/* 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; /** * The cipher used in megolm-backed conversations * * (AES256 + SHA256, with keys based on an HKDF with info of MEGOLM_KEYS) */ extern 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_ */