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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;
}
(*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;
} // 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++) = COUNTER_TAG;
pos = varint_encode(pos, counter);
*(pos++) = RATCHET_KEY_TAG;
pos = varint_encode(pos, ratchet_key_length);
writer.ratchet_key = pos;
pos += ratchet_key_length;
*(pos++) = CIPHERTEXT_TAG;
pos = varint_encode(pos, ciphertext_length);
writer.ciphertext = pos;
pos += ciphertext_length;
}
std::size_t 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 flags = 0;
std::size_t result = std::size_t(-1);
if (pos == end) return result;
reader.version = *(pos++);
while (pos != end) {
uint8_t tag = *(pos);
if (tag == COUNTER_TAG) {
++pos;
std::uint8_t const * counter_start = pos;
pos = varint_skip(pos, end);
reader.counter = varint_decode<std::uint32_t>(counter_start, pos);
flags |= 1;
} else if (tag == RATCHET_KEY_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 result;
reader.ratchet_key_length = len;
reader.ratchet_key = pos;
pos += len;
flags |= 2;
} else if (tag == CIPHERTEXT_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 result;
reader.ciphertext_length = len;
reader.ciphertext = pos;
pos += len;
flags |= 4;
} else if (tag & 0x7 == 0) {
pos = varint_skip(pos, end);
pos = varint_skip(pos, end);
} else if (tag & 0x7 == 2) {
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 result;
pos += len;
} else {
return std::size_t(-1);
}
}
if (flags == 0x7) {
reader.input = input;
reader.input_length = input_length;
return std::size_t(pos - input);
}
return result;
}
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