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Limit keys to 65528 bits

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65528 bits is more than any reasonable key until we start supporting
post-quantum cryptography.

This limit is chosen to allow bit-sizes to be stored in 16 bits, with
65535 left to indicate an invalid value. It's a whole number of bytes,
which facilitates some calculations, in particular allowing a key of
exactly PSA_CRYPTO_MAX_STORAGE_SIZE to be created but not one bit
more.

As a resource usage limit, this is arguably too large, but that's out
of scope of the current commit.

Test that key import, generation and derivation reject overly large
sizes.
This commit is contained in:
Gilles Peskine 2019-07-30 17:26:54 +02:00
parent 7e0cff90b9
commit c744d99386
7 changed files with 158 additions and 14 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

6
include/psa/crypto_struct.h
View file

@ -309,6 +309,12 @@ static inline struct psa_key_policy_s psa_key_policy_init( void )
return( v );
}
/* The maximum size of a key in bits.
* This is a whole number of bytes, to facilitate some calculations
* such as the maximum size of key data in storage.
*/
#define PSA_MAX_KEY_BITS 0xfff8
typedef struct
{
psa_key_type_t type;

16
library/psa_crypto.c
View file

@ -706,11 +706,14 @@ psa_status_t psa_import_key_into_slot( psa_key_slot_t *slot,
if( key_type_is_raw_bytes( slot->type ) )
{
/* Ensure that a bytes-to-bit conversion won't overflow. */
size_t bit_size = PSA_BYTES_TO_BITS( data_length );
/* Ensure that the bytes-to-bit conversion doesn't overflow. */
if( data_length > SIZE_MAX / 8 )
return( PSA_ERROR_NOT_SUPPORTED );
status = prepare_raw_data_slot( slot->type,
PSA_BYTES_TO_BITS( data_length ),
/* Ensure that the key is not overly large. */
if( bit_size > PSA_MAX_KEY_BITS )
return( PSA_ERROR_NOT_SUPPORTED );
status = prepare_raw_data_slot( slot->type, bit_size,
&slot->data.raw );
if( status != PSA_SUCCESS )
return( status );
@ -1470,6 +1473,13 @@ static psa_status_t psa_start_key_creation(
}
slot->type = attributes->core.type;
/* Refuse to create overly large keys.
* Note that this doesn't trigger on import if the attributes don't
* explicitly specify a size (so psa_get_key_bits returns 0), so
* psa_import_key() needs its own checks. */
if( psa_get_key_bits( attributes ) > PSA_MAX_KEY_BITS )
return( PSA_ERROR_NOT_SUPPORTED );
#if defined(MBEDTLS_PSA_CRYPTO_SE_C)
/* For a key in a secure element, we need to do three things:
* create the key file in internal storage, create the

11
library/psa_crypto_storage.h
View file

@ -35,9 +35,14 @@ extern "C" {
#include <stdint.h>
#include <string.h>
/* Limit the maximum key size to 30kB (just in case someone tries to
* inadvertently store an obscene amount of data) */
#define PSA_CRYPTO_MAX_STORAGE_SIZE ( 30 * 1024 )
/* Limit the maximum key size in storage. This should have no effect
* since the key size is limited in memory. */
#define PSA_CRYPTO_MAX_STORAGE_SIZE ( PSA_BITS_TO_BYTES( PSA_MAX_KEY_BITS ) )
/* Sanity check: a file size must fit in 32 bits. Allow a generous
* 64kB of metadata. */
#if PSA_CRYPTO_MAX_STORAGE_SIZE > 0xffff0000
#error PSA_CRYPTO_MAX_STORAGE_SIZE > 0xffff0000
#endif
/** The maximum permitted persistent slot number.
*

