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