From ba446e7a125381d8d992fba2011f16f7f6e2806a Mon Sep 17 00:00:00 2001
From: Mark Haines <mjark@negativecurvature.net>
Date: Wed, 25 Feb 2015 11:20:12 +0000
Subject: [PATCH] Add a message encoder/decoder
---
include/axolotl/message.hh | 63 ++++++++++++++
src/message.cpp | 171 +++++++++++++++++++++++++++++++++++++
tests/test_message.cpp | 53 ++++++++++++
3 files changed, 287 insertions(+)
create mode 100644 include/axolotl/message.hh
create mode 100644 src/message.cpp
create mode 100644 tests/test_message.cpp
diff --git a/include/axolotl/message.hh b/include/axolotl/message.hh
new file mode 100644
index 0000000..85579cf
--- /dev/null
+++ b/include/axolotl/message.hh
@@ -0,0 +1,63 @@
+#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
diff --git a/src/message.cpp b/src/message.cpp
new file mode 100644
index 0000000..d0e45e0
--- /dev/null
+++ b/src/message.cpp
@@ -0,0 +1,171 @@
+#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;
+}
diff --git a/tests/test_message.cpp b/tests/test_message.cpp
new file mode 100644
index 0000000..a09d7e7
--- /dev/null
+++ b/tests/test_message.cpp
@@ -0,0 +1,53 @@
+#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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