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/*
* Copyright (c) 2020 Patrick Rathje
*
* SPDX-License-Identifier: Apache-2.0
*/
#ifndef EXPOSURE_NOTIFICATION_H
#define EXPOSURE_NOTIFICATION_H
#ifdef __cplusplus
extern "C" {
#endif
#include <time.h>
#include <stdint.h>
#include <stddef.h>
#ifndef EN_TEK_ROLLING_PERIOD
#define EN_TEK_ROLLING_PERIOD 144
#endif
#ifndef EN_INTERVAL_LENGTH
#define EN_INTERVAL_LENGTH 600
#endif
#ifndef EN_INIT_MBEDTLS_ENTROPY
#define EN_INIT_MBEDTLS_ENTROPY 1
#endif
/*
* Type: _ENBaseKey
* --------------------
* 16 Byte base key definition
*/
typedef struct _ENBaseKey { unsigned char b[16];} _ENBaseKey;
/*
* Type: ENIntervalNumber
* --------------------
* The number of the 10 minute interval
*/
typedef uint32_t ENIntervalNumber;
/*
* Type: ENPeriodKey
* --------------------
* 16 Byte temporary exposure key used throughout a rolling period (one day)
*/
typedef struct _ENBaseKey ENPeriodKey;
/*
* Type: ENPeriodIdentifierKey
* --------------------
* 16 Byte key used throughout each period to encrypt the identifier for each interval
*/
typedef struct _ENBaseKey ENPeriodIdentifierKey;
/*
* Type: ENIntervalIdentifier
* --------------------
* 16 Byte identifier used within the packet
*/
typedef struct _ENBaseKey ENIntervalIdentifier;
/*
* Type: ENPeriodMetadataEncryptionKey
* --------------------
* 16 Byte key used throughout each interval to encrypt the metadata within one period
*/
typedef struct _ENBaseKey ENPeriodMetadataEncryptionKey;
/*
* Type: ENPeriodMetadataEncryptionKey
* --------------------
* 16 Byte key used throughout each interval to encrypt the metadata within one period
*/
typedef struct _ENBaseKey ENPeriodMetadataEncryptionKey;
typedef int (*ENRandomBytesCallback)(void *buf, size_t len);
/*
* Function: en_init
* --------------------
* Initializes the random number generator. Use NULL to initialize with the fallback random_bytes_func
*/
int en_init(ENRandomBytesCallback user_random_bytes_callback);
/*
* Function: en_get_interval_number
* --------------------
* computes the interval number according to the given unix timestamp. Each interval lasts for EN_INTERVAL_LENGTH secs (defaults to 10 minutes).
*/
ENIntervalNumber en_get_interval_number(time_t timestamp);
/*
* Function: en_get_period_start_interval_number
* --------------------
* computes the first interval number for the period given by the unix timestamp.
*/
ENIntervalNumber en_get_interval_number_at_period_start(time_t timestamp);
/*
* Function: en_generate_period_key
* --------------------
* Generates a new period key using a cryptographic number generator. Used when the next period is dues (once a day).
*/
void en_generate_period_key(ENPeriodKey* periodKey);
/*
* Function: en_derive_period_identifier_key
* --------------------
* Derives the interval identifier key based on the current period key
*/
void en_derive_period_identifier_key(ENPeriodIdentifierKey *periodIdentifierKey, const ENPeriodKey *periodKey);
/*
* Function: en_derive_interval_identifier
* --------------------
* Get the identifier for a specific interval based on the identifierKey
*/
void en_derive_interval_identifier(ENIntervalIdentifier *intervalIdentifier, const ENPeriodIdentifierKey *periodIdentifierKey, const ENIntervalNumber intervalNumber);
/*
* Function: en_derive_period_metadata_encryption_key
* --------------------
* Derives the interval metadata encryption key based on the current period key
*/
void en_derive_period_metadata_encryption_key(ENPeriodMetadataEncryptionKey *periodMetadataEncryptionKey, const ENPeriodKey *periodKey);
/*
* Function: en_encrypt_interval_metadata
* --------------------
* Encrypts the metadata.
*/
void en_encrypt_interval_metadata(const ENPeriodMetadataEncryptionKey *periodMetadataEncryptionKey, const ENIntervalIdentifier *intervalIdentifier, unsigned char *input, unsigned char *output, size_t inputSize);
/*
* Function: en_decrypt_interval_metadata
* --------------------
* Decrypts the metadata.
*/
void en_decrypt_interval_metadata(const ENPeriodMetadataEncryptionKey *periodMetadataEncryptionKey, const ENIntervalIdentifier *intervalIdentifier, unsigned char *input, unsigned char *output, size_t inputSize);
/*
* Function: en_generate_period_relevant_keys()
* --------------------
* This function generates all period keys at once (convenient right?)
*/
static inline void en_generate_and_derive_period_keys(ENPeriodKey *periodKey, ENPeriodIdentifierKey *periodIdentifierKey, ENPeriodMetadataEncryptionKey *periodMetadataEncryptionKey) {
en_generate_period_key(periodKey);
en_derive_period_identifier_key(periodIdentifierKey, periodKey);
en_derive_period_metadata_encryption_key(periodMetadataEncryptionKey, periodKey);
}
#ifdef __cplusplus
}
#endif
#endif