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/* Copyright 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/outbound_group_session.h"
#include <string.h>
#include <sys/time.h>
#include "olm/base64.h"
#include "olm/cipher.h"
#include "olm/error.h"
#include "olm/megolm.h"
#include "olm/message.h"
#define OLM_PROTOCOL_VERSION 3
#define SESSION_ID_RANDOM_BYTES 4
#define GROUP_SESSION_ID_LENGTH (sizeof(struct timeval) + SESSION_ID_RANDOM_BYTES)
struct OlmOutboundGroupSession {
/** the Megolm ratchet providing the encryption keys */
Megolm ratchet;
/** unique identifier for this session */
uint8_t session_id[GROUP_SESSION_ID_LENGTH];
enum OlmErrorCode last_error;
};
size_t olm_outbound_group_session_size() {
return sizeof(OlmOutboundGroupSession);
}
OlmOutboundGroupSession * olm_outbound_group_session(
void *memory
) {
OlmOutboundGroupSession *session = memory;
olm_clear_outbound_group_session(session);
return session;
}
const char *olm_outbound_group_session_last_error(
const OlmOutboundGroupSession *session
) {
return _olm_error_to_string(session->last_error);
}
size_t olm_clear_outbound_group_session(
OlmOutboundGroupSession *session
) {
memset(session, 0, sizeof(OlmOutboundGroupSession));
return sizeof(OlmOutboundGroupSession);
}
size_t olm_init_outbound_group_session_random_length(
const OlmOutboundGroupSession *session
) {
/* we need data to initialize the megolm ratchet, plus some more for the
* session id.
*/
return MEGOLM_RATCHET_LENGTH + SESSION_ID_RANDOM_BYTES;
}
size_t olm_init_outbound_group_session(
OlmOutboundGroupSession *session,
uint8_t const * random, size_t random_length
) {
if (random_length < olm_init_outbound_group_session_random_length(session)) {
/* Insufficient random data for new session */
session->last_error = OLM_NOT_ENOUGH_RANDOM;
return (size_t)-1;
}
megolm_init(&(session->ratchet), random, 0);
random += MEGOLM_RATCHET_LENGTH;
/* initialise the session id. This just has to be unique. We use the
* current time plus some random data.
*/
gettimeofday((struct timeval *)(session->session_id), NULL);
memcpy((session->session_id) + sizeof(struct timeval),
random, SESSION_ID_RANDOM_BYTES);
return 0;
}
static size_t raw_message_length(
OlmOutboundGroupSession *session,
size_t plaintext_length)
{
size_t ciphertext_length, mac_length;
const struct _olm_cipher *cipher = megolm_cipher();
ciphertext_length = cipher->ops->encrypt_ciphertext_length(
cipher, plaintext_length
);
mac_length = cipher->ops->mac_length(cipher);
return _olm_encode_group_message_length(
GROUP_SESSION_ID_LENGTH, session->ratchet.counter,
ciphertext_length, mac_length);
}
size_t olm_group_encrypt_message_length(
OlmOutboundGroupSession *session,
size_t plaintext_length
) {
size_t message_length = raw_message_length(session, plaintext_length);
return _olm_encode_base64_length(message_length);
}
size_t olm_group_encrypt(
OlmOutboundGroupSession *session,
uint8_t const * plaintext, size_t plaintext_length,
uint8_t * message, size_t max_message_length
) {
size_t ciphertext_length;
size_t rawmsglen;
size_t result;
uint8_t *ciphertext_ptr, *message_pos;
const struct _olm_cipher *cipher = megolm_cipher();
rawmsglen = raw_message_length(session, plaintext_length);
if (max_message_length < _olm_encode_base64_length(rawmsglen)) {
session->last_error = OLM_OUTPUT_BUFFER_TOO_SMALL;
return (size_t)-1;
}
ciphertext_length = cipher->ops->encrypt_ciphertext_length(
cipher,
plaintext_length
);
/* we construct the message at the end of the buffer, so that
* we have room to base64-encode it once we're done.
*/
message_pos = message + _olm_encode_base64_length(rawmsglen) - rawmsglen;
/* first we build the message structure, then we encrypt
* the plaintext into it.
*/
_olm_encode_group_message(
OLM_PROTOCOL_VERSION,
session->session_id, GROUP_SESSION_ID_LENGTH,
session->ratchet.counter,
ciphertext_length,
message_pos,
&ciphertext_ptr);
result = cipher->ops->encrypt(
cipher,
megolm_get_data(&(session->ratchet)), MEGOLM_RATCHET_LENGTH,
plaintext, plaintext_length,
ciphertext_ptr, ciphertext_length,
message_pos, rawmsglen
);
if (result == (size_t)-1) {
return result;
}
megolm_advance(&(session->ratchet));
return _olm_encode_base64(
message_pos, rawmsglen,
message
);
}
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