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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/inbound_group_session.h"
#include <string.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
struct OlmInboundGroupSession {
/** our earliest known ratchet value */
Megolm initial_ratchet;
/** The most recent ratchet value */
Megolm latest_ratchet;
enum OlmErrorCode last_error;
};
size_t olm_inbound_group_session_size() {
return sizeof(OlmInboundGroupSession);
}
OlmInboundGroupSession * olm_inbound_group_session(
void *memory
) {
OlmInboundGroupSession *session = memory;
olm_clear_inbound_group_session(session);
return session;
}
const char *olm_inbound_group_session_last_error(
const OlmInboundGroupSession *session
) {
return _olm_error_to_string(session->last_error);
}
size_t olm_clear_inbound_group_session(
OlmInboundGroupSession *session
) {
memset(session, 0, sizeof(OlmInboundGroupSession));
return sizeof(OlmInboundGroupSession);
}
size_t olm_init_inbound_group_session(
OlmInboundGroupSession *session,
uint32_t message_index,
const uint8_t * session_key, size_t session_key_length
) {
uint8_t key_buf[MEGOLM_RATCHET_LENGTH];
size_t raw_length = _olm_decode_base64_length(session_key_length);
if (raw_length == (size_t)-1) {
session->last_error = OLM_INVALID_BASE64;
return (size_t)-1;
}
if (raw_length != MEGOLM_RATCHET_LENGTH) {
session->last_error = OLM_BAD_RATCHET_KEY;
return (size_t)-1;
}
_olm_decode_base64(session_key, session_key_length, key_buf);
megolm_init(&session->initial_ratchet, key_buf, message_index);
megolm_init(&session->latest_ratchet, key_buf, message_index);
memset(key_buf, 0, MEGOLM_RATCHET_LENGTH);
return 0;
}
size_t olm_group_decrypt_max_plaintext_length(
OlmInboundGroupSession *session,
uint8_t * message, size_t message_length
) {
size_t r;
const struct _olm_cipher *cipher = megolm_cipher();
struct _OlmDecodeGroupMessageResults decoded_results;
r = _olm_decode_base64(message, message_length, message);
if (r == (size_t)-1) {
session->last_error = OLM_INVALID_BASE64;
return r;
}
_olm_decode_group_message(
message, message_length,
cipher->ops->mac_length(cipher),
&decoded_results);
if (decoded_results.version != OLM_PROTOCOL_VERSION) {
session->last_error = OLM_BAD_MESSAGE_VERSION;
return (size_t)-1;
}
if (!decoded_results.ciphertext) {
session->last_error = OLM_BAD_MESSAGE_FORMAT;
return (size_t)-1;
}
return cipher->ops->decrypt_max_plaintext_length(
cipher, decoded_results.ciphertext_length);
}
size_t olm_group_decrypt(
OlmInboundGroupSession *session,
uint8_t * message, size_t message_length,
uint8_t * plaintext, size_t max_plaintext_length
) {
struct _OlmDecodeGroupMessageResults decoded_results;
const struct _olm_cipher *cipher = megolm_cipher();
size_t max_length, raw_message_length, r;
Megolm *megolm;
Megolm tmp_megolm;
raw_message_length = _olm_decode_base64(message, message_length, message);
if (raw_message_length == (size_t)-1) {
session->last_error = OLM_INVALID_BASE64;
return (size_t)-1;
}
_olm_decode_group_message(
message, raw_message_length,
cipher->ops->mac_length(cipher),
&decoded_results);
if (decoded_results.version != OLM_PROTOCOL_VERSION) {
session->last_error = OLM_BAD_MESSAGE_VERSION;
return (size_t)-1;
}
if (!decoded_results.has_chain_index || !decoded_results.session_id
|| !decoded_results.ciphertext
) {
session->last_error = OLM_BAD_MESSAGE_FORMAT;
return (size_t)-1;
}
max_length = cipher->ops->decrypt_max_plaintext_length(
cipher,
decoded_results.ciphertext_length
);
if (max_plaintext_length < max_length) {
session->last_error = OLM_OUTPUT_BUFFER_TOO_SMALL;
return (size_t)-1;
}
/* pick a megolm instance to use. If we're at or beyond the latest ratchet
* value, use that */
if ((int32_t)(decoded_results.chain_index - session->latest_ratchet.counter) >= 0) {
megolm = &session->latest_ratchet;
} else if ((int32_t)(decoded_results.chain_index - session->initial_ratchet.counter) < 0) {
/* the counter is before our intial ratchet - we can't decode this. */
session->last_error = OLM_BAD_CHAIN_INDEX;
return (size_t)-1;
} else {
/* otherwise, start from the initial megolm. Take a copy so that we
* don't overwrite the initial megolm */
tmp_megolm = session->initial_ratchet;
megolm = &tmp_megolm;
}
megolm_advance_to(megolm, decoded_results.chain_index);
/* now try checking the mac, and decrypting */
r = cipher->ops->decrypt(
cipher,
megolm_get_data(megolm), MEGOLM_RATCHET_LENGTH,
message, raw_message_length,
decoded_results.ciphertext, decoded_results.ciphertext_length,
plaintext, max_plaintext_length
);
memset(&tmp_megolm, 0, sizeof(tmp_megolm));
if (r == (size_t)-1) {
session->last_error = OLM_BAD_MESSAGE_MAC;
return r;
}
return r;
}
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