diff options
Diffstat (limited to 'src/ratchet.cpp')
| -rw-r--r-- | src/ratchet.cpp | 95 |
1 files changed, 81 insertions, 14 deletions
diff --git a/src/ratchet.cpp b/src/ratchet.cpp index 5ef1e56..03a0478 100644 --- a/src/ratchet.cpp +++ b/src/ratchet.cpp @@ -1,4 +1,4 @@ -/* Copyright 2015 OpenMarket Ltd +/* Copyright 2015, 2016 OpenMarket Ltd * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. @@ -17,17 +17,31 @@ #include "olm/memory.hh" #include "olm/cipher.hh" #include "olm/pickle.hh" - +#include "olm/logging.hh" #include <cstring> namespace { +static const char *LOG_CATEGORY = "olm::Ratchet"; + static const std::uint8_t PROTOCOL_VERSION = 3; static const std::uint8_t MESSAGE_KEY_SEED[1] = {0x01}; static const std::uint8_t CHAIN_KEY_SEED[1] = {0x02}; static const std::size_t MAX_MESSAGE_GAP = 2000; + +/** + * Advance the root key, creating a new message chain. + * + * @param root_key previous root key R(n-1) + * @param our_key our new ratchet key T(n) + * @param their_key their most recent ratchet key T(n-1) + * @param info table of constants for the ratchet function + * @param new_root_key[out] returns the new root key R(n) + * @param new_chain_key[out] returns the first chain key in the new chain + * C(n,0) + */ static void create_chain_key( olm::SharedKey const & root_key, olm::Curve25519KeyPair const & our_key, @@ -55,6 +69,7 @@ static void create_chain_key( static void advance_chain_key( + std::uint32_t chain_index, olm::ChainKey const & chain_key, olm::ChainKey & new_chain_key ) { @@ -64,20 +79,24 @@ static void advance_chain_key( new_chain_key.key ); new_chain_key.index = chain_key.index + 1; + olm::logf(olm::LOG_DEBUG, LOG_CATEGORY, "Derived chain key C(%i,%i)", + chain_index, new_chain_key.index); } static void create_message_keys( + std::uint32_t chain_index, olm::ChainKey const & chain_key, olm::KdfInfo const & info, - olm::MessageKey & message_key -) { + olm::MessageKey & message_key) { olm::hmac_sha256( chain_key.key, sizeof(chain_key.key), MESSAGE_KEY_SEED, sizeof(MESSAGE_KEY_SEED), message_key.key ); message_key.index = chain_key.index; + olm::logf(olm::LOG_DEBUG, LOG_CATEGORY, "Created message key with chain key C(%i,%i)", + chain_index, message_key.index); } @@ -98,6 +117,7 @@ static std::size_t verify_mac_and_decrypt( static std::size_t verify_mac_and_decrypt_for_existing_chain( olm::Ratchet const & session, + std::uint32_t chain_index, olm::ChainKey const & chain, olm::MessageReader const & reader, std::uint8_t * plaintext, std::size_t max_plaintext_length @@ -114,11 +134,11 @@ static std::size_t verify_mac_and_decrypt_for_existing_chain( olm::ChainKey new_chain = chain; while (new_chain.index < reader.counter) { - advance_chain_key(new_chain, new_chain); + advance_chain_key(chain_index, new_chain, new_chain); } olm::MessageKey message_key; - create_message_keys(new_chain, session.kdf_info, message_key); + create_message_keys(chain_index, new_chain, session.kdf_info, message_key); std::size_t result = verify_mac_and_decrypt( session.ratchet_cipher, message_key, reader, @@ -150,14 +170,17 @@ static std::size_t verify_mac_and_decrypt_for_new_chain( } olm::load_array(new_chain.ratchet_key.public_key, reader.ratchet_key); + std::uint32_t chain_index = session.chain_index + 1; create_chain_key( session.root_key, session.sender_chain[0].ratchet_key, new_chain.ratchet_key, session.kdf_info, new_root_key, new_chain.chain_key ); + olm::logf(olm::LOG_DEBUG, LOG_CATEGORY, "Calculated new receiver chain R(%i)", + chain_index); std::size_t result = verify_mac_and_decrypt_for_existing_chain( - session, new_chain.chain_key, reader, + session, chain_index, new_chain.chain_key, reader, plaintext, max_plaintext_length ); olm::unset(new_root_key); @@ -194,7 +217,9 @@ void olm::Ratchet::initialise_as_bob( pos = olm::load_array(root_key, pos); pos = olm::load_array(receiver_chains[0].chain_key.key, pos); receiver_chains[0].ratchet_key = their_ratchet_key; + chain_index = 0; olm::unset(derived_secrets); + olm::logf(olm::LOG_DEBUG, LOG_CATEGORY, "Initialised receiver chain R(0)"); } @@ -215,7 +240,9 @@ void olm::Ratchet::initialise_as_alice( pos = olm::load_array(root_key, pos); pos = olm::load_array(sender_chain[0].chain_key.key, pos); sender_chain[0].ratchet_key = our_ratchet_key; + chain_index = 0; olm::unset(derived_secrets); + olm::logf(olm::LOG_DEBUG, LOG_CATEGORY, "Initialised sender chain R(0)"); } namespace olm { @@ -353,6 +380,7 @@ std::size_t olm::pickle_length( length += olm::pickle_length(value.sender_chain); length += olm::pickle_length(value.receiver_chains); length += olm::pickle_length(value.skipped_message_keys); + length += olm::pickle_length(value.chain_index); return length; } @@ -364,6 +392,7 @@ std::uint8_t * olm::pickle( pos = pickle(pos, value.sender_chain); pos = pickle(pos, value.receiver_chains); pos = pickle(pos, value.skipped_message_keys); + pos = pickle(pos, value.chain_index); return pos; } @@ -376,6 +405,7 @@ std::uint8_t const * olm::unpickle( pos = unpickle(pos, end, value.sender_chain); pos = unpickle(pos, end, value.receiver_chains); pos = unpickle(pos, end, value.skipped_message_keys); + pos = unpickle(pos, end, value.chain_index); return pos; } @@ -420,6 +450,9 @@ std::size_t olm::Ratchet::encrypt( if (sender_chain.empty()) { sender_chain.insert(); olm::curve25519_generate_key(random, sender_chain[0].ratchet_key); + olm::logf(olm::LOG_DEBUG, LOG_CATEGORY, "Created new ratchet key T(%i) %s", + chain_index + 1, + sender_chain[0].ratchet_key.to_string().c_str()); create_chain_key( root_key, sender_chain[0].ratchet_key, @@ -427,11 +460,14 @@ std::size_t olm::Ratchet::encrypt( kdf_info, root_key, sender_chain[0].chain_key ); + olm::logf(olm::LOG_DEBUG, LOG_CATEGORY, "Initialised new sender chain R(%i)", + chain_index + 1); + chain_index++; } MessageKey keys; - create_message_keys(sender_chain[0].chain_key, kdf_info, keys); - advance_chain_key(sender_chain[0].chain_key, sender_chain[0].chain_key); + create_message_keys(chain_index, sender_chain[0].chain_key, kdf_info, keys); + advance_chain_key(chain_index, sender_chain[0].chain_key, sender_chain[0].chain_key); std::size_t ciphertext_length = ratchet_cipher.encrypt_ciphertext_length( plaintext_length @@ -455,6 +491,14 @@ std::size_t olm::Ratchet::encrypt( output, output_length ); + olm::logf(olm::LOG_TRACE, LOG_CATEGORY, + "Encoded message ver=%i ratchet_key=%s chain_idx=%i ciphertext=%s", + PROTOCOL_VERSION, + olm::bytes_to_string(writer.ratchet_key, olm::KEY_LENGTH).c_str(), + counter, + olm::bytes_to_string(writer.ciphertext, ciphertext_length).c_str() + ); + olm::unset(keys); return output_length; } @@ -481,6 +525,10 @@ std::size_t olm::Ratchet::decrypt( std::uint8_t const * input, std::size_t input_length, std::uint8_t * plaintext, std::size_t max_plaintext_length ) { + olm::logf(olm::LOG_TRACE, LOG_CATEGORY, + "Decrypting message %s", + olm::bytes_to_string(input, input_length).c_str()); + olm::MessageReader reader; olm::decode_message( reader, input, input_length, ratchet_cipher.mac_length() @@ -511,6 +559,13 @@ std::size_t olm::Ratchet::decrypt( } ReceiverChain * chain = nullptr; + auto receiver_chain_index = chain_index; + if (!sender_chain.empty()) { + // we've already advanced to the next (sender) chain; decrement to + // get back to the receiver chains + receiver_chain_index --; + } + for (olm::ReceiverChain & receiver_chain : receiver_chains) { if (0 == std::memcmp( receiver_chain.ratchet_key.public_key, reader.ratchet_key, @@ -519,11 +574,14 @@ std::size_t olm::Ratchet::decrypt( chain = &receiver_chain; break; } + receiver_chain_index -= 2; } std::size_t result = std::size_t(-1); if (!chain) { + olm::logf(olm::LOG_DEBUG, LOG_CATEGORY, + "Sender ratchet key does not match known chain; starting new one"); result = verify_mac_and_decrypt_for_new_chain( *this, reader, plaintext, max_plaintext_length ); @@ -555,7 +613,8 @@ std::size_t olm::Ratchet::decrypt( } } else { result = verify_mac_and_decrypt_for_existing_chain( - *this, chain->chain_key, reader, plaintext, max_plaintext_length + *this, receiver_chain_index, chain->chain_key, + reader, plaintext, max_plaintext_length ); } @@ -565,28 +624,36 @@ std::size_t olm::Ratchet::decrypt( } if (!chain) { - /* They have started using a new empheral ratchet key. + /* They have started using a new ephemeral ratchet key. * We need to derive a new set of chain keys. * We can discard our previous empheral ratchet key. * We will generate a new key when we send the next message. */ + chain = receiver_chains.insert(); olm::load_array(chain->ratchet_key.public_key, reader.ratchet_key); + + // TODO: we've already done this once, in + // verify_mac_and_decrypt_for_new_chain(). we could reuse the result. create_chain_key( root_key, sender_chain[0].ratchet_key, chain->ratchet_key, kdf_info, root_key, chain->chain_key ); + olm::unset(sender_chain[0]); sender_chain.erase(sender_chain.begin()); + receiver_chain_index = ++chain_index; + olm::logf(olm::LOG_DEBUG, LOG_CATEGORY, "Initialised new receiver chain R(%i)", + chain_index); } while (chain->chain_key.index < reader.counter) { olm::SkippedMessageKey & key = *skipped_message_keys.insert(); - create_message_keys(chain->chain_key, kdf_info, key.message_key); + create_message_keys(receiver_chain_index, chain->chain_key, kdf_info, key.message_key); key.ratchet_key = chain->ratchet_key; - advance_chain_key(chain->chain_key, chain->chain_key); + advance_chain_key(receiver_chain_index, chain->chain_key, chain->chain_key); } - advance_chain_key(chain->chain_key, chain->chain_key); + advance_chain_key(receiver_chain_index, chain->chain_key, chain->chain_key); return result; } |