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Use PlatformIO Exposure Notification Library

pull/5/head
Patrick Rathje 7 months ago
parent
commit
8dc0dd74e4
  1. 52
      lib/exposure-notification/examples/tracking.c
  2. 170
      lib/exposure-notification/include/exposure-notification.h
  3. 14
      lib/exposure-notification/library.json
  4. 140
      lib/exposure-notification/src/exposure-notification.c
  5. 8
      platformio.ini

52
lib/exposure-notification/examples/tracking.c

@ -1,52 +0,0 @@
#include "exposure-notification.h"
#include "time.h"
int main(int argc, char **argv) {
// first init everything
// TODO: More randomization, we init with NULL to let en init mbdet entropy for us
en_init(NULL);
// get the currentTime
time_t currentTime = time(NULL);
// The periodKey changes each EN_TEK_ROLLING_PERIOD intervals
ENIntervalNumber periodInterval = en_get_interval_number_at_period_start(currentTime);
ENPeriodKey periodKey;
ENPeriodIdentifierKey periodIdentifierKey;
ENPeriodMetadataEncryptionKey periodMetadaEncryptionKey;
// setup period keys at the beginning
// in theory you could let them generate automatically setting periodInterval to 0
en_generate_and_derive_period_keys(&periodKey, &periodIdentifierKey, &periodMetadaEncryptionKey);
char metadata[128] = "";
while(1) {
// we check the current time to know if we actually need to regenerate anything
currentTime = time(NULL);
ENIntervalNumber currentInterval = en_get_interval_number(currentTime);
// we check if we need to generate new keys
if (currentInterval - periodInterval >= EN_TEK_ROLLING_PERIOD) {
periodInterval = en_get_interval_number_at_period_start(currentTime);
en_generate_and_derive_period_keys(&periodKey, &periodIdentifierKey, &periodMetadaEncryptionKey);
// TODO: Store new periodKey with periodInterval
}
// we now generate the new interval identifier and re-encrypt the metadata
ENIntervalIdentifier intervalIdentifier;
en_derive_interval_identifier(&intervalIdentifier, &periodIdentifierKey, currentInterval);
char encryptedMetadata[sizeof(metadata)];
en_encrypt_interval_metadata(&periodMetadaEncryptionKey, &intervalIdentifier, metadata, encryptedMetadata, sizeof(metadata));
// broadcast intervalIdentifier plus encryptedMetada according to specs
// TODO: receive packets and store them
// repeat for 10-20 minutes
}
return 0;
}

170
lib/exposure-notification/include/exposure-notification.h

@ -1,170 +0,0 @@
/*
* 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

14
lib/exposure-notification/library.json

@ -1,14 +0,0 @@
{
"description": "exposure-notification",
"frameworks": "*",
"keywords": "exposure, notification, contact, tracking, tracing",
"name": "exposure-notification",
"platforms": "*",
"version": "0.1",
"dependencies": [
{
"name": "mbedtls",
"version": "^2.16.4"
}
]
}

