mirror of https://git.matrix.org/git/olm.git
100 lines
2.8 KiB
C
100 lines
2.8 KiB
C
/* Copyright 2016 OpenMarket Ltd
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef OLM_MEGOLM_H_
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#define OLM_MEGOLM_H_
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/**
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* implementation of the Megolm multi-part ratchet used in group chats.
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*/
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#include <stdint.h>
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#include <stdlib.h>
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// Note: exports in this file are only for unit tests. Nobody else should be
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// using this externally
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#include "olm/olm_export.h"
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#ifdef __cplusplus
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extern "C" {
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#endif
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/**
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* number of bytes in each part of the ratchet; this should be the same as
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* the length of the hash function used in the HMAC (32 bytes for us, as we
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* use HMAC-SHA-256)
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*/
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#define MEGOLM_RATCHET_PART_LENGTH 32 /* SHA256_OUTPUT_LENGTH */
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/**
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* number of parts in the ratchet; the advance() implementations rely on
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* this being 4.
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*/
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#define MEGOLM_RATCHET_PARTS 4
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#define MEGOLM_RATCHET_LENGTH (MEGOLM_RATCHET_PARTS * MEGOLM_RATCHET_PART_LENGTH)
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typedef struct Megolm {
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uint8_t data[MEGOLM_RATCHET_PARTS][MEGOLM_RATCHET_PART_LENGTH];
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uint32_t counter;
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} Megolm;
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/**
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* The cipher used in megolm-backed conversations
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*
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* (AES256 + SHA256, with keys based on an HKDF with info of MEGOLM_KEYS)
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*/
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extern const struct _olm_cipher *megolm_cipher;
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/**
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* initialize the megolm ratchet. random_data should be at least
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* MEGOLM_RATCHET_LENGTH bytes of randomness.
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*/
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OLM_EXPORT void megolm_init(Megolm *megolm, uint8_t const *random_data, uint32_t counter);
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/** Returns the number of bytes needed to store a megolm */
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OLM_EXPORT size_t megolm_pickle_length(const Megolm *megolm);
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/**
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* Pickle the megolm. Returns a pointer to the next free space in the buffer.
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*/
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OLM_EXPORT uint8_t * megolm_pickle(const Megolm *megolm, uint8_t *pos);
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/**
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* Unpickle the megolm. Returns a pointer to the next item in the buffer.
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*/
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OLM_EXPORT const uint8_t * megolm_unpickle(Megolm *megolm, const uint8_t *pos,
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const uint8_t *end);
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/** advance the ratchet by one step */
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OLM_EXPORT void megolm_advance(Megolm *megolm);
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/**
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* get the key data in the ratchet. The returned data is
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* MEGOLM_RATCHET_LENGTH bytes long.
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*/
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#define megolm_get_data(megolm) ((const uint8_t *)((megolm)->data))
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/** advance the ratchet to a given count */
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OLM_EXPORT void megolm_advance_to(Megolm *megolm, uint32_t advance_to);
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#ifdef __cplusplus
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} // extern "C"
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#endif
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#endif /* OLM_MEGOLM_H_ */
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