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/* Copyright 2015 OpenMarket Ltd
*
* 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 "axolotl/message.hh"
namespace {
template<typename T>
std::size_t varint_length(
T value
) {
std::size_t result = 1;
while (value >= 128U) {
++result;
value >>= 7;
}
return result;
}
template<typename T>
std::uint8_t * varint_encode(
std::uint8_t * output,
T value
) {
while (value >= 128U) {
*(output++) = (0x7F & value) | 0x80;
value >>= 7;
}
(*output++) = value;
return output;
}
template<typename T>
T varint_decode(
std::uint8_t const * varint_start,
std::uint8_t const * varint_end
) {
T value = 0;
do {
value <<= 7;
value |= 0x7F & *(--varint_end);
} while (varint_end != varint_start);
return value;
}
std::uint8_t const * varint_skip(
std::uint8_t const * input,
std::uint8_t const * input_end
) {
while (input != input_end) {
std::uint8_t tmp = *(input++);
if ((tmp & 0x80) == 0) {
return input;
}
}
return input;
}
std::size_t varstring_length(
std::size_t string_length
) {
return varint_length(string_length) + string_length;
}
static std::size_t const VERSION_LENGTH = 1;
static std::uint8_t const RATCHET_KEY_TAG = 012;
static std::uint8_t const COUNTER_TAG = 020;
static std::uint8_t const CIPHERTEXT_TAG = 042;
std::uint8_t * encode(
std::uint8_t * pos,
std::uint8_t tag,
std::uint32_t value
) {
*(pos++) = tag;
return varint_encode(pos, value);
}
std::uint8_t * encode(
std::uint8_t * pos,
std::uint8_t tag,
std::uint8_t * & value, std::size_t value_length
) {
*(pos++) = tag;
pos = varint_encode(pos, value_length);
value = pos;
return pos + value_length;
}
std::uint8_t const * decode(
std::uint8_t const * pos, std::uint8_t const * end,
std::uint8_t tag,
std::uint32_t & value, bool & has_value
) {
if (pos != end && *pos == tag) {
++pos;
std::uint8_t const * value_start = pos;
pos = varint_skip(pos, end);
value = varint_decode<std::uint32_t>(value_start, pos);
has_value = true;
}
return pos;
}
std::uint8_t const * decode(
std::uint8_t const * pos, std::uint8_t const * end,
std::uint8_t tag,
std::uint8_t const * & value, std::size_t & value_length
) {
if (pos != end && *pos == tag) {
++pos;
std::uint8_t const * len_start = pos;
pos = varint_skip(pos, end);
std::size_t len = varint_decode<std::size_t>(len_start, pos);
if (len > end - pos) return end;
value = pos;
value_length = len;
pos += len;
}
return pos;
}
std::uint8_t const * skip_unknown(
std::uint8_t const * pos, std::uint8_t const * end
) {
if (pos != end) {
uint8_t tag = *pos;
if ((tag & 0x7) == 0) {
pos = varint_skip(pos, end);
pos = varint_skip(pos, end);
} else if ((tag & 0x7) == 2) {
pos = varint_skip(pos, end);
std::uint8_t const * len_start = pos;
pos = varint_skip(pos, end);
std::size_t len = varint_decode<std::size_t>(len_start, pos);
if (len > end - pos) return end;
pos += len;
} else {
return end;
}
}
return pos;
}
} // namespace
std::size_t axolotl::encode_message_length(
std::uint32_t counter,
std::size_t ratchet_key_length,
std::size_t ciphertext_length,
std::size_t mac_length
) {
std::size_t length = VERSION_LENGTH;
length += 1 + varstring_length(ratchet_key_length);
length += 1 + varint_length(counter);
length += 1 + varstring_length(ciphertext_length);
length += mac_length;
return length;
}
void axolotl::encode_message(
axolotl::MessageWriter & writer,
