olm/src/session.cpp

531 lines
17 KiB
C++

/* 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.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "olm/session.hh"
#include "olm/cipher.h"
#include "olm/crypto.h"
#include "olm/account.hh"
#include "olm/memory.hh"
#include "olm/message.hh"
#include "olm/pickle.hh"
#include <cstring>
#include <stdio.h>
namespace {
static const std::uint8_t PROTOCOL_VERSION = 0x3;
static const std::uint8_t ROOT_KDF_INFO[] = "OLM_ROOT";
static const std::uint8_t RATCHET_KDF_INFO[] = "OLM_RATCHET";
static const std::uint8_t CIPHER_KDF_INFO[] = "OLM_KEYS";
static const olm::KdfInfo OLM_KDF_INFO = {
ROOT_KDF_INFO, sizeof(ROOT_KDF_INFO) - 1,
RATCHET_KDF_INFO, sizeof(RATCHET_KDF_INFO) - 1
};
static const struct _olm_cipher_aes_sha_256 OLM_CIPHER =
OLM_CIPHER_INIT_AES_SHA_256(CIPHER_KDF_INFO);
} // namespace
olm::Session::Session(
) : ratchet(OLM_KDF_INFO, OLM_CIPHER_BASE(&OLM_CIPHER)),
last_error(OlmErrorCode::OLM_SUCCESS),
received_message(false) {
}
std::size_t olm::Session::new_outbound_session_random_length() const {
return CURVE25519_RANDOM_LENGTH * 2;
}
std::size_t olm::Session::new_outbound_session(
olm::Account const & local_account,
_olm_curve25519_public_key const & identity_key,
_olm_curve25519_public_key const & one_time_key,
std::uint8_t const * random, std::size_t random_length
) {
if (random_length < new_outbound_session_random_length()) {
last_error = OlmErrorCode::OLM_NOT_ENOUGH_RANDOM;
return std::size_t(-1);
}
_olm_curve25519_key_pair base_key;
_olm_crypto_curve25519_generate_key(random, &base_key);
_olm_curve25519_key_pair ratchet_key;
_olm_crypto_curve25519_generate_key(random + CURVE25519_RANDOM_LENGTH, &ratchet_key);
_olm_curve25519_key_pair const & alice_identity_key_pair = (
local_account.identity_keys.curve25519_key
);
received_message = false;
alice_identity_key = alice_identity_key_pair.public_key;
alice_base_key = base_key.public_key;
bob_one_time_key = one_time_key;
// Calculate the shared secret S via triple DH
std::uint8_t secret[3 * CURVE25519_SHARED_SECRET_LENGTH];
std::uint8_t * pos = secret;
_olm_crypto_curve25519_shared_secret(&alice_identity_key_pair, &one_time_key, pos);
pos += CURVE25519_SHARED_SECRET_LENGTH;
_olm_crypto_curve25519_shared_secret(&base_key, &identity_key, pos);
pos += CURVE25519_SHARED_SECRET_LENGTH;
_olm_crypto_curve25519_shared_secret(&base_key, &one_time_key, pos);
ratchet.initialise_as_alice(secret, sizeof(secret), ratchet_key);
olm::unset(base_key);
olm::unset(ratchet_key);
olm::unset(secret);
return std::size_t(0);
}
namespace {
static bool check_message_fields(
olm::PreKeyMessageReader & reader, bool have_their_identity_key
) {
bool ok = true;
ok = ok && (have_their_identity_key || reader.identity_key);
if (reader.identity_key) {
ok = ok && reader.identity_key_length == CURVE25519_KEY_LENGTH;
}
ok = ok && reader.message;
ok = ok && reader.base_key;
ok = ok && reader.base_key_length == CURVE25519_KEY_LENGTH;
ok = ok && reader.one_time_key;
ok = ok && reader.one_time_key_length == CURVE25519_KEY_LENGTH;
return ok;
}
} // namespace
std::size_t olm::Session::new_inbound_session(
olm::Account & local_account,
_olm_curve25519_public_key const * their_identity_key,
std::uint8_t const * one_time_key_message, std::size_t message_length
) {
olm::PreKeyMessageReader reader;
decode_one_time_key_message(reader, one_time_key_message, message_length);
if (!check_message_fields(reader, their_identity_key)) {
last_error = OlmErrorCode::OLM_BAD_MESSAGE_FORMAT;
return std::size_t(-1);
}
if (reader.identity_key && their_identity_key) {
bool same = 0 == std::memcmp(
their_identity_key->public_key, reader.identity_key, CURVE25519_KEY_LENGTH
);
if (!same) {
last_error = OlmErrorCode::OLM_BAD_MESSAGE_KEY_ID;
return std::size_t(-1);
}
}
olm::load_array(alice_identity_key.public_key, reader.identity_key);
olm::load_array(alice_base_key.public_key, reader.base_key);
olm::load_array(bob_one_time_key.public_key, reader.one_time_key);
olm::MessageReader message_reader;
decode_message(
message_reader, reader.message, reader.message_length,
ratchet.ratchet_cipher->ops->mac_length(ratchet.ratchet_cipher)
);
if (!message_reader.ratchet_key
|| message_reader.ratchet_key_length != CURVE25519_KEY_LENGTH) {
last_error = OlmErrorCode::OLM_BAD_MESSAGE_FORMAT;
return std::size_t(-1);
}
_olm_curve25519_public_key ratchet_key;
olm::load_array(ratchet_key.public_key, message_reader.ratchet_key);
olm::OneTimeKey const * our_one_time_key = local_account.lookup_key(
bob_one_time_key
);
if (!our_one_time_key) {
last_error = OlmErrorCode::OLM_BAD_MESSAGE_KEY_ID;
return std::size_t(-1);
}
_olm_curve25519_key_pair const & bob_identity_key = (
local_account.identity_keys.curve25519_key
);
_olm_curve25519_key_pair const & bob_one_time_key = our_one_time_key->key;
// Calculate the shared secret S via triple DH
std::uint8_t secret[CURVE25519_SHARED_SECRET_LENGTH * 3];
std::uint8_t * pos = secret;
