Commit ba446e7a authored by Mark Haines's avatar Mark Haines
Browse files

Add a message encoder/decoder

parent 8df4d9e9
#include <cstddef>
#include <cstdint>
namespace axolotl {
/**
* The length of the buffer needed to hold a message.
*/
std::size_t encode_message_length(
std::uint32_t counter,
std::size_t ratchet_key_length,
std::size_t ciphertext_length,
std::size_t mac_length
);
struct MessageWriter {
std::size_t body_length;
std::uint8_t * ratchet_key;
std::uint8_t * ciphertext;
std::uint8_t * mac;
};
struct MessageReader {
std::size_t body_length;
std::uint8_t version;
std::uint32_t counter;
std::size_t ratchet_key_length;
std::size_t ciphertext_length;
std::size_t mac_length;
std::uint8_t const * ratchet_key;
std::uint8_t const * ciphertext;
std::uint8_t const * mac;
};
/**
* Writes the message headers into the output buffer.
* Returns a writer struct populated with pointers into the output buffer.
*/
MessageWriter encode_message(
std::uint8_t version,
std::uint32_t counter,
std::size_t ratchet_key_length,
std::size_t ciphertext_length,
std::uint8_t * output
);
/**
* Reads the message headers from the input buffer.
* Returns a reader struct populated with pointers into the input buffer.
* On failure the returned body_length will be 0.
*/
MessageReader decode_message(
std::uint8_t const * input, std::size_t input_length,
std::size_t mac_length
);
} // namespace axolotl
#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);
return length + mac_length;
}
axolotl::MessageWriter axolotl::encode_message(
std::uint8_t version,
std::uint32_t counter,
std::size_t ratchet_key_length,
std::size_t ciphertext_length,
std::uint8_t * output
) {
axolotl::MessageWriter result;
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);
result.ratchet_key = pos;
pos += ratchet_key_length;
*(pos++) = CIPHERTEXT_TAG;
pos = varint_encode(pos, ciphertext_length);
result.ciphertext = pos;
pos += ciphertext_length;
result.body_length = pos - output;
result.mac = pos;
return result;
}
axolotl::MessageReader axolotl::decode_message(
std::uint8_t const * input, std::size_t input_length,
std::size_t mac_length
) {
axolotl::MessageReader result;
result.body_length = 0;
std::uint8_t const * pos = input;
std::uint8_t const * end = input + input_length - mac_length;
std::uint8_t flags = 0;
result.mac = end;
result.mac_length = mac_length;
if (pos == end) return result;
result.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);
result.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;
result.ratchet_key_length = len;
result.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;
result.ciphertext_length = len;
result.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 result;
}
}
if (flags == 0x7) {
result.body_length = end - input;
}
return result;
}
#include "axolotl/message.hh"
#include "unittest.hh"
int main() {
std::uint8_t message1[36] = "\x03\n\nratchetkey\x10\x01\"\nciphertexthmacsha2";
std::uint8_t message2[36] = "\x03\x10\x01\n\nratchetkey\"\nciphertexthmacsha2";
std::uint8_t ratchetkey[11] = "ratchetkey";
std::uint8_t ciphertext[11] = "ciphertext";
std::uint8_t hmacsha2[9] = "hmacsha2";
{ /* Message decode test */
TestCase test_case("Message decode test");
axolotl::MessageReader reader(axolotl::decode_message(message1, 35, 8));
assert_equals(std::size_t(27), reader.body_length);
assert_equals(std::uint8_t(3), reader.version);
assert_equals(std::uint32_t(1), reader.counter);
assert_equals(std::size_t(10), reader.ratchet_key_length);
assert_equals(std::size_t(10), reader.ciphertext_length);
assert_equals(std::size_t(8), reader.mac_length);
assert_equals(ratchetkey, reader.ratchet_key, 10);
assert_equals(ciphertext, reader.ciphertext, 10);
assert_equals(hmacsha2, reader.mac, 8);
} /* Message decode test */
{ /* Message encode test */
TestCase test_case("Message encode test");
std::size_t length = axolotl::encode_message_length(1, 10, 10, 8);
assert_equals(std::size_t(35), length);
std::uint8_t output[length];
axolotl::MessageWriter writer(axolotl::encode_message(3, 1, 10, 10, output));
assert_equals(std::size_t(27), writer.body_length);
std::memcpy(writer.ratchet_key, ratchetkey, 10);
std::memcpy(writer.ciphertext, ciphertext, 10);
std::memcpy(writer.mac, hmacsha2, 8);
assert_equals(message2, output, 35);
} /* Message encode test */
}
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