/**
* PSA API key derivation demonstration
*
* This program calculates a key ladder: a chain of secret material, each
* derived from the previous one in a deterministic way based on a label.
* Two keys are identical if and only if they are derived from the same key
* using the same label.
*
* The initial key is called the master key. The master key is normally
* randomly generated, but it could itself be derived from another key.
*
* This program derives a series of keys called intermediate keys.
* The first intermediate key is derived from the master key using the
* first label passed on the command line. Each subsequent intermediate
* key is derived from the previous one using the next label passed
* on the command line.
*
* This program has four modes of operation:
*
* - "generate": generate a random master key.
* - "wrap": derive a wrapping key from the last intermediate key,
* and use that key to encrypt-and-authenticate some data.
* - "unwrap": derive a wrapping key from the last intermediate key,
* and use that key to decrypt-and-authenticate some
* ciphertext created by wrap mode.
* - "save": save the last intermediate key so that it can be reused as
* the master key in another run of the program.
*
* See the usage() output for the command line usage. See the file
* `key_ladder_demo.sh` for an example run.
*/
/*
* Copyright The Mbed TLS Contributors
* SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
*/
/* First include Mbed TLS headers to get the Mbed TLS configuration and
* platform definitions that we'll use in this program. Also include
* standard C headers for functions we'll use here. */
#include "mbedtls/build_info.h"
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include "mbedtls/platform.h" // for mbedtls_setbuf
#include "mbedtls/platform_util.h" // for mbedtls_platform_zeroize
#include <psa/crypto.h>
/* If the build options we need are not enabled, compile a placeholder. */
#if !defined(PSA_WANT_ALG_SHA_256) || !defined(MBEDTLS_MD_C) || \
!defined(MBEDTLS_AES_C) || !defined(MBEDTLS_CCM_C) || \
!defined(MBEDTLS_PSA_CRYPTO_C) || !defined(MBEDTLS_FS_IO) || \
defined(MBEDTLS_PSA_CRYPTO_KEY_ID_ENCODES_OWNER)
int main(void)
{
printf("PSA_WANT_ALG_SHA_256 and/or MBEDTLS_MD_C and/or "
"MBEDTLS_AES_C and/or MBEDTLS_CCM_C and/or "
"MBEDTLS_PSA_CRYPTO_C and/or MBEDTLS_FS_IO "
"not defined and/or MBEDTLS_PSA_CRYPTO_KEY_ID_ENCODES_OWNER "
"defined.\n");
return 0;
}
#else
/* The real program starts here. */
/* Run a system function and bail out if it fails. */
#define SYS_CHECK(expr) \
do \
{ \
if (!(expr)) \
{ \
perror( #expr); \
status = DEMO_ERROR; \
goto exit; \
} \
} \
while (0)
/* Run a PSA function and bail out if it fails. */
#define PSA_CHECK(expr) \
do \
{ \
status = (expr); \
if (status != PSA_SUCCESS) \
{ \
printf("Error %d at line %d: %s\n", \
(int) status, \
__LINE__, \
#expr); \
goto exit; \
} \
} \
while (0)
/* To report operational errors in this program, use an error code that is
* different from every PSA error code. */
#define DEMO_ERROR 120
/* The maximum supported key ladder depth. */
#define MAX_LADDER_DEPTH 10
/* Salt to use when deriving an intermediate key. */
#define DERIVE_KEY_SALT ((uint8_t *) "key_ladder_demo.derive")
#define DERIVE_KEY_SALT_LENGTH (strlen((const char *) DERIVE_KEY_SALT))
/* Salt to use when deriving a wrapping key. */
#define WRAPPING_KEY_SALT ((uint8_t *) "key_ladder_demo.wrap")
#define WRAPPING_KEY_SALT_LENGTH (strlen((const char *) WRAPPING_KEY_SALT))
/* Size of the key derivation keys (applies both to the master key and
* to intermediate keys). */
#define KEY_SIZE_BYTES 40
/* Algorithm for key derivation. */
#define KDF_ALG PSA_ALG_HKDF(PSA_ALG_SHA_256)
/* Type and size of the key used to wrap data. */
#define WRAPPING_KEY_TYPE PSA_KEY_TYPE_AES
#define WRAPPING_KEY_BITS 128
/* Cipher mode used to wrap data. */
#define WRAPPING_ALG PSA_ALG_CCM
/* Nonce size used to wrap data. */
#define WRAPPING_IV_SIZE 13
/* Header used in files containing wrapped data. We'll save this header
