nRFEntropySource.cpp

00001 /* mbed Microcontroller Library
00002  * Copyright (c) 2006-2015 ARM Limited
00003  *
00004  * Licensed under the Apache License, Version 2.0 (the "License");
00005  * you may not use this file except in compliance with the License.
00006  * You may obtain a copy of the License at
00007  *
00008  *     http://www.apache.org/licenses/LICENSE-2.0
00009  *
00010  * Unless required by applicable law or agreed to in writing, software
00011  * distributed under the License is distributed on an "AS IS" BASIS,
00012  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
00013  * See the License for the specific language governing permissions and
00014  * limitations under the License.
00015  */
00016 #include "../EntropySource.h"
00017 
00018 #if defined(TARGET_NRF51822) || defined(TARGET_MCU_NRF52832) /* Persistent storage supported on nrf51 platforms */
00019 
00020 #include "nrf_soc.h"
00021 #include "nrf_error.h"
00022 #include "mbed.h"
00023 #include <mbedtls/entropy.h>
00024 
00025 /*
00026  * nRF51 has a TRNG that we can access using SoftDevice.
00027  */
00028 int eddystoneEntropyPoll(void *data, unsigned char *output, size_t len, size_t *olen)
00029 {
00030     uint8_t bytes_available = 0;
00031 
00032     // get the number of random bytes available
00033     if (sd_rand_application_bytes_available_get(&bytes_available) != NRF_SUCCESS) {
00034         return MBEDTLS_ERR_ENTROPY_SOURCE_FAILED;
00035     }
00036 
00037     // if there is more bytes available that what is requested,
00038     // truncate the number of bytes in output to len, otherwise use the total
00039     // of bytes available.
00040     const uint8_t output_len = bytes_available > len ? len : bytes_available;
00041 
00042     if (output_len) {
00043         // transfer "output_len" random bytes to output.
00044         if (sd_rand_application_vector_get(output, output_len) != NRF_SUCCESS) {
00045             return MBEDTLS_ERR_ENTROPY_SOURCE_FAILED;
00046         }
00047     }
00048 
00049     // Everything went fine, commit the output_len to the output parameter
00050     *olen = output_len;
00051     return 0;
00052 }
00053 
00054 int eddystoneRegisterEntropySource( mbedtls_entropy_context* ctx) {
00055     uint8_t pool_capacity;
00056     sd_rand_application_pool_capacity_get(&pool_capacity);
00057 
00058     return mbedtls_entropy_add_source(
00059         ctx,
00060         eddystoneEntropyPoll, // entropy source function
00061         NULL,                 // entropy source data, NULL in this case
00062         pool_capacity,        //  minimum number of bytes the entropy pool should wait on from this callback before releasing entropy
00063         MBEDTLS_ENTROPY_SOURCE_STRONG
00064     );
00065 }
00066 
00067 #endif /* #ifdef TARGET_NRF51822 */