;
    return true;
}

static bool decode_length(asn1_context_t* ctx, size_t* out_len) {
    int num_octets = get_byte(ctx);
    if (num_octets == -1) {
        return false;
    }
    if ((num_octets & 0x80) == 0x00) {
        *out_len = num_octets;
        return 1;
    }
    num_octets &= kMaskTag;
    if ((size_t)num_octets >= sizeof(size_t)) {
        return false;
    }
    size_t length = 0;
    for (int i = 0; i < num_octets; ++i) {
        int byte = get_byte(ctx);
        if (byte == -1) {
            return false;
        }
        length <<= 8;
        length += byte;
    }
    *out_len = length;
    return true;
}

/**
 * Returns the constructed type and advances the pointer. E.g. A0 -> 0
 */
asn1_context_t* asn1_constructed_get(asn1_context_t* ctx) {
    int type = get_byte(ctx);
    if (type == -1 || (type & kMaskConstructed) != kTagConstructed) {
        return NULL;
    }
    size_t length;
    if (!decode_length(ctx, &length) || length > ctx->length) {
        return NULL;
    }
    asn1_context_t* app_ctx = asn1_context_new(ctx->p, length);
    app_ctx->app_type = type & kMaskAppType;
    return app_ctx;
}

bool asn1_constructed_skip_all(asn1_context_t* ctx) {
    int byte = peek_byte(ctx);
    while (byte != -1 && (byte & kMaskConstructed) == kTagConstructed) {
        skip_bytes(ctx, 1);
        size_t length;
        if (!decode_length(ctx, &length) || !skip_bytes(ctx, length)) {
            return false;
        }
        byte = peek_byte(ctx);
    }
    return byte != -1;
}

int asn1_constructed_type(asn1_context_t* ctx) {
    return ctx->app_type;
}

asn1_context_t* asn1_sequence_get(asn1_context_t* ctx) {
    if ((get_byte(ctx) & kMaskTag) != kTagSequence) {
        return NULL;
    }
    size_t length;
    if (!decode_length(ctx, &length) || length > ctx->length) {
        return NULL;
    }
    return asn1_context_new(ctx->p, length);
}

asn1_context_t* asn1_set_get(asn1_context_t* ctx) {
    if ((get_byte(ctx) & kMaskTag) != kTagSet) {
        return NULL;
    }
    size_t length;
    if (!decode_length(ctx, &length) || length > ctx->length) {
        return NULL;
    }
    return asn1_context_new(ctx->p, length);
}

bool asn1_sequence_next(asn1_context_t* ctx) {
    size_t length;
    if (get_byte(ctx) == -1 || !decode_length(ctx, &length) || !skip_bytes(ctx, length)) {
        return false;
    }
    return true;
}

bool asn1_oid_get(asn1_context_t* ctx, uint8_t** oid, size_t* length) {
    if (get_byte(ctx) != kTagOid) {
        return false;
    }
    if (!decode_length(ctx, length) || *length == 0 || *length > ctx->length) {
        return false;
    }
    *oid = ctx->p;
    return true;
}

bool asn1_octet_string_get(asn1_context_t* ctx, uint8_t** octet_string, size_t* length) {
    if (get_byte(ctx) != kTagOctetString) {
        return false;
    }
    if (!decode_length(ctx, length) || *length == 0 || *length > ctx->length) {
        return false;
    }
    *octet_string = ctx->p;
    return true;
}