* directly without worrying about data representation issues such as
* integer sizes and endianness, because the data is meant to be read
* back by the same program on the same machine. */
#define WRAPPED_DATA_MAGIC "key_ladder_demo" // including trailing null byte
#define WRAPPED_DATA_MAGIC_LENGTH (sizeof(WRAPPED_DATA_MAGIC))
typedef struct {
char magic[WRAPPED_DATA_MAGIC_LENGTH];
size_t ad_size; /* Size of the additional data, which is this header. */
size_t payload_size; /* Size of the encrypted data. */
/* Store the IV inside the additional data. It's convenient. */
uint8_t iv[WRAPPING_IV_SIZE];
} wrapped_data_header_t;
/* The modes that this program can operate in (see usage). */
enum program_mode {
MODE_GENERATE,
MODE_SAVE,
MODE_UNWRAP,
MODE_WRAP
};
/* Save a key to a file. In the real world, you may want to export a derived
* key sometimes, to share it with another party. */
static psa_status_t save_key(psa_key_id_t key,
const char *output_file_name)
{
psa_status_t status = PSA_SUCCESS;
uint8_t key_data[KEY_SIZE_BYTES];
size_t key_size;
FILE *key_file = NULL;
PSA_CHECK(psa_export_key(key,
key_data, sizeof(key_data),
&key_size));
SYS_CHECK((key_file = fopen(output_file_name, "wb")) != NULL);
/* Ensure no stdio buffering of secrets, as such buffers cannot be wiped. */
mbedtls_setbuf(key_file, NULL);
SYS_CHECK(fwrite(key_data, 1, key_size, key_file) == key_size);
SYS_CHECK(fclose(key_file) == 0);
key_file = NULL;
exit:
if (key_file != NULL) {
fclose(key_file);
}
return status;
}
/* Generate a master key for use in this demo.
*
* Normally a master key would be non-exportable. For the purpose of this
* demo, we want to save it to a file, to avoid relying on the keystore
* capability of the PSA crypto library. */
static psa_status_t generate(const char *key_file_name)
{
psa_status_t status = PSA_SUCCESS;
psa_key_id_t key = 0;
psa_key_attributes_t attributes = PSA_KEY_ATTRIBUTES_INIT;
psa_set_key_usage_flags(&attributes,
PSA_KEY_USAGE_DERIVE | PSA_KEY_USAGE_EXPORT);
psa_set_key_algorithm(&attributes, KDF_ALG);
psa_set_key_type(&attributes, PSA_KEY_TYPE_DERIVE);
psa_set_key_bits(&attributes, PSA_BYTES_TO_BITS(KEY_SIZE_BYTES));
PSA_CHECK(psa_generate_key(&attributes, &key));
PSA_CHECK(save_key(key, key_file_name));
exit:
(void) psa_destroy_key(key);
return status;
}
/* Load the master key from a file.
*
* In the real world, this master key would be stored in an internal memory
* and the storage would be managed by the keystore capability of the PSA
* crypto library. */
static psa_status_t import_key_from_file(psa_key_usage_t usage,
psa_algorithm_t alg,
const char *key_file_name,
psa_key_id_t *master_key)
{
psa_status_t status = PSA_SUCCESS;
psa_key_attributes_t attributes = PSA_KEY_ATTRIBUTES_INIT;
uint8_t key_data[KEY_SIZE_BYTES];
size_t key_size;
FILE *key_file = NULL;
unsigned char extra_byte;
SYS_CHECK((key_file = fopen(key_file_name, "rb")) != NULL);
/* Ensure no stdio buffering of secrets, as such buffers cannot be wiped. */
mbedtls_setbuf(key_file, NULL);
SYS_CHECK((key_size = fread(key_data, 1, sizeof(key_data),
key_file)) != 0);
if (fread(&extra_byte, 1, 1, key_file) != 0) {
printf("Key file too large (max: %u).\n",
(unsigned) sizeof(key_data));
status = DEMO_ERROR;
goto exit;
}
SYS_CHECK(fclose(key_file) == 0);
key_file = NULL;
psa_set_key_usage_flags(&attributes, usage);
psa_set_key_algorithm(&attributes, alg);
psa_set_key_type(&attributes, PSA_KEY_TYPE_DERIVE);
PSA_CHECK(psa_import_key(&attributes, key_data, key_size, master_key));
exit:
if (key_file != NULL) {
fclose(key_file);
}
mbedtls_platform_zeroize(key_data, sizeof(key_data));
if (status != PSA_SUCCESS) {
/* If the key creation hasn't happened yet or has failed,
* *master_key is null. psa_destroy_key( 0 ) is
* guaranteed to do nothing and return PSA_SUCCESS. */
(void) psa_destroy_key(*master_key);
*master_key = 0;
}
return status;
}
/* Derive the intermediate keys, using the list of labels provided on
* the command line. On input, *key is the master key identifier.