_olm_crypto_curve25519_shared_secret(&bob_one_time_key, &alice_identity_key, pos);
pos += CURVE25519_SHARED_SECRET_LENGTH;
_olm_crypto_curve25519_shared_secret(&bob_identity_key, &alice_base_key, pos);
pos += CURVE25519_SHARED_SECRET_LENGTH;
_olm_crypto_curve25519_shared_secret(&bob_one_time_key, &alice_base_key, pos);
ratchet.initialise_as_bob(secret, sizeof(secret), ratchet_key);
olm::unset(secret);
return std::size_t(0);
}
std::size_t olm::Session::session_id_length() const {
return SHA256_OUTPUT_LENGTH;
}
std::size_t olm::Session::session_id(
std::uint8_t * id, std::size_t id_length
) {
if (id_length < session_id_length()) {
last_error = OlmErrorCode::OLM_OUTPUT_BUFFER_TOO_SMALL;
return std::size_t(-1);
}
std::uint8_t tmp[CURVE25519_KEY_LENGTH * 3];
std::uint8_t * pos = tmp;
pos = olm::store_array(pos, alice_identity_key.public_key);
pos = olm::store_array(pos, alice_base_key.public_key);
pos = olm::store_array(pos, bob_one_time_key.public_key);
_olm_crypto_sha256(tmp, sizeof(tmp), id);
return session_id_length();
}
bool olm::Session::matches_inbound_session(
_olm_curve25519_public_key const * their_identity_key,
std::uint8_t const * one_time_key_message, std::size_t message_length
) const {
olm::PreKeyMessageReader reader;
decode_one_time_key_message(reader, one_time_key_message, message_length);
if (!check_message_fields(reader, their_identity_key)) {
return false;
}
bool same = true;
if (reader.identity_key) {
same = same && 0 == std::memcmp(
reader.identity_key, alice_identity_key.public_key, CURVE25519_KEY_LENGTH
);
}
if (their_identity_key) {
same = same && 0 == std::memcmp(
their_identity_key->public_key, alice_identity_key.public_key,
CURVE25519_KEY_LENGTH
);
}
same = same && 0 == std::memcmp(
reader.base_key, alice_base_key.public_key, CURVE25519_KEY_LENGTH
);
same = same && 0 == std::memcmp(
reader.one_time_key, bob_one_time_key.public_key, CURVE25519_KEY_LENGTH
);
return same;
}
olm::MessageType olm::Session::encrypt_message_type() const {
if (received_message) {
return olm::MessageType::MESSAGE;
} else {
return olm::MessageType::PRE_KEY;
}
}
std::size_t olm::Session::encrypt_message_length(
std::size_t plaintext_length
) const {
std::size_t message_length = ratchet.encrypt_output_length(
plaintext_length
);
if (received_message) {
return message_length;
}
return encode_one_time_key_message_length(
CURVE25519_KEY_LENGTH,
CURVE25519_KEY_LENGTH,
CURVE25519_KEY_LENGTH,
message_length
);
}
std::size_t olm::Session::encrypt_random_length() const {
return ratchet.encrypt_random_length();
}
std::size_t olm::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 = OlmErrorCode::OLM_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 {
olm::PreKeyMessageWriter writer;
encode_one_time_key_message(
writer,
PROTOCOL_VERSION,
CURVE25519_KEY_LENGTH,
CURVE25519_KEY_LENGTH,
CURVE25519_KEY_LENGTH,
message_body_length,
message
);
olm::store_array(writer.one_time_key, bob_one_time_key.public_key);
olm::store_array(writer.identity_key, alice_identity_key.public_key);
olm::store_array(writer.base_key, alice_base_key.public_key);
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 = OlmErrorCode::OLM_SUCCESS;
return result;
}
return result;
}
std::size_t olm::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 == olm::MessageType::MESSAGE) {
message_body = message;
message_body_length = message_length;
} else {
olm::PreKeyMessageReader reader;
decode_one_time_key_message(reader, message, message_length);
if (!reader.message) {
last_error = OlmErrorCode::OLM_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 = OlmErrorCode::OLM_SUCCESS;
}
return result;
}
std::size_t olm::Session::decrypt(
olm::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 == olm::MessageType::MESSAGE) {
message_body = message;
message_body_length = message_length;
} else {
olm::PreKeyMessageReader reader;
decode_one_time_key_message(reader, message, message_length);
if (!reader.message) {
last_error = OlmErrorCode::OLM_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 = OlmErrorCode::OLM_SUCCESS;
return result;
}
received_message = true;
return result;
}
// make the description end with "..." instead of stopping abruptly with no
// warning
void elide_description(char *end) {
end[-3] = '.';
end[-2] = '.';
end[-1] = '.';
end[0] = '\0';
}
void olm::Session::describe(char *describe_buffer, size_t buflen) {
// how much of the buffer is remaining (this is an int rather than a size_t
// because it will get compared to the return value from snprintf)
int remaining = buflen;
// do nothing if we have a zero-length buffer, or if buflen > INT_MAX,
// resulting in an overflow
if (remaining <= 0) return;
describe_buffer[0] = '\0';
// we need at least 23 characters to get any sort of meaningful
// information, so bail if we don't have that. (But more importantly, we
// need it to be at least 4 so that elide_description doesn't go out of
// bounds.)
