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/*
* 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;
const 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(const 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, const 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, const 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;
}
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