From 6ecea67718803e96e00a18f97ae8abc83ecaa1c2 Mon Sep 17 00:00:00 2001 From: Mark Haines Date: Fri, 12 Jun 2015 14:09:41 +0100 Subject: Implement the session key exchange --- src/session.cpp | 319 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 319 insertions(+) create mode 100644 src/session.cpp (limited to 'src/session.cpp') diff --git a/src/session.cpp b/src/session.cpp new file mode 100644 index 0000000..be2bce7 --- /dev/null +++ b/src/session.cpp @@ -0,0 +1,319 @@ +#include "axolotl/session.hh" +#include "axolotl/cipher.hh" +#include "axolotl/crypto.hh" +#include "axolotl/account.hh" +#include "axolotl/memory.hh" +#include "axolotl/message.hh" + +#include + +namespace { + +static const std::size_t KEY_LENGTH = 32; +static const std::uint8_t PROTOCOL_VERSION = 0x3; + +static const std::uint8_t ROOT_KDF_INFO[] = "AXOLOTL_ROOT"; +static const std::uint8_t RATCHET_KDF_INFO[] = "AXOLOTL_RATCHET"; +static const std::uint8_t CIPHER_KDF_INFO[] = "AXOLOTL_KEYS"; + +static const axolotl::CipherAesSha256 AXOLOTL_CIPHER( + CIPHER_KDF_INFO, sizeof(CIPHER_KDF_INFO) -1 +); + +static const axolotl::KdfInfo AXOLOTL_KDF_INFO = { + ROOT_KDF_INFO, sizeof(ROOT_KDF_INFO) - 1, + RATCHET_KDF_INFO, sizeof(RATCHET_KDF_INFO) - 1 +}; + +} // namespace + +axolotl::Session::Session( +) : ratchet(AXOLOTL_KDF_INFO, AXOLOTL_CIPHER), + last_error(axolotl::ErrorCode::SUCCESS), + received_message(false), + bob_one_time_key_id(0) { + +} + + +std::size_t axolotl::Session::new_outbound_session_random_length() { + return KEY_LENGTH; +} + + +std::size_t axolotl::Session::new_outbound_session( + axolotl::Account const & local_account, + axolotl::Curve25519PublicKey const & identity_key, + axolotl::RemoteKey const & one_time_key, + std::uint8_t const * random, std::size_t random_length +) { + if (random_length < new_outbound_session_random_length()) { + last_error = axolotl::ErrorCode::NOT_ENOUGH_RANDOM; + return std::size_t(-1); + } + + Curve25519KeyPair base_key; + axolotl::generate_key(random, base_key); + + received_message = false; + alice_identity_key.id = local_account.identity_key.id; + alice_identity_key.key = local_account.identity_key.key; + alice_base_key = base_key; + bob_one_time_key_id = one_time_key.id; + + std::uint8_t shared_secret[160]; + std::memset(shared_secret, 0xFF, 32); + + axolotl::curve25519_shared_secret( + ); + axolotl::curve25519_shared_secret( + base_key, identity_key, shared_secret + 64 + ); + axolotl::curve25519_shared_secret( + ); + axolotl::curve25519_shared_secret( + base_key, one_time_key.key, shared_secret + 128 + ); + + axolotl::unset(base_key); + axolotl::unset(shared_secret); + + return std::size_t(0); +} + +namespace { + +bool check_message_fields( + axolotl::PreKeyMessageReader & reader +) { + bool ok = true; + ok = ok && reader.identity_key; + ok = ok && reader.identity_key_length == KEY_LENGTH; + ok = ok && reader.message; + ok = ok && reader.base_key; + ok = ok && reader.base_key_length == KEY_LENGTH; + ok = ok && reader.has_one_time_key_id; + ok = ok && reader.has_registration_id; + return ok; +} + +} // namespace + + +std::size_t axolotl::Session::new_inbound_session( + axolotl::Account & local_account, + std::uint8_t const * one_time_key_message, std::size_t message_length +) { + axolotl::PreKeyMessageReader reader; + decode_one_time_key_message(reader, one_time_key_message, message_length); + + if (!check_message_fields(reader)) { + last_error = axolotl::ErrorCode::BAD_MESSAGE_FORMAT; + return std::size_t(-1); + } + + alice_identity_key.id = reader.registration_id; + std::memcpy(alice_identity_key.key.public_key, reader.identity_key, 32); + std::memcpy(alice_base_key.public_key, reader.base_key, 32); + bob_one_time_key_id = reader.one_time_key_id; + + + axolotl::LocalKey const * bob_one_time_key = local_account.lookup_key( + bob_one_time_key_id + ); + + last_error = axolotl::ErrorCode::BAD_MESSAGE_KEY_ID; + return std::size_t(-1); + } + + std::uint8_t shared_secret[160]; + std::memset(shared_secret, 0xFF, 32); + + axolotl::curve25519_shared_secret( + ); + axolotl::curve25519_shared_secret( + local_account.identity_key.key, alice_base_key, shared_secret + 64 + ); + axolotl::curve25519_shared_secret( + ); + axolotl::curve25519_shared_secret( + bob_one_time_key->key, alice_base_key, shared_secret + 128 + ); + + + return std::size_t(0); +} + + +bool axolotl::Session::matches_inbound_session( + std::uint8_t const * one_time_key_message, std::size_t