* This function destroys the master key. On successful output, *key
* is the identifier of the final derived key.
*/
static psa_status_t derive_key_ladder(const char *ladder[],
size_t ladder_depth,
psa_key_id_t *key)
{
psa_status_t status = PSA_SUCCESS;
psa_key_attributes_t attributes = PSA_KEY_ATTRIBUTES_INIT;
psa_key_derivation_operation_t operation = PSA_KEY_DERIVATION_OPERATION_INIT;
size_t i;
psa_set_key_usage_flags(&attributes,
PSA_KEY_USAGE_DERIVE | PSA_KEY_USAGE_EXPORT);
psa_set_key_algorithm(&attributes, KDF_ALG);
psa_set_key_type(&attributes, PSA_KEY_TYPE_DERIVE);
psa_set_key_bits(&attributes, PSA_BYTES_TO_BITS(KEY_SIZE_BYTES));
/* For each label in turn, ... */
for (i = 0; i < ladder_depth; i++) {
/* Start deriving material from the master key (if i=0) or from
* the current intermediate key (if i>0). */
PSA_CHECK(psa_key_derivation_setup(&operation, KDF_ALG));
PSA_CHECK(psa_key_derivation_input_bytes(
&operation, PSA_KEY_DERIVATION_INPUT_SALT,
DERIVE_KEY_SALT, DERIVE_KEY_SALT_LENGTH));
PSA_CHECK(psa_key_derivation_input_key(
&operation, PSA_KEY_DERIVATION_INPUT_SECRET,
*key));
PSA_CHECK(psa_key_derivation_input_bytes(
&operation, PSA_KEY_DERIVATION_INPUT_INFO,
(uint8_t *) ladder[i], strlen(ladder[i])));
/* When the parent key is not the master key, destroy it,
* since it is no longer needed. */
PSA_CHECK(psa_destroy_key(*key));
*key = 0;
/* Derive the next intermediate key from the parent key. */
PSA_CHECK(psa_key_derivation_output_key(&attributes, &operation,
key));
PSA_CHECK(psa_key_derivation_abort(&operation));
}
exit:
psa_key_derivation_abort(&operation);
if (status != PSA_SUCCESS) {
psa_destroy_key(*key);
*key = 0;
}
return status;
}
/* Derive a wrapping key from the last intermediate key. */
static psa_status_t derive_wrapping_key(psa_key_usage_t usage,
psa_key_id_t derived_key,
psa_key_id_t *wrapping_key)
{
psa_status_t status = PSA_SUCCESS;
psa_key_attributes_t attributes = PSA_KEY_ATTRIBUTES_INIT;
psa_key_derivation_operation_t operation = PSA_KEY_DERIVATION_OPERATION_INIT;
*wrapping_key = 0;
/* Set up a key derivation operation from the key derived from
* the master key. */
PSA_CHECK(psa_key_derivation_setup(&operation, KDF_ALG));
PSA_CHECK(psa_key_derivation_input_bytes(
&operation, PSA_KEY_DERIVATION_INPUT_SALT,
WRAPPING_KEY_SALT, WRAPPING_KEY_SALT_LENGTH));
PSA_CHECK(psa_key_derivation_input_key(
&operation, PSA_KEY_DERIVATION_INPUT_SECRET,
derived_key));
PSA_CHECK(psa_key_derivation_input_bytes(
&operation, PSA_KEY_DERIVATION_INPUT_INFO,
NULL, 0));
/* Create the wrapping key. */
psa_set_key_usage_flags(&attributes, usage);
psa_set_key_algorithm(&attributes, WRAPPING_ALG);
psa_set_key_type(&attributes, PSA_KEY_TYPE_AES);
psa_set_key_bits(&attributes, WRAPPING_KEY_BITS);
PSA_CHECK(psa_key_derivation_output_key(&attributes, &operation,
wrapping_key));
exit:
psa_key_derivation_abort(&operation);
return status;
}
static psa_status_t wrap_data(const char *input_file_name,
const char *output_file_name,
psa_key_id_t wrapping_key)
{
psa_status_t status;
FILE *input_file = NULL;
FILE *output_file = NULL;
psa_key_attributes_t attributes = PSA_KEY_ATTRIBUTES_INIT;