140
lib/exposure-notification/src/exposure-notification.c

@ -1,140 +0,0 @@
/*
* Copyright (c) 2020 Patrick Rathje
*
* SPDX-License-Identifier: Apache-2.0
*/
#if EN_INCLUDE_ZEPHYR_DEPS
#include <zephyr.h>
#include <zephyr/types.h>
#include <stddef.h>
#include <sys/printk.h>
#include <sys/util.h>
#endif
#include <string.h>
#include "mbedtls/entropy.h"
#include "mbedtls/ctr_drbg.h"
#include "mbedtls/hkdf.h"
#include "mbedtls/sha256.h"
#include "mbedtls/aes.h"
#include "exposure-notification.h"
static mbedtls_ctr_drbg_context ctr_drbg;
static ENRandomBytesCallback random_bytes_callback = NULL;
int en_mbedtls_random_bytes_fallback(void *buf, size_t len) {
return mbedtls_ctr_drbg_random(&ctr_drbg, buf, len);
}
#if EN_INIT_MBEDTLS_ENTROPY
int init_mbedtls_entropy() {
mbedtls_entropy_context entropy;
mbedtls_entropy_init( &entropy );
static char *personalization = "exposure-notification";
mbedtls_ctr_drbg_init( &ctr_drbg );
int ret = mbedtls_ctr_drbg_seed( &ctr_drbg , mbedtls_entropy_func, &entropy,
(const unsigned char *) personalization,
strlen( personalization ) );
return ret;
}
#endif
int en_init(ENRandomBytesCallback user_random_bytes_callback) {
int ret = 0;
#if EN_INIT_MBEDTLS_ENTROPY
ret = init_mbedtls_entropy();
#endif
// Fallback to mbedtls random bytes implementation and init the entropy
if (user_random_bytes_callback == NULL) {
random_bytes_callback = en_mbedtls_random_bytes_fallback;
} else {
random_bytes_callback = user_random_bytes_callback;
}
return ret;
}
ENIntervalNumber en_get_interval_number(time_t timestamp) {
return timestamp / EN_INTERVAL_LENGTH;
}
ENIntervalNumber en_get_interval_number_at_period_start(time_t timestamp) {
ENIntervalNumber current = en_get_interval_number(timestamp);
// round to period start
return (current/EN_TEK_ROLLING_PERIOD)*EN_TEK_ROLLING_PERIOD;
}
void en_generate_period_key(ENPeriodKey* periodKey) {
// TODO: error handling
random_bytes_callback(periodKey->b, sizeof(periodKey->b));
}
void en_derive_period_identifier_key(ENPeriodIdentifierKey *periodIdentifierKey, const ENPeriodKey *periodKey) {
const mbedtls_md_info_t *sha256_info = mbedtls_md_info_from_type(MBEDTLS_MD_SHA256);
// TODO: Include \0 in the string?
// TODO: Check return value
// TODO: Is this utf-8 info correct?
// TODO: Correct erros in en_get_period_metadata_encryption_key as well!
const unsigned char info[7] = "EN-RPIK";
mbedtls_hkdf(sha256_info, 0, 0, periodKey->b, sizeof(periodKey->b), info, sizeof(info), periodIdentifierKey->b, sizeof(periodIdentifierKey->b));
}
void en_derive_interval_identifier(ENIntervalIdentifier *intervalIdentifier, const ENPeriodIdentifierKey *periodIdentifierKey, const ENIntervalNumber intervalNumber) {
unsigned char paddedData[16] = "EN-RPI";
// copy intervalNumber in little endian format
paddedData[12] = (intervalNumber >> 0) &0xFF;
paddedData[13] = (intervalNumber >> 8) &0xFF;
paddedData[14] = (intervalNumber >> 16) &0xFF;
paddedData[15] = (intervalNumber >> 24) &0xFF;
mbedtls_aes_context aes;
mbedtls_aes_init( &aes );
// Encrypt the padded data to get the identifier
mbedtls_aes_setkey_enc( &aes, (const unsigned char*) periodIdentifierKey->b, sizeof(periodIdentifierKey->b) * 8 );
mbedtls_aes_crypt_ecb(&aes, MBEDTLS_AES_ENCRYPT, paddedData, intervalIdentifier->b);
mbedtls_aes_free( &aes );
}
void en_derive_period_metadata_encryption_key(ENPeriodMetadataEncryptionKey *periodMetadataEncryptionKey, const ENPeriodKey *periodKey) {
const mbedtls_md_info_t *sha256_info = mbedtls_md_info_from_type(MBEDTLS_MD_SHA256);
const unsigned char info[7] = "EN-AEMK";
mbedtls_hkdf(sha256_info, 0, 0, periodKey->b, sizeof(periodKey->b), info, sizeof(info), periodMetadataEncryptionKey->b, sizeof(periodMetadataEncryptionKey->b));
}
void en_encrypt_interval_metadata(const ENPeriodMetadataEncryptionKey *periodMetadataEncryptionKey, const ENIntervalIdentifier *intervalIdentifier, unsigned char *input, unsigned char *output, size_t inputSize) {
mbedtls_aes_context aes;
mbedtls_aes_init( &aes );
// Encrypt the padded data to get the identifier
size_t nonceOffset = 0;
unsigned char nonceCounter[16];
unsigned char streamBlock[16];
// init nonce/IV to intervalIdentifer
memcpy(nonceCounter, intervalIdentifier->b, sizeof(nonceCounter));
memset(streamBlock, 0, sizeof(streamBlock));
mbedtls_aes_setkey_enc( &aes, (const unsigned char*) periodMetadataEncryptionKey->b, sizeof(periodMetadataEncryptionKey->b) * 8 );
mbedtls_aes_crypt_ctr(&aes, inputSize, &nonceOffset, nonceCounter, streamBlock, input, output);
mbedtls_aes_free( &aes );
}
void en_decrypt_interval_metadata(const ENPeriodMetadataEncryptionKey *periodMetadataEncryptionKey, const ENIntervalIdentifier *intervalIdentifier, unsigned char *input, unsigned char *output, size_t inputSize) {
en_encrypt_interval_metadata(periodMetadataEncryptionKey, intervalIdentifier, input, output, inputSize);
}

8
platformio.ini

@ -22,14 +22,16 @@ build_flags =
# For testing: -DUNITY_EXCLUDE_SETJMP_H=1
-DEN_INCLUDE_ZEPHYR_DEPS=1
-DEN_INIT_MBEDTLS_ENTROPY=0
lib_deps = exposure-notification
lib_deps =
prathje/exposure-notification @ ^0.1
[env:desktop]
platform = native
test_ignore = test_embedded
lib_compat_mode = off
lib_deps = mbedtls@~2
lib_deps =
mbedtls@~2
prathje/exposure-notification @ ^0.1
build_flags =
-Iinclude/desktop
-Iinclude/tls_config

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