message_length +) { + axolotl::PreKeyMessageReader reader; + decode_one_time_key_message(reader, one_time_key_message, message_length); + + if (!check_message_fields(reader)) { + return false; + } + + bool same = true; + same = same && 0 == std::memcmp( + reader.identity_key, alice_identity_key.key.public_key, KEY_LENGTH + ); + same = same && 0 == std::memcmp( + reader.base_key, alice_base_key.public_key, KEY_LENGTH + ); + same = same && reader.one_time_key_id == bob_one_time_key_id; + same = same && reader.registration_id == alice_identity_key.id; + return same; +} + + +axolotl::MessageType axolotl::Session::encrypt_message_type() { + if (received_message) { + return axolotl::MessageType::MESSAGE; + } else { + return axolotl::MessageType::PRE_KEY_MESSAGE; + } +} + + +std::size_t axolotl::Session::encrypt_message_length( + std::size_t plaintext_length +) { + std::size_t message_length = ratchet.encrypt_output_length( + plaintext_length + ); + + if (received_message) { + return message_length; + } + + return encode_one_time_key_message_length( + alice_identity_key.id, + bob_one_time_key_id, + KEY_LENGTH, + KEY_LENGTH, + message_length + ); +} + + +std::size_t axolotl::Session::encrypt_random_length() { + return ratchet.encrypt_random_length(); +} + + +std::size_t axolotl::Session::encrypt( + std::uint8_t const * plaintext, std::size_t plaintext_length, + std::uint8_t const * random, std::size_t random_length, + std::uint8_t * message, std::size_t message_length +) { + if (message_length < encrypt_message_length(plaintext_length)) { + last_error = axolotl::ErrorCode::OUTPUT_BUFFER_TOO_SMALL; + return std::size_t(-1); + } + std::uint8_t * message_body; + std::size_t message_body_length = ratchet.encrypt_output_length( + plaintext_length + ); + + if (received_message) { + message_body = message; + } else { + axolotl::PreKeyMessageWriter writer; + encode_one_time_key_message( + writer, + PROTOCOL_VERSION, + alice_identity_key.id, + bob_one_time_key_id, + KEY_LENGTH, + KEY_LENGTH, + message_body_length, + message + ); + std::memcpy( + writer.identity_key, alice_identity_key.key.public_key, KEY_LENGTH + ); + std::memcpy( + writer.base_key, alice_base_key.public_key, KEY_LENGTH + ); + message_body = writer.message; + } + + std::size_t result = ratchet.encrypt( + plaintext, plaintext_length, + random, random_length, + message_body, message_body_length + ); + + if (result == std::size_t(-1)) { + last_error = ratchet.last_error; + ratchet.last_error = axolotl::ErrorCode::SUCCESS; + } + return result; +} + + +std::size_t axolotl::Session::decrypt_max_plaintext_length( + MessageType message_type, + std::uint8_t const * message, std::size_t message_length +) { + std::uint8_t const * message_body; + std::size_t message_body_length; + if (message_type == axolotl::MessageType::MESSAGE) { + message_body = message; + message_body_length = message_length; + } else { + axolotl::PreKeyMessageReader reader; + decode_one_time_key_message(reader, message, message_length); + if (!reader.message) { + last_error = axolotl::ErrorCode::BAD_MESSAGE_FORMAT; + return std::size_t(-1); + } + message_body = reader.message; + message_body_length = reader.message_length; + } + + std::size_t result = ratchet.decrypt_max_plaintext_length( + message_body, message_body_length + ); + + if (result == std::size_t(-1)) { + last_error = ratchet.last_error; + ratchet.last_error = axolotl::ErrorCode::SUCCESS; + } + return result; +} + + +std::size_t axolotl::Session::decrypt( + axolotl::MessageType message_type, + std::uint8_t const * message, std::size_t message_length, + std::uint8_t * plaintext, std::size_t max_plaintext_length +) { + std::uint8_t const * message_body; + std::size_t message_body_length; + if (message_type == axolotl::MessageType::MESSAGE) { + message_body = message; + message_body_length = message_length; + } else { + axolotl::PreKeyMessageReader reader; + decode_one_time_key_message(reader, message, message_length); + if (!reader.message) { + last_error = axolotl::ErrorCode::BAD_MESSAGE_FORMAT; + return std::size_t(-1); + } + message_body = reader.message; + message_body_length = reader.message_length; + } + + std::size_t result = ratchet.decrypt( + message_body, message_body_length, plaintext, max_plaintext_length + ); + + if (result == std::size_t(-1)) { + last_error = ratchet.last_error; + ratchet.last_error = axolotl::ErrorCode::SUCCESS; + } + return result; +} -- cgit v1.2.3