std::uint8_t version,
std::uint32_t counter,
std::size_t ratchet_key_length,
std::size_t ciphertext_length,
std::uint8_t * output
) {
std::uint8_t * pos = output;
*(pos++) = version;
pos = encode(pos, RATCHET_KEY_TAG, writer.ratchet_key, ratchet_key_length);
pos = encode(pos, COUNTER_TAG, counter);
pos = encode(pos, CIPHERTEXT_TAG, writer.ciphertext, ciphertext_length);
}
void axolotl::decode_message(
axolotl::MessageReader & reader,
std::uint8_t const * input, std::size_t input_length,
std::size_t mac_length
) {
std::uint8_t const * pos = input;
std::uint8_t const * end = input + input_length - mac_length;
std::uint8_t const * unknown = nullptr;
if (pos == end) return;
reader.version = *(pos++);
reader.input = input;
reader.input_length = input_length;
reader.has_counter = false;
reader.ratchet_key = nullptr;
reader.ciphertext = nullptr;
while (pos != end) {
pos = decode(
pos, end, RATCHET_KEY_TAG,
reader.ratchet_key, reader.ratchet_key_length
);
pos = decode(
pos, end, COUNTER_TAG,
reader.counter, reader.has_counter
);
pos = decode(
pos, end, CIPHERTEXT_TAG,
reader.ciphertext, reader.ciphertext_length
);
if (unknown == pos) {
pos = skip_unknown(pos, end);
}
unknown = pos;
}
}
namespace {
static std::uint8_t const ONE_TIME_KEY_ID_TAG = 010;
static std::uint8_t const BASE_KEY_TAG = 022;
static std::uint8_t const IDENTITY_KEY_TAG = 032;
static std::uint8_t const MESSAGE_TAG = 042;
} // namespace
std::size_t axolotl::encode_one_time_key_message_length(
std::uint32_t one_time_key_id,
std::size_t identity_key_length,
std::size_t base_key_length,
std::size_t message_length
) {
std::size_t length = VERSION_LENGTH;
length += 1 + varint_length(one_time_key_id);
length += 1 + varstring_length(identity_key_length);
length += 1 + varstring_length(base_key_length);
length += 1 + varstring_length(message_length);
return length;
}
void axolotl::encode_one_time_key_message(
axolotl::PreKeyMessageWriter & writer,
std::uint8_t version,
std::uint32_t one_time_key_id,
std::size_t identity_key_length,
std::size_t base_key_length,
std::size_t message_length,
std::uint8_t * output
) {
std::uint8_t * pos = output;
*(pos++) = version;
pos = encode(pos, ONE_TIME_KEY_ID_TAG, one_time_key_id);
pos = encode(pos, BASE_KEY_TAG, writer.base_key, base_key_length);
pos = encode(pos, IDENTITY_KEY_TAG, writer.identity_key, identity_key_length);
pos = encode(pos, MESSAGE_TAG, writer.message, message_length);
}
void axolotl::decode_one_time_key_message(
PreKeyMessageReader & reader,
std::uint8_t const * input, std::size_t input_length
) {
std::uint8_t const * pos = input;
std::uint8_t const * end = input + input_length;
std::uint8_t const * unknown = nullptr;
if (pos == end) return;
reader.version = *(pos++);
reader.has_one_time_key_id = false;
reader.identity_key = nullptr;
reader.base_key = nullptr;
reader.message = nullptr;
while (pos != end) {
pos = decode(
pos, end, ONE_TIME_KEY_ID_TAG,
reader.one_time_key_id, reader.has_one_time_key_id
);
pos = decode(
pos, end, BASE_KEY_TAG,
reader.base_key, reader.base_key_length
);
pos = decode(
pos, end, IDENTITY_KEY_TAG,
reader.identity_key, reader.identity_key_length
);
pos = decode(
pos, end, MESSAGE_TAG,
reader.message, reader.message_length
);
if (unknown == pos) {
pos = skip_unknown(pos, end);
}
unknown = pos;
}
}
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