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
192
193
194
195
196
197
198
199
200
201
202
203
|
// Copyright 2024 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "components/enterprise/obfuscation/core/download_obfuscator.h"
namespace enterprise_obfuscation {
namespace {
// Calculate the overhead introduced by the obfuscation process for a given data
// source. ReadFunc is a callable type that reads a chunk of data from the
// source.
template <typename ReadFunc>
base::expected<int64_t, Error> CalculateDeobfuscationOverheadImpl(
size_t total_size,
ReadFunc read_func) {
if (total_size < kHeaderSize + kChunkSizePrefixSize) {
return RecordAndReturn<int64_t>(
base::unexpected(Error::kDeobfuscationFailed));
}
size_t offset = kHeaderSize;
int num_chunks = 0;
while (offset < total_size) {
// Read the chunk size prefix.
auto size_data_result = read_func(offset, kChunkSizePrefixSize);
if (!size_data_result.has_value()) {
return RecordAndReturn<int64_t>(
base::unexpected(Error::kDeobfuscationFailed));
}
offset += kChunkSizePrefixSize;
// Calculate the chunk size.
auto chunk_size = enterprise_obfuscation::GetObfuscatedChunkSize(
size_data_result.value());
if (!chunk_size.has_value()) {
return RecordAndReturn<int64_t>(base::unexpected(chunk_size.error()));
}
offset += chunk_size.value();
num_chunks++;
}
int64_t chunk_overhead = kAuthTagSize + kChunkSizePrefixSize;
return num_chunks * chunk_overhead + kHeaderSize;
}
} // namespace
const char DownloadObfuscationData::kUserDataKey[] =
"enterprise_obfuscation.download_obfuscation_data_key";
DownloadObfuscationData::DownloadObfuscationData(bool is_obfuscated)
: is_obfuscated(is_obfuscated) {}
DownloadObfuscationData::~DownloadObfuscationData() = default;
DownloadObfuscator::DownloadObfuscator()
: unobfuscated_hash_(
crypto::SecureHash::Create(crypto::SecureHash::SHA256)) {}
DownloadObfuscator::~DownloadObfuscator() = default;
base::expected<std::vector<uint8_t>, Error> DownloadObfuscator::ObfuscateChunk(
base::span<const uint8_t> data,
bool is_last_chunk) {
std::vector<uint8_t> result;
// Update the hash with the original data
unobfuscated_hash_->Update(data.data(), data.size());
// If it's the first chunk, create and prepend the header.
if (chunk_counter_ == 0) {
auto header = CreateHeader(&derived_key_, &nonce_prefix_);
if (!header.has_value()) {
return RecordAndReturn<std::vector<uint8_t>>(
base::unexpected(header.error()));
}
result = std::move(header.value());
}
auto obfuscated_chunk = ObfuscateDataChunk(data, derived_key_, nonce_prefix_,
chunk_counter_++, is_last_chunk);
if (!obfuscated_chunk.has_value()) {
return RecordAndReturn<std::vector<uint8_t>>(
base::unexpected(obfuscated_chunk.error()));
}
result.insert(result.end(), obfuscated_chunk->begin(),
obfuscated_chunk->end());
total_overhead_ += result.size() - data.size();
return result;
}
base::expected<base::span<const uint8_t>, Error>
DownloadObfuscator::GetNextDeobfuscatedChunk(
base::span<const uint8_t> obfuscated_data) {
if (deobfuscated_chunk_position_ == deobfuscated_chunk_.size()) {
// Deobfuscate the next chunk, as we are at the start or we've reached the
// end of the current deobfuscated chunk.