psa_key_type_t key_type;
long input_position;
size_t input_size;
size_t buffer_size = 0;
unsigned char *buffer = NULL;
size_t ciphertext_size;
wrapped_data_header_t header;
/* Find the size of the data to wrap. */
SYS_CHECK((input_file = fopen(input_file_name, "rb")) != NULL);
/* Ensure no stdio buffering of secrets, as such buffers cannot be wiped. */
mbedtls_setbuf(input_file, NULL);
SYS_CHECK(fseek(input_file, 0, SEEK_END) == 0);
SYS_CHECK((input_position = ftell(input_file)) != -1);
#if LONG_MAX > SIZE_MAX
if (input_position > SIZE_MAX) {
printf("Input file too large.\n");
status = DEMO_ERROR;
goto exit;
}
#endif
input_size = input_position;
PSA_CHECK(psa_get_key_attributes(wrapping_key, &attributes));
key_type = psa_get_key_type(&attributes);
buffer_size =
PSA_AEAD_ENCRYPT_OUTPUT_SIZE(key_type, WRAPPING_ALG, input_size);
/* Check for integer overflow. */
if (buffer_size < input_size) {
printf("Input file too large.\n");
status = DEMO_ERROR;
goto exit;
}
/* Load the data to wrap. */
SYS_CHECK(fseek(input_file, 0, SEEK_SET) == 0);
SYS_CHECK((buffer = calloc(1, buffer_size)) != NULL);
SYS_CHECK(fread(buffer, 1, input_size, input_file) == input_size);
SYS_CHECK(fclose(input_file) == 0);
input_file = NULL;
/* Construct a header. */
memcpy(&header.magic, WRAPPED_DATA_MAGIC, WRAPPED_DATA_MAGIC_LENGTH);
header.ad_size = sizeof(header);
header.payload_size = input_size;
/* Wrap the data. */
PSA_CHECK(psa_generate_random(header.iv, WRAPPING_IV_SIZE));
PSA_CHECK(psa_aead_encrypt(wrapping_key, WRAPPING_ALG,
header.iv, WRAPPING_IV_SIZE,
(uint8_t *) &header, sizeof(header),
buffer, input_size,
buffer, buffer_size,
&ciphertext_size));
/* Write the output. */
SYS_CHECK((output_file = fopen(output_file_name, "wb")) != NULL);
/* Ensure no stdio buffering of secrets, as such buffers cannot be wiped. */
mbedtls_setbuf(output_file, NULL);
SYS_CHECK(fwrite(&header, 1, sizeof(header),
output_file) == sizeof(header));
SYS_CHECK(fwrite(buffer, 1, ciphertext_size,
output_file) == ciphertext_size);
SYS_CHECK(fclose(output_file) == 0);
output_file = NULL;
exit:
if (input_file != NULL) {
fclose(input_file);
}
if (output_file != NULL) {
fclose(output_file);
}
if (buffer != NULL) {
mbedtls_platform_zeroize(buffer, buffer_size);
}
free(buffer);
return status;
}
static psa_status_t unwrap_data(const char *input_file_name,
const char *output_file_name,
psa_key_id_t wrapping_key)
{
psa_status_t status;
FILE *input_file = NULL;
FILE *output_file = NULL;
psa_key_attributes_t attributes = PSA_KEY_ATTRIBUTES_INIT;
psa_key_type_t key_type;
unsigned char *buffer = NULL;
size_t ciphertext_size = 0;
size_t plaintext_size;
wrapped_data_header_t header;
unsigned char extra_byte;
/* Load and validate the header. */
SYS_CHECK((input_file = fopen(input_file_name, "rb")) != NULL);
/* Ensure no stdio buffering of secrets, as such buffers cannot be wiped. */
mbedtls_setbuf(input_file, NULL);
SYS_CHECK(fread(&header, 1, sizeof(header),
input_file) == sizeof(header));
if (memcmp(&header.magic, WRAPPED_DATA_MAGIC,
WRAPPED_DATA_MAGIC_LENGTH) != 0) {
printf("The input does not start with a valid magic header.\n");