26
tests/suites/test_suite_psa_crypto.data
View file

@ -314,6 +314,14 @@ PSA import AES: bits=128 wrong
depends_on:MBEDTLS_AES_C
import:"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa":PSA_KEY_TYPE_AES:128:PSA_ERROR_INVALID_ARGUMENT
PSA import large key: raw, 65528 bits (ok)
depends_on:HAVE_RAM_AVAILABLE_128k
import_large_key:PSA_KEY_TYPE_RAW_DATA:8191:PSA_SUCCESS
PSA import large key: raw, 65536 bits (not supported)
depends_on:HAVE_RAM_AVAILABLE_128k
import_large_key:PSA_KEY_TYPE_RAW_DATA:8192:PSA_ERROR_NOT_SUPPORTED
PSA import RSA key pair: maximum size exceeded
depends_on:MBEDTLS_PK_PARSE_C:MBEDTLS_RSA_C
import_rsa_made_up:PSA_VENDOR_RSA_MAX_KEY_BITS+8:1:PSA_ERROR_NOT_SUPPORTED
@ -2075,6 +2083,17 @@ PSA key derivation: TLS 1.2 PRF SHA-256, derive key export, 1+41
depends_on:MBEDTLS_MD_C:MBEDTLS_SHA256_C:!PSA_PRE_1_0_KEY_DERIVATION
derive_key_export:PSA_ALG_TLS12_PRF(PSA_ALG_SHA_256):"0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b":"000102030405060708090a0b0c":"f0f1f2f3f4f5f6f7f8f9":1:41
# This test assumes that PSA_MAX_KEY_BITS (currently 65536-8 bits = 8191 bytes
# and not expected to be raised any time soon) is less than the maximum
# output from HKDF-SHA512 (255*64 = 16320 bytes).
PSA key derivation: largest possible key
depends_on:MBEDTLS_MD_C:MBEDTLS_SHA512_C:!PSA_PRE_1_0_KEY_DERIVATION
derive_large_key:PSA_ALG_HKDF(PSA_ALG_SHA_512):"0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b":"000102030405060708090a0b0c":"f0f1f2f3f4f5f6f7f8f9":PSA_MAX_KEY_BITS:PSA_SUCCESS
PSA key derivation: key too large
depends_on:MBEDTLS_MD_C:MBEDTLS_SHA512_C:!PSA_PRE_1_0_KEY_DERIVATION
derive_large_key:PSA_ALG_HKDF(PSA_ALG_SHA_512):"0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b":"000102030405060708090a0b0c":"f0f1f2f3f4f5f6f7f8f9":PSA_MAX_KEY_BITS + 1:PSA_ERROR_NOT_SUPPORTED
PSA key agreement setup: ECDH + HKDF-SHA-256: good
depends_on:MBEDTLS_PK_PARSE_C:MBEDTLS_ECP_C:MBEDTLS_ECP_DP_SECP256R1_ENABLED:MBEDTLS_ECDH_C:MBEDTLS_MD_C:MBEDTLS_SHA256_C
key_agreement_setup:PSA_ALG_KEY_AGREEMENT(PSA_ALG_ECDH, PSA_ALG_HKDF(PSA_ALG_SHA_256)):PSA_KEY_TYPE_ECC_KEY_PAIR(PSA_ECC_CURVE_SECP256R1):"c88f01f510d9ac3f70a292daa2316de544e9aab8afe84049c62a9c57862d1433":"04d12dfb5289c8d4f81208b70270398c342296970a0bccb74c736fc7554494bf6356fbf3ca366cc23e8157854c13c58d6aac23f046ada30f8353e74f33039872ab":PSA_SUCCESS
@ -2188,6 +2207,13 @@ generate_key:PSA_KEY_TYPE_RAW_DATA:7:PSA_KEY_USAGE_EXPORT:0:PSA_ERROR_INVALID_AR
PSA generate key: raw data, 8 bits
generate_key:PSA_KEY_TYPE_RAW_DATA:8:PSA_KEY_USAGE_EXPORT:0:PSA_SUCCESS
PSA generate key: raw data, 65528 bits (ok)
depends_on:HAVE_RAM_AVAILABLE_128k
generate_key:PSA_KEY_TYPE_RAW_DATA:8:PSA_KEY_USAGE_EXPORT:0:PSA_SUCCESS
PSA generate key: raw data, 65536 bits (not supported)
generate_key:PSA_KEY_TYPE_RAW_DATA:65536:PSA_KEY_USAGE_EXPORT:0:PSA_ERROR_NOT_SUPPORTED
PSA generate key: AES, 128 bits, CTR
depends_on:MBEDTLS_AES_C:MBEDTLS_CIPHER_MODE_CTR
generate_key:PSA_KEY_TYPE_AES:128:PSA_KEY_USAGE_EXPORT | PSA_KEY_USAGE_ENCRYPT | PSA_KEY_USAGE_DECRYPT:PSA_ALG_CTR:PSA_SUCCESS