next_chunk_offset_ = 0;
auto deobfuscated_result =
DeobfuscateChunk(obfuscated_data, next_chunk_offset_);
if (!deobfuscated_result.has_value()) {
return RecordAndReturn<base::span<const uint8_t>>(
base::unexpected(deobfuscated_result.error()));
}
deobfuscated_chunk_ = std::move(deobfuscated_result.value());
deobfuscated_chunk_position_ = 0;
}
return base::span<const uint8_t>(deobfuscated_chunk_)
.subspan(deobfuscated_chunk_position_);
}
base::expected<std::vector<uint8_t>, Error>
DownloadObfuscator::DeobfuscateChunk(base::span<const uint8_t> data,
size_t& obfuscated_file_offset) {
// Check if data is unobfuscated or corrupted.
size_t per_chunk_overhead = kChunkSizePrefixSize + kAuthTagSize;
if (data.size() < per_chunk_overhead) {
return base::unexpected(Error::kDeobfuscationFailed);
}
// If it's the first chunk, get obfuscation data from header.
if (chunk_counter_ == 0) {
if (data.size() < kHeaderSize + per_chunk_overhead) {
return base::unexpected(Error::kDeobfuscationFailed);
}
auto header_data = GetHeaderData(data.first(kHeaderSize));
if (!header_data.has_value()) {
return base::unexpected(header_data.error());
}
derived_key_ = std::move(header_data->derived_key);
nonce_prefix_ = std::move(header_data->nonce_prefix);
obfuscated_file_offset = kHeaderSize;
}
// Read the size of the next chunk.
auto chunk_size = GetObfuscatedChunkSize(
data.subspan(obfuscated_file_offset, kChunkSizePrefixSize));
if (!chunk_size.has_value()) {
return base::unexpected(chunk_size.error());
}
obfuscated_file_offset += kChunkSizePrefixSize;
// Deobfuscate the next data chunk.
bool is_last_chunk =
(obfuscated_file_offset + chunk_size.value() >= data.size());
auto result = DeobfuscateDataChunk(
data.subspan(obfuscated_file_offset, chunk_size.value()), derived_key_,
nonce_prefix_, chunk_counter_++, is_last_chunk);
if (!result.has_value()) {
return base::unexpected(result.error());
}
obfuscated_file_offset += chunk_size.value();
return result.value();
}
base::expected<int64_t, Error>
DownloadObfuscator::CalculateDeobfuscationOverhead(
base::span<const uint8_t> data) {
return CalculateDeobfuscationOverheadImpl(
data.size(),
[&data](size_t offset,
size_t size) -> base::expected<base::span<const uint8_t>, Error> {
if (offset + size > data.size()) {
return RecordAndReturn<base::span<const uint8_t>>(
base::unexpected(Error::kDeobfuscationFailed));
}
return data.subspan(offset, size);
});
}
base::expected<int64_t, Error>
DownloadObfuscator::CalculateDeobfuscationOverhead(base::File& file) {
size_t file_size = file.GetLength();
std::array<char, kChunkSizePrefixSize> size_buffer;
return CalculateDeobfuscationOverheadImpl(
file_size,
[&file, &size_buffer](size_t offset, size_t size)
-> base::expected<base::span<const uint8_t>, Error> {
if (!file.Seek(base::File::FROM_BEGIN, offset)) {
return RecordAndReturn<base::span<const uint8_t>>(
base::unexpected(Error::kDeobfuscationFailed));
}
std::optional<size_t> bytes_read =
file.ReadAtCurrentPos(base::as_writable_byte_span(size_buffer));
if (!bytes_read.has_value() || *bytes_read != size) {
return RecordAndReturn<base::span<const uint8_t>>(
base::unexpected(Error::kDeobfuscationFailed));
}
return base::as_byte_span(size_buffer);
});
}
std::unique_ptr<crypto::SecureHash> DownloadObfuscator::GetUnobfuscatedHash() {
return std::move(unobfuscated_hash_);
}
void DownloadObfuscator::UpdateDeobfuscatedChunkPosition(size_t bytes_written) {
deobfuscated_chunk_position_ += bytes_written;
}
} // namespace enterprise_obfuscation
|
