/**
* 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 (C) 2018, ARM Limited, All Rights Reserved
* SPDX-License-Identifier: Apache-2.0
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may
* not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* This file is part of mbed TLS (https://tls.mbed.org)
*/
/* 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. */
#if !defined(MBEDTLS_CONFIG_FILE)
#include "mbedtls/config.h"
#else
#include MBEDTLS_CONFIG_FILE
#endif
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include "mbedtls/platform_util.h" // for mbedtls_platform_zeroize
/* If the build options we need are not enabled, compile a placeholder. */
#if !defined(MBEDTLS_SHA256_C) || !defined(MBEDTLS_MD_C) || \
!defined(MBEDTLS_AES_C) || !defined(MBEDTLS_CCM_C) || \
!defined(MBEDTLS_PSA_CRYPTO_C) || !defined(MBEDTLS_FS_IO)
int main( void )
{
printf("MBEDTLS_SHA256_C 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.\n");
return( 0 );
}
#else
/* The real program starts here. */
#include <psa/crypto.h>
/* 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 %u: %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_handle_t key_handle,
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_handle,
key_data, sizeof( key_data ),
&key_size ) );
SYS_CHECK( ( key_file = fopen( output_file_name, "wb" ) ) != 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_handle_t key_handle = 0;
psa_key_policy_t policy = PSA_KEY_POLICY_INIT;
PSA_CHECK( psa_allocate_key( &key_handle ) );
psa_key_policy_set_usage( &policy,
PSA_KEY_USAGE_DERIVE | PSA_KEY_USAGE_EXPORT,
KDF_ALG );
PSA_CHECK( psa_set_key_policy( key_handle, &policy ) );
PSA_CHECK( psa_generate_key( key_handle,
PSA_KEY_TYPE_DERIVE,
PSA_BYTES_TO_BITS( KEY_SIZE_BYTES ),
NULL, 0 ) );
PSA_CHECK( save_key( key_handle, key_file_name ) );
exit:
(void) psa_destroy_key( key_handle );
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_handle_t *master_key_handle )
{
psa_status_t status = PSA_SUCCESS;
psa_key_policy_t policy = PSA_KEY_POLICY_INIT;
uint8_t key_data[KEY_SIZE_BYTES];
size_t key_size;
FILE *key_file = NULL;
unsigned char extra_byte;
*master_key_handle = 0;
SYS_CHECK( ( key_file = fopen( key_file_name, "rb" ) ) != 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_CHECK( psa_allocate_key( master_key_handle ) );
psa_key_policy_set_usage( &policy, usage, alg );
PSA_CHECK( psa_set_key_policy( *master_key_handle, &policy ) );
PSA_CHECK( psa_import_key( *master_key_handle,
PSA_KEY_TYPE_DERIVE,
key_data, key_size ) );
exit:
if( key_file != NULL )
fclose( key_file );
mbedtls_platform_zeroize( key_data, sizeof( key_data ) );
if( status != PSA_SUCCESS )
{
/* If psa_allocate_key hasn't been called yet or has failed,
* *master_key_handle is 0. psa_destroy_key(0) is guaranteed to do
* nothing and return PSA_ERROR_INVALID_HANDLE. */
(void) psa_destroy_key( *master_key_handle );
*master_key_handle = 0;
}
return( status );
}
/* Derive the intermediate keys, using the list of labels provided on
* the command line. On input, *key_handle is a handle to the master key.