if (remaining < 23) return;
int size;
// check that snprintf didn't return an error or reach the end of the buffer
#define CHECK_SIZE_AND_ADVANCE \
if (size > remaining) { \
return elide_description(describe_buffer + remaining - 1); \
} else if (size > 0) { \
describe_buffer += size; \
remaining -= size; \
} else { \
return; \
}
size = snprintf(
describe_buffer, remaining,
"sender chain index: %d ", ratchet.sender_chain[0].chain_key.index
);
CHECK_SIZE_AND_ADVANCE;
size = snprintf(describe_buffer, remaining, "receiver chain indices:");
CHECK_SIZE_AND_ADVANCE;
for (size_t i = 0; i < ratchet.receiver_chains.size(); ++i) {
size = snprintf(
describe_buffer, remaining,
" %d", ratchet.receiver_chains[i].chain_key.index
);
CHECK_SIZE_AND_ADVANCE;
}
size = snprintf(describe_buffer, remaining, " skipped message keys:");
CHECK_SIZE_AND_ADVANCE;
for (size_t i = 0; i < ratchet.skipped_message_keys.size(); ++i) {
size = snprintf(
describe_buffer, remaining,
" %d", ratchet.skipped_message_keys[i].message_key.index
);
CHECK_SIZE_AND_ADVANCE;
}
#undef CHECK_SIZE_AND_ADVANCE
}
namespace {
// the master branch writes pickle version 1; the logging_enabled branch writes
// 0x80000001.
static const std::uint32_t SESSION_PICKLE_VERSION = 1;
}
std::size_t olm::pickle_length(
Session const & value
) {
std::size_t length = 0;
length += olm::pickle_length(SESSION_PICKLE_VERSION);
length += olm::pickle_length(value.received_message);
length += olm::pickle_length(value.alice_identity_key);
length += olm::pickle_length(value.alice_base_key);
length += olm::pickle_length(value.bob_one_time_key);
length += olm::pickle_length(value.ratchet);
return length;
}
std::uint8_t * olm::pickle(
std::uint8_t * pos,
Session const & value
) {
pos = olm::pickle(pos, SESSION_PICKLE_VERSION);
pos = olm::pickle(pos, value.received_message);
pos = olm::pickle(pos, value.alice_identity_key);
pos = olm::pickle(pos, value.alice_base_key);
pos = olm::pickle(pos, value.bob_one_time_key);
pos = olm::pickle(pos, value.ratchet);
return pos;
}
std::uint8_t const * olm::unpickle(
std::uint8_t const * pos, std::uint8_t const * end,
Session & value
) {
uint32_t pickle_version;
pos = olm::unpickle(pos, end, pickle_version); UNPICKLE_OK(pos);
bool includes_chain_index;
switch (pickle_version) {
case 1:
includes_chain_index = false;
break;
case 0x80000001UL:
includes_chain_index = true;
break;
default:
value.last_error = OlmErrorCode::OLM_UNKNOWN_PICKLE_VERSION;
return nullptr;
}
pos = olm::unpickle(pos, end, value.received_message); UNPICKLE_OK(pos);
pos = olm::unpickle(pos, end, value.alice_identity_key); UNPICKLE_OK(pos);
pos = olm::unpickle(pos, end, value.alice_base_key); UNPICKLE_OK(pos);
pos = olm::unpickle(pos, end, value.bob_one_time_key); UNPICKLE_OK(pos);
pos = olm::unpickle(pos, end, value.ratchet, includes_chain_index); UNPICKLE_OK(pos);
return pos;
}