diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/cipher.cpp | 125 | ||||
| -rw-r--r-- | src/message.cpp | 39 | ||||
| -rw-r--r-- | src/ratchet.cpp | 218 |
3 files changed, 236 insertions, 146 deletions
diff --git a/src/cipher.cpp b/src/cipher.cpp new file mode 100644 index 0000000..86cde88 --- /dev/null +++ b/src/cipher.cpp @@ -0,0 +1,125 @@ +#include "axolotl/cipher.hh" +#include "axolotl/crypto.hh" +#include "axolotl/memory.hh" +#include <cstring> + +axolotl::Cipher::~Cipher() { + +} + +namespace { + +static const std::size_t SHA256_LENGTH = 32; + +struct DerivedKeys { + axolotl::Aes256Key aes_key; + std::uint8_t mac_key[SHA256_LENGTH]; + axolotl::Aes256Iv aes_iv; +}; + + +static void derive_keys( + std::uint8_t const * kdf_info, std::size_t kdf_info_length, + std::uint8_t const * key, std::size_t key_length, + DerivedKeys & keys +) { + std::uint8_t derived_secrets[80]; + axolotl::hkdf_sha256( + key, key_length, + NULL, 0, + kdf_info, kdf_info_length, + derived_secrets, sizeof(derived_secrets) + ); + std::memcpy(keys.aes_key.key, derived_secrets, 32); + std::memcpy(keys.mac_key, derived_secrets + 32, 32); + std::memcpy(keys.aes_iv.iv, derived_secrets + 64, 16); + axolotl::unset(derived_secrets); +} + +static const std::size_t MAC_LENGTH = 8; + +} // namespace + + +axolotl::CipherAesSha256::CipherAesSha256( + std::uint8_t const * kdf_info, std::size_t kdf_info_length +) : kdf_info(kdf_info), kdf_info_length(kdf_info_length) { + +} + + +std::size_t axolotl::CipherAesSha256::mac_length() const { + return MAC_LENGTH; +} + + +std::size_t axolotl::CipherAesSha256::encrypt_ciphertext_length( + std::size_t plaintext_length +) const { + return axolotl::aes_encrypt_cbc_length(plaintext_length); +} + + +std::size_t axolotl::CipherAesSha256::encrypt( + std::uint8_t const * key, std::size_t key_length, + std::uint8_t const * plaintext, std::size_t plaintext_length, + std::uint8_t * ciphertext, std::size_t ciphertext_length, + std::uint8_t * output, std::size_t output_length +) const { + if (encrypt_ciphertext_length(plaintext_length) < ciphertext_length) { + return std::size_t(-1); + } + struct DerivedKeys keys; + std::uint8_t mac[SHA256_LENGTH]; + + derive_keys(kdf_info, kdf_info_length, key, key_length, keys); + + axolotl::aes_encrypt_cbc( + keys.aes_key, keys.aes_iv, plaintext, plaintext_length, ciphertext + ); + + axolotl::hmac_sha256( + keys.mac_key, SHA256_LENGTH, output, output_length - MAC_LENGTH, mac + ); + + std::memcpy(output + output_length - MAC_LENGTH, mac, MAC_LENGTH); + + axolotl::unset(keys); + return output_length; +} + + +std::size_t axolotl::CipherAesSha256::decrypt_max_plaintext_length( + std::size_t ciphertext_length +) const { + return ciphertext_length; +} + +std::size_t axolotl::CipherAesSha256::decrypt( + std::uint8_t const * key, std::size_t key_length, + std::uint8_t const * input, std::size_t input_length, + std::uint8_t const * ciphertext, std::size_t ciphertext_length, + std::uint8_t * plaintext, std::size_t max_plaintext_length +) const { + DerivedKeys keys; + std::uint8_t mac[SHA256_LENGTH]; + + derive_keys(kdf_info, kdf_info_length, key, key_length, keys); + + axolotl::hmac_sha256( + keys.mac_key, SHA256_LENGTH, input, input_length - MAC_LENGTH, mac + ); + + std::uint8_t const * input_mac = input + input_length - MAC_LENGTH; + if (!axolotl::is_equal(input_mac, mac, MAC_LENGTH)) { + axolotl::unset(keys); + return std::size_t(-1); + } + + std::size_t plaintext_length = axolotl::aes_decrypt_cbc( + keys.aes_key, keys.aes_iv, ciphertext, ciphertext_length, plaintext + ); + + axolotl::unset(keys); + return plaintext_length; +} diff --git a/src/message.cpp b/src/message.cpp index 289faa3..46cadd8 100644 --- a/src/message.cpp +++ b/src/message.cpp @@ -94,55 +94,52 @@ std::size_t axolotl::encode_message_length( length += 1 + varstring_length(ratchet_key_length); length += 1 + varint_length(counter); length += 1 + varstring_length(ciphertext_length); - return length + mac_length; + length += mac_length; + return length; } -axolotl::MessageWriter axolotl::encode_message( +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 ) { - 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; + writer.ratchet_key = pos; pos += ratchet_key_length; *(pos++) = CIPHERTEXT_TAG; pos = varint_encode(pos, ciphertext_length); - result.ciphertext = pos; + writer.ciphertext = pos; pos += ciphertext_length; - result.body_length = pos - output; - result.mac = pos; - return result; } -axolotl::MessageReader axolotl::decode_message( +std::size_t axolotl::decode_message( + axolotl::MessageReader & reader, 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; + std::size_t result = std::size_t(-1); if (pos == end) return result; - result.version = *(pos++); + 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); - result.counter = varint_decode<std::uint32_t>(counter_start, pos); + reader.counter = varint_decode<std::uint32_t>(counter_start, pos); flags |= 1; } else if (tag == RATCHET_KEY_TAG) { ++pos; @@ -150,8 +147,8 @@ axolotl::MessageReader axolotl::decode_message( 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; + reader.ratchet_key_length = len; + reader.ratchet_key = pos; pos += len; flags |= 2; } else if (tag == CIPHERTEXT_TAG) { @@ -160,8 +157,8 @@ axolotl::MessageReader axolotl::decode_message( 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; + reader.ciphertext_length = len; + reader.ciphertext = pos; pos += len; flags |= 4; } else if (tag & 0x7 == 0) { @@ -174,11 +171,13 @@ axolotl::MessageReader axolotl::decode_message( if (len > end - pos) return result; pos += len; } else { - return result; + return std::size_t(-1); } } if (flags == 0x7) { - result.body_length = end - input; + reader.input = input; + reader.input_length = input_length; + return std::size_t(pos - input); } return result; } diff --git a/src/ratchet.cpp b/src/ratchet.cpp index b17e162..cd4f8f7 100644 --- a/src/ratchet.cpp +++ b/src/ratchet.cpp @@ -15,13 +15,13 @@ #include "axolotl/ratchet.hh" #include "axolotl/message.hh" #include "axolotl/memory.hh" +#include "axolotl/cipher.hh" #include <cstring> namespace { std::uint8_t PROTOCOL_VERSION = 3; -std::size_t MAC_LENGTH = 8; std::size_t KEY_LENGTH = axolotl::Curve25519PublicKey::LENGTH; std::uint8_t MESSAGE_KEY_SEED[1] = {0x01}; std::uint8_t CHAIN_KEY_SEED[1] = {0x02}; @@ -70,59 +70,43 @@ void create_message_keys( axolotl::KdfInfo const & info, axolotl::MessageKey & message_key ) { - axolotl::SharedKey secret; axolotl::hmac_sha256( chain_key.key, sizeof(chain_key.key), MESSAGE_KEY_SEED, sizeof(MESSAGE_KEY_SEED), - secret + message_key.key ); - std::uint8_t derived_secrets[80]; - axolotl::hkdf_sha256( - secret, sizeof(secret), - NULL, 0, - info.message_info, info.message_info_length, - derived_secrets, sizeof(derived_secrets) - ); - std::memcpy(message_key.cipher_key.key, derived_secrets, 32); - std::memcpy(message_key.mac_key, derived_secrets + 32, 32); - std::memcpy(message_key.iv.iv, derived_secrets + 64, 16); message_key.index = chain_key.index; - axolotl::unset(derived_secrets); - axolotl::unset(secret); } -bool verify_mac( +std::size_t verify_mac_and_decrypt( + axolotl::Cipher const & cipher, axolotl::MessageKey const & message_key, - std::uint8_t const * input, - axolotl::MessageReader const & reader + axolotl::MessageReader const & reader, + std::uint8_t * plaintext, std::size_t max_plaintext_length ) { - std::uint8_t mac[axolotl::HMAC_SHA256_OUTPUT_LENGTH]; - axolotl::hmac_sha256( - message_key.mac_key, sizeof(message_key.mac_key), - input, reader.body_length, - mac + return cipher.decrypt( + message_key.key, sizeof(message_key.key), + reader.input, reader.input_length, + reader.ciphertext, reader.ciphertext_length, + plaintext, max_plaintext_length ); - - bool result = axolotl::is_equal(mac, reader.mac, MAC_LENGTH); - axolotl::unset(mac); - return result; } -bool verify_mac_for_existing_chain( +std::size_t verify_mac_and_decrypt_for_existing_chain( axolotl::Session const & session, axolotl::ChainKey const & chain, - std::uint8_t const * input, - axolotl::MessageReader const & reader + axolotl::MessageReader const & reader, + std::uint8_t * plaintext, std::size_t max_plaintext_length ) { if (reader.counter < chain.index) { - return false; + return std::size_t(-1); } /* Limit the number of hashes we're prepared to compute */ if (reader.counter - chain.index > MAX_MESSAGE_GAP) { - return false; + return std::size_t(-1); } axolotl::ChainKey new_chain = chain; @@ -134,16 +118,20 @@ bool verify_mac_for_existing_chain( axolotl::MessageKey message_key; create_message_keys(new_chain, session.kdf_info, message_key); - bool result = verify_mac(message_key, input, reader); + std::size_t result = verify_mac_and_decrypt( + session.ratchet_cipher, message_key, reader, + plaintext, max_plaintext_length + ); + axolotl::unset(new_chain); return result; } -bool verify_mac_for_new_chain( +std::size_t verify_mac_and_decrypt_for_new_chain( axolotl::Session const & session, - std::uint8_t const * input, - axolotl::MessageReader const & reader + axolotl::MessageReader const & reader, + std::uint8_t * plaintext, std::size_t max_plaintext_length ) { axolotl::SharedKey new_root_key; axolotl::ReceiverChain new_chain; @@ -168,8 +156,9 @@ bool verify_mac_for_new_chain( new_root_key, new_chain.chain_key ); - bool result = verify_mac_for_existing_chain( - session, new_chain.chain_key, input, reader + std::size_t result = verify_mac_and_decrypt_for_existing_chain( + session, new_chain.chain_key, reader, + plaintext, max_plaintext_length ); axolotl::unset(new_root_key); axolotl::unset(new_chain); @@ -180,8 +169,11 @@ bool verify_mac_for_new_chain( axolotl::Session::Session( - axolotl::KdfInfo const & kdf_info -) : kdf_info(kdf_info), last_error(axolotl::ErrorCode::SUCCESS) { + axolotl::KdfInfo const & kdf_info, + Cipher const & ratchet_cipher +) : kdf_info(kdf_info), + ratchet_cipher(ratchet_cipher), + last_error(axolotl::ErrorCode::SUCCESS) { } @@ -232,7 +224,7 @@ std::size_t axolotl::Session::pickle_max_output_length() { pickle_length += sender_chain.size() * send_chain_length; pickle_length += receiver_chains.size() * recv_chain_length; pickle_length += skipped_message_keys.size() * skip_key_length; - return axolotl::aes_encrypt_cbc_length(pickle_length) + MAC_LENGTH; + return pickle_length; } namespace { @@ -299,11 +291,10 @@ std::size_t axolotl::Session::pickle( } for (const axolotl::SkippedMessageKey &key : skipped_message_keys) { pos = pickle_counter(pos, key.message_key.index); - pos = pickle_bytes(pos, 32, key.message_key.cipher_key.key); - pos = pickle_bytes(pos, 32, key.message_key.mac_key); - pos = pickle_bytes(pos, 16, key.message_key.iv.iv); + pos = pickle_bytes(pos, 32, key.message_key.key); pos = pickle_bytes(pos, 32, key.ratchet_key.public_key); } + return pos - output; } std::size_t axolotl::Session::unpickle( @@ -352,11 +343,10 @@ std::size_t axolotl::Session::unpickle( skipped_message_keys.end() ); pos = unpickle_counter(pos, key.message_key.index); - pos = unpickle_bytes(pos, 32, key.message_key.cipher_key.key); - pos = unpickle_bytes(pos, 32, key.message_key.mac_key); - pos = unpickle_bytes(pos, 16, key.message_key.iv.iv); + pos = unpickle_bytes(pos, 32, key.message_key.key); pos = unpickle_bytes(pos, 32, key.ratchet_key.public_key); } + return pos - input; } @@ -369,7 +359,7 @@ std::size_t axolotl::Session::encrypt_max_output_length( } std::size_t padded = axolotl::aes_encrypt_cbc_length(plaintext_length); return axolotl::encode_message_length( - counter, KEY_LENGTH, padded, MAC_LENGTH + counter, KEY_LENGTH, padded, ratchet_cipher.mac_length() ); } @@ -384,11 +374,13 @@ std::size_t axolotl::Session::encrypt( std::uint8_t const * random, std::size_t random_length, std::uint8_t * output, std::size_t max_output_length ) { + std::size_t output_length = encrypt_max_output_length(plaintext_length); + if (random_length < encrypt_random_length()) { last_error = axolotl::ErrorCode::NOT_ENOUGH_RANDOM; return std::size_t(-1); } - if (max_output_length < encrypt_max_output_length(plaintext_length)) { + if (max_output_length < output_length) { last_error = axolotl::ErrorCode::OUTPUT_BUFFER_TOO_SMALL; return std::size_t(-1); } @@ -409,32 +401,29 @@ std::size_t axolotl::Session::encrypt( create_message_keys(sender_chain[0].chain_key, kdf_info, keys); advance_chain_key(sender_chain[0].chain_key, sender_chain[0].chain_key); - std::size_t padded = axolotl::aes_encrypt_cbc_length(plaintext_length); + std::size_t ciphertext_length = ratchet_cipher.encrypt_ciphertext_length( + plaintext_length + ); std::uint32_t counter = keys.index; Curve25519PublicKey const & ratchet_key = sender_chain[0].ratchet_key; - axolotl::MessageWriter writer(axolotl::encode_message( - PROTOCOL_VERSION, counter, KEY_LENGTH, padded, output - )); + axolotl::MessageWriter writer; + + axolotl::encode_message( + writer, PROTOCOL_VERSION, counter, KEY_LENGTH, ciphertext_length, output + ); std::memcpy(writer.ratchet_key, ratchet_key.public_key, KEY_LENGTH); - axolotl::aes_encrypt_cbc( - keys.cipher_key, keys.iv, + ratchet_cipher.encrypt( + keys.key, sizeof(keys.key), plaintext, plaintext_length, - writer.ciphertext + writer.ciphertext, ciphertext_length, + output, output_length ); - std::uint8_t mac[axolotl::HMAC_SHA256_OUTPUT_LENGTH]; - axolotl::hmac_sha256( - keys.mac_key, sizeof(keys.mac_key), - output, writer.body_length, - mac - ); - std::memcpy(writer.mac, mac, MAC_LENGTH); - axolotl::unset(keys); - return writer.body_length + MAC_LENGTH; + return output_length; } @@ -454,16 +443,17 @@ std::size_t axolotl::Session::decrypt( return std::size_t(-1); } - axolotl::MessageReader reader(axolotl::decode_message( - input, input_length, MAC_LENGTH - )); + axolotl::MessageReader reader; + std::size_t body_length = axolotl::decode_message( + reader, input, input_length, ratchet_cipher.mac_length() + ); if (reader.version != PROTOCOL_VERSION) { last_error = axolotl::ErrorCode::BAD_MESSAGE_VERSION; return std::size_t(-1); } - if (reader.body_length == 0 || reader.ratchet_key_length != KEY_LENGTH) { + if (body_length == size_t(-1) || reader.ratchet_key_length != KEY_LENGTH) { last_error = axolotl::ErrorCode::BAD_MESSAGE_FORMAT; return std::size_t(-1); } @@ -479,40 +469,30 @@ std::size_t axolotl::Session::decrypt( } } - if (!chain) { - if (!verify_mac_for_new_chain(*this, input, reader)) { - last_error = axolotl::ErrorCode::BAD_MESSAGE_MAC; - return std::size_t(-1); - } - } else { - if (chain->chain_key.index > reader.counter) { - /* Chain already advanced beyond the key for this message - * Check if the message keys are in the skipped key list. */ - for (axolotl::SkippedMessageKey & skipped : skipped_message_keys) { - if (reader.counter == skipped.message_key.index - && 0 == std::memcmp( - skipped.ratchet_key.public_key, reader.ratchet_key, - KEY_LENGTH - ) - ) { - /* Found the key for this message. Check the MAC. */ - if (!verify_mac(skipped.message_key, input, reader)) { - last_error = axolotl::ErrorCode::BAD_MESSAGE_MAC; - return std::size_t(-1); - } - - std::size_t result = axolotl::aes_decrypt_cbc( - skipped.message_key.cipher_key, - skipped.message_key.iv, - reader.ciphertext, reader.ciphertext_length, - plaintext - ); - - if (result == std::size_t(-1)) { - last_error = axolotl::ErrorCode::BAD_MESSAGE_MAC; - return result; - } + std::size_t result = std::size_t(-1); + if (!chain) { + result = verify_mac_and_decrypt_for_new_chain( + *this, reader, plaintext, max_plaintext_length + ); + } else if (chain->chain_key.index > reader.counter) { + /* Chain already advanced beyond the key for this message + * Check if the message keys are in the skipped key list. */ + for (axolotl::SkippedMessageKey & skipped : skipped_message_keys) { + if (reader.counter == skipped.message_key.index + && 0 == std::memcmp( + skipped.ratchet_key.public_key, reader.ratchet_key, + KEY_LENGTH + ) + ) { + /* Found the key for this message. Check the MAC. */ + + result = verify_mac_and_decrypt( + ratchet_cipher, skipped.message_key, reader, + plaintext, max_plaintext_length + ); + + if (result != std::size_t(-1)) { /* Remove the key from the skipped keys now that we've * decoded the message it corresponds to. */ axolotl::unset(skipped); @@ -520,15 +500,16 @@ std::size_t axolotl::Session::decrypt( return result; } } - /* No matching keys for the message, fail with bad mac */ - last_error = axolotl::ErrorCode::BAD_MESSAGE_MAC; - return std::size_t(-1); - } else if (!verify_mac_for_existing_chain( - *this, chain->chain_key, input, reader - )) { - last_error = axolotl::ErrorCode::BAD_MESSAGE_MAC; - return std::size_t(-1); } + } else { + result = verify_mac_and_decrypt_for_existing_chain( + *this, chain->chain_key, reader, plaintext, max_plaintext_length + ); + } + + if (result == std::size_t(-1)) { + last_error = axolotl::ErrorCode::BAD_MESSAGE_MAC; + return std::size_t(-1); } if (!chain) { @@ -555,22 +536,7 @@ std::size_t axolotl::Session::decrypt( advance_chain_key(chain->chain_key, chain->chain_key); } - axolotl::MessageKey message_key; - create_message_keys(chain->chain_key, kdf_info, message_key); - std::size_t result = axolotl::aes_decrypt_cbc( - message_key.cipher_key, - message_key.iv, - reader.ciphertext, reader.ciphertext_length, - plaintext - ); - axolotl::unset(message_key); - advance_chain_key(chain->chain_key, chain->chain_key); - if (result == std::size_t(-1)) { - last_error = axolotl::ErrorCode::BAD_MESSAGE_MAC; - return std::size_t(-1); - } else { - return result; - } + return result; } |