* This function closes the master key. On successful output, *key_handle
* is a handle to the final derived key. */
static psa_status_t derive_key_ladder( const char *ladder[],
size_t ladder_depth,
psa_key_handle_t *key_handle )
{
psa_status_t status = PSA_SUCCESS;
psa_key_policy_t policy = PSA_KEY_POLICY_INIT;
psa_crypto_generator_t generator = PSA_CRYPTO_GENERATOR_INIT;
size_t i;
psa_key_policy_set_usage( &policy,
PSA_KEY_USAGE_DERIVE | PSA_KEY_USAGE_EXPORT,
KDF_ALG );
/* 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(
&generator,
*key_handle,
KDF_ALG,
DERIVE_KEY_SALT, DERIVE_KEY_SALT_LENGTH,
(uint8_t*) ladder[i], strlen( ladder[i] ),
KEY_SIZE_BYTES ) );
/* When the parent key is not the master key, destroy it,
* since it is no longer needed. */
PSA_CHECK( psa_close_key( *key_handle ) );
*key_handle = 0;
PSA_CHECK( psa_allocate_key( key_handle ) );
PSA_CHECK( psa_set_key_policy( *key_handle, &policy ) );
/* Use the generator obtained from the parent key to create
* the next intermediate key. */
PSA_CHECK( psa_generator_import_key(
*key_handle,
PSA_KEY_TYPE_DERIVE,
PSA_BYTES_TO_BITS( KEY_SIZE_BYTES ),
&generator ) );
PSA_CHECK( psa_generator_abort( &generator ) );
}
exit:
psa_generator_abort( &generator );
if( status != PSA_SUCCESS )
{
psa_close_key( *key_handle );
*key_handle = 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_handle_t derived_key_handle,
psa_key_handle_t *wrapping_key_handle )
{
psa_status_t status = PSA_SUCCESS;
psa_key_policy_t policy = PSA_KEY_POLICY_INIT;
psa_crypto_generator_t generator = PSA_CRYPTO_GENERATOR_INIT;
*wrapping_key_handle = 0;
PSA_CHECK( psa_allocate_key( wrapping_key_handle ) );
psa_key_policy_set_usage( &policy, usage, WRAPPING_ALG );
PSA_CHECK( psa_set_key_policy( *wrapping_key_handle, &policy ) );
PSA_CHECK( psa_key_derivation(
&generator,
derived_key_handle,
KDF_ALG,
WRAPPING_KEY_SALT, WRAPPING_KEY_SALT_LENGTH,
NULL, 0,
PSA_BITS_TO_BYTES( WRAPPING_KEY_BITS ) ) );
PSA_CHECK( psa_generator_import_key(
*wrapping_key_handle,
PSA_KEY_TYPE_AES,
WRAPPING_KEY_BITS,
&generator ) );
exit:
psa_generator_abort( &generator );
if( status != PSA_SUCCESS )
{
psa_close_key( *wrapping_key_handle );
*wrapping_key_handle = 0;
}
return( status );
}
static psa_status_t wrap_data( const char *input_file_name,
const char *output_file_name,
psa_key_handle_t wrapping_key_handle )
{
psa_status_t status;
FILE *input_file = NULL;
FILE *output_file = NULL;
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 );
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;
buffer_size = PSA_AEAD_ENCRYPT_OUTPUT_SIZE( 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_handle, 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 );
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_handle_t wrapping_key_handle )
{
psa_status_t status;
FILE *input_file = NULL;
FILE *output_file = NULL;
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 );
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;
}
ciphertext_size =
PSA_AEAD_ENCRYPT_OUTPUT_SIZE( 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_handle, 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 );
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_handle_t derivation_key_handle = 0;
psa_key_handle_t wrapping_key_handle = 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_handle ) );
/* Calculate the derived key for this session. */
PSA_CHECK( derive_key_ladder( ladder, ladder_depth,
&derivation_key_handle ) );
switch( mode )
{
case MODE_SAVE:
PSA_CHECK( save_key( derivation_key_handle, output_file_name ) );
break;
case MODE_UNWRAP:
PSA_CHECK( derive_wrapping_key( PSA_KEY_USAGE_DECRYPT,
derivation_key_handle,
&wrapping_key_handle ) );
PSA_CHECK( unwrap_data( input_file_name, output_file_name,
wrapping_key_handle ) );
break;
case MODE_WRAP:
PSA_CHECK( derive_wrapping_key( PSA_KEY_USAGE_ENCRYPT,
derivation_key_handle,
&wrapping_key_handle ) );
PSA_CHECK( wrap_data( input_file_name, output_file_name,
wrapping_key_handle ) );
break;
default:
/* Unreachable but some compilers don't realize it. */
break;
}
exit:
/* Close any remaining key. Deinitializing the crypto library would do
* this anyway, but explicitly closing handles makes the code easier
* to reuse. */
(void) psa_close_key( derivation_key_handle );
(void) psa_close_key( wrapping_key_handle );
/* 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" );
}
#if defined(MBEDTLS_CHECK_PARAMS)
#include "mbedtls/platform_util.h"
void mbedtls_param_failed( const char *failure_condition,
const char *file,
int line )
{
printf( "%s:%i: Input param failed - %s\n",
file, line, failure_condition );
exit( EXIT_FAILURE );
}
#endif
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 /* MBEDTLS_SHA256_C && MBEDTLS_MD_C && MBEDTLS_AES_C && MBEDTLS_CCM_C && MBEDTLS_PSA_CRYPTO_C && MBEDTLS_FS_IO */