100
tests/suites/test_suite_psa_crypto.function
View file

@ -7,6 +7,13 @@
#include "psa_crypto_helpers.h"
/* Tests that require more than 128kB of RAM plus change have this symbol
* as a dependency. Currently we always define this symbol, so the tests
* are always executed. In the future we should make this conditional
* so that tests that require a lot of memory are skipped on constrained
* platforms. */
#define HAVE_RAM_AVAILABLE_128k
/** An invalid export length that will never be set by psa_export_key(). */
static const size_t INVALID_EXPORT_LENGTH = ~0U;
@ -556,6 +563,7 @@ static int setup_key_derivation_wrap( psa_key_derivation_operation_t* operation,
TEST_ASSERT( ! "Key derivation algorithm not supported" );
}
if( capacity != SIZE_MAX )
PSA_ASSERT( psa_key_derivation_set_capacity( operation, capacity ) );
return( 1 );
@ -1237,6 +1245,54 @@ exit:
}
/* END_CASE */
/* BEGIN_CASE */
void import_large_key( int type_arg, int byte_size_arg,
int expected_status_arg )
{
psa_key_type_t type = type_arg;
size_t byte_size = byte_size_arg;
psa_key_attributes_t attributes = PSA_KEY_ATTRIBUTES_INIT;
psa_status_t expected_status = expected_status_arg;
psa_key_handle_t handle = 0;
psa_status_t status;
uint8_t *buffer = NULL;
size_t buffer_size = byte_size + 1;
size_t n;
/* It would be better to skip the test than fail it if the allocation
* fails, but the test framework doesn't support this yet. */
ASSERT_ALLOC( buffer, buffer_size );
memset( buffer, 'K', byte_size );
PSA_ASSERT( psa_crypto_init( ) );
/* Try importing the key */
psa_set_key_usage_flags( &attributes, PSA_KEY_USAGE_EXPORT );
psa_set_key_type( &attributes, type );
status = psa_import_key( &attributes, buffer, byte_size, &handle );
TEST_EQUAL( status, expected_status );
if( status == PSA_SUCCESS )
{
PSA_ASSERT( psa_get_key_attributes( handle, &attributes ) );
TEST_EQUAL( psa_get_key_type( &attributes ), type );
TEST_EQUAL( psa_get_key_bits( &attributes ),
PSA_BYTES_TO_BITS( byte_size ) );
memset( buffer, 0, byte_size + 1 );
PSA_ASSERT( psa_export_key( handle, buffer, byte_size, &n ) );
for( n = 0; n < byte_size; n++ )
TEST_EQUAL( buffer[n], 'K' );
for( n = byte_size; n < buffer_size; n++ )
TEST_EQUAL( buffer[n], 0 );
}
exit:
psa_destroy_key( handle );
PSA_DONE( );
mbedtls_free( buffer );
}
/* END_CASE */
/* BEGIN_CASE */
void import_rsa_made_up( int bits_arg, int keypair, int expected_status_arg )
{
@ -4563,6 +4619,50 @@ exit:
}
/* END_CASE */
/* BEGIN_CASE */
void derive_large_key( int alg_arg,
data_t *key_data, data_t *input1, data_t *input2,
int bits_arg,
int expected_status_arg )
{
psa_key_handle_t base_handle = 0;
psa_key_handle_t derived_handle = 0;
psa_algorithm_t alg = alg_arg;
size_t bits = bits_arg;
psa_status_t expected_status = expected_status_arg;
psa_key_derivation_operation_t operation = PSA_KEY_DERIVATION_OPERATION_INIT;
psa_key_attributes_t base_attributes = PSA_KEY_ATTRIBUTES_INIT;
psa_key_attributes_t derived_attributes = PSA_KEY_ATTRIBUTES_INIT;
PSA_ASSERT( psa_crypto_init( ) );
psa_set_key_usage_flags( &base_attributes, PSA_KEY_USAGE_DERIVE );
psