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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.
*/
#ifndef OLM_MEGOLM_H_
#define OLM_MEGOLM_H_
/**
* implementation of the Megolm multi-part ratchet used in group chats.
*/
#include <stdint.h>
#include <stdlib.h>
#ifdef __cplusplus
extern "C" {
#endif
/**
* number of bytes in each part of the ratchet; this should be the same as
* the length of the hash function used in the HMAC (32 bytes for us, as we
* use HMAC-SHA-256)
*/
#define MEGOLM_RATCHET_PART_LENGTH 32 /* SHA256_OUTPUT_LENGTH */
/**
* number of parts in the ratchet; the advance() implementations rely on
* this being 4.
*/
#define MEGOLM_RATCHET_PARTS 4
#define MEGOLM_RATCHET_LENGTH (MEGOLM_RATCHET_PARTS * MEGOLM_RATCHET_PART_LENGTH)
typedef struct Megolm {
uint8_t data[MEGOLM_RATCHET_PARTS][MEGOLM_RATCHET_PART_LENGTH];
uint32_t counter;
} Megolm;
/**
* Get the cipher used in megolm-backed conversations
*
* (AES256 + SHA256, with keys based on an HKDF with info of MEGOLM_KEYS)
*/
const struct _olm_cipher *megolm_cipher();
/**
* initialize the megolm ratchet. random_data should be at least
* MEGOLM_RATCHET_LENGTH bytes of randomness.
*/
void megolm_init(Megolm *megolm, uint8_t const *random_data, uint32_t counter);
/** Returns the number of bytes needed to store a megolm */
size_t megolm_pickle_length(const Megolm *megolm);
/**
* Pickle the megolm. Returns a pointer to the next free space in the buffer.
*/
uint8_t * megolm_pickle(const Megolm *megolm, uint8_t *pos);
/**
* Unpickle the megolm. Returns a pointer to the next item in the buffer.
*/
const uint8_t * megolm_unpickle(Megolm *megolm, const uint8_t *pos,
const uint8_t *end);
/** advance the ratchet by one step */
void megolm_advance(Megolm *megolm);
/**
* get the key data in the ratchet. The returned data is
* MEGOLM_RATCHET_LENGTH bytes long.
*/
#define megolm_get_data(megolm) ((const uint8_t *)((megolm)->data))
/** advance the ratchet to a given count */
void megolm_advance_to(Megolm *megolm, uint32_t advance_to);
#ifdef __cplusplus
} // extern "C"
#endif
#endif /* OLM_MEGOLM_H_ */
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