status = DEMO_ERROR;
goto exit;
}
if (header.ad_size != sizeof(header)) {
printf("The header size is not correct.\n");
status = DEMO_ERROR;
goto exit;
}
PSA_CHECK(psa_get_key_attributes(wrapping_key, &attributes));
key_type = psa_get_key_type(&attributes);
ciphertext_size =
PSA_AEAD_ENCRYPT_OUTPUT_SIZE(key_type, WRAPPING_ALG, header.payload_size);
/* Check for integer overflow. */
if (ciphertext_size < header.payload_size) {
printf("Input file too large.\n");
status = DEMO_ERROR;
goto exit;
}
/* Load the payload data. */
SYS_CHECK((buffer = calloc(1, ciphertext_size)) != NULL);
SYS_CHECK(fread(buffer, 1, ciphertext_size,
input_file) == ciphertext_size);
if (fread(&extra_byte, 1, 1, input_file) != 0) {
printf("Extra garbage after ciphertext\n");
status = DEMO_ERROR;
goto exit;
}
SYS_CHECK(fclose(input_file) == 0);
input_file = NULL;
/* Unwrap the data. */
PSA_CHECK(psa_aead_decrypt(wrapping_key, WRAPPING_ALG,
header.iv, WRAPPING_IV_SIZE,
(uint8_t *) &header, sizeof(header),
buffer, ciphertext_size,
buffer, ciphertext_size,
&plaintext_size));
if (plaintext_size != header.payload_size) {
printf("Incorrect payload size in the header.\n");
status = DEMO_ERROR;
goto exit;
}
/* Write the output. */
SYS_CHECK((output_file = fopen(output_file_name, "wb")) != NULL);
/* Ensure no stdio buffering of secrets, as such buffers cannot be wiped. */
mbedtls_setbuf(output_file, NULL);
SYS_CHECK(fwrite(buffer, 1, plaintext_size,
output_file) == plaintext_size);
SYS_CHECK(fclose(output_file) == 0);
output_file = NULL;
exit:
if (input_file != NULL) {
fclose(input_file);
}
if (output_file != NULL) {
fclose(output_file);
}
if (buffer != NULL) {
mbedtls_platform_zeroize(buffer, ciphertext_size);
}
free(buffer);
return status;
}
static psa_status_t run(enum program_mode mode,
const char *key_file_name,
const char *ladder[], size_t ladder_depth,
const char *input_file_name,
const char *output_file_name)
{
psa_status_t status = PSA_SUCCESS;
psa_key_id_t derivation_key = 0;
psa_key_id_t wrapping_key = 0;
/* Initialize the PSA crypto library. */
PSA_CHECK(psa_crypto_init());
/* Generate mode is unlike the others. Generate the master key and exit. */
if (mode == MODE_GENERATE) {
return generate(key_file_name);
}
/* Read the master key. */
PSA_CHECK(import_key_from_file(PSA_KEY_USAGE_DERIVE | PSA_KEY_USAGE_EXPORT,
KDF_ALG,
key_file_name,
&derivation_key));
/* Calculate the derived key for this session. */
PSA_CHECK(derive_key_ladder(ladder, ladder_depth,
&derivation_key));
switch (mode) {
case MODE_SAVE:
PSA_CHECK(save_key(derivation_key, output_file_name));
break;
case MODE_UNWRAP:
PSA_CHECK(derive_wrapping_key(PSA_KEY_USAGE_DECRYPT,
derivation_key,
&wrapping_key));
PSA_CHECK(unwrap_data(input_file_name, output_file_name,
wrapping_key));
break;
case MODE_WRAP:
PSA_CHECK(derive_wrapping_key(PSA_KEY_USAGE_ENCRYPT,
derivation_key,
&wrapping_key));
PSA_CHECK(wrap_data(input_file_name, output_file_name,
wrapping_key));
break;
default:
/* Unreachable but some compilers don't realize it. */
break;
}
exit:
/* Destroy any remaining key. Deinitializing the crypto library would do
* this anyway since they are volatile keys, but explicitly destroying
* keys makes the code easier to reuse. */
(void) psa_destroy_key(derivation_key);
(void) psa_destroy_key(wrapping_key);
/* Deinitialize the PSA crypto library. */
mbedtls_psa_crypto_free();
return status;
}
static void usage(void)
{
printf("Usage: key_ladder_demo MODE [OPTION=VALUE]...\n");
printf("Demonstrate the usage of a key derivation ladder.\n");
printf("\n");
printf("Modes:\n");
printf(" generate Generate the master key\n");
printf(" save Save the derived key\n");
printf(" unwrap Unwrap (decrypt) input with the derived key\n");
printf(" wrap Wrap (encrypt) input with the derived key\n");
printf("\n");
printf("Options:\n");
printf(" input=FILENAME Input file (required for wrap/unwrap)\n");
printf(" master=FILENAME File containing the master key (default: master.key)\n");
printf(" output=FILENAME Output file (required for save/wrap/unwrap)\n");
printf(" label=TEXT Label for the key derivation.\n");
printf(" This may be repeated multiple times.\n");
printf(" To get the same key, you must use the same master key\n");
printf(" and the same sequence of labels.\n");
}
int main(int argc, char *argv[])
{
const char *key_file_name = "master.key";
const char *input_file_name = NULL;
const char *output_file_name = NULL;
const char *ladder[MAX_LADDER_DEPTH];
size_t ladder_depth = 0;
int i;
enum program_mode mode;
psa_status_t status;
if (argc <= 1 ||
strcmp(argv[1], "help") == 0 ||
strcmp(argv[1], "-help") == 0 ||
strcmp(argv[1], "--help") == 0) {
usage();
return EXIT_SUCCESS;
}
for (i = 2; i < argc; i++) {
char *q = strchr(argv[i], '=');
if (q == NULL) {
printf("Missing argument to option %s\n", argv[i]);
goto usage_failure;
}
*q = 0;
++q;
if (strcmp(argv[i], "input") == 0) {
input_file_name = q;
} else if (strcmp(argv[i], "label") == 0) {
if (ladder_depth == MAX_LADDER_DEPTH) {
printf("Maximum ladder depth %u exceeded.\n",
(unsigned) MAX_LADDER_DEPTH);
return EXIT_FAILURE;
}
ladder[ladder_depth] = q;
++ladder_depth;
} else if (strcmp(argv[i], "master") == 0) {
key_file_name = q;
} else if (strcmp(argv[i], "output") == 0) {
output_file_name = q;
} else {
printf("Unknown option: %s\n", argv[i]);
goto usage_failure;
}
}
if (strcmp(argv[1], "generate") == 0) {
mode = MODE_GENERATE;
} else if (strcmp(argv[1], "save") == 0) {
mode = MODE_SAVE;
} else if (strcmp(argv[1], "unwrap") == 0) {
mode = MODE_UNWRAP;
} else if (strcmp(argv[1], "wrap") == 0) {
mode = MODE_WRAP;
} else {
printf("Unknown action: %s\n", argv[1]);
goto usage_failure;
}
if (input_file_name == NULL &&
(mode == MODE_WRAP || mode == MODE_UNWRAP)) {
printf("Required argument missing: input\n");
return DEMO_ERROR;
}
if (output_file_name == NULL &&
(mode == MODE_SAVE || mode == MODE_WRAP || mode == MODE_UNWRAP)) {
printf("Required argument missing: output\n");
return DEMO_ERROR;
}
status = run(mode, key_file_name,
ladder, ladder_depth,
input_file_name, output_file_name);
return status == PSA_SUCCESS ?
EXIT_SUCCESS :
EXIT_FAILURE;
usage_failure:
usage();
return EXIT_FAILURE;
}
#endif /* PSA_WANT_ALG_SHA_256 && MBEDTLS_MD_C &&
MBEDTLS_AES_C && MBEDTLS_CCM_C &&
MBEDTLS_PSA_CRYPTO_C && MBEDTLS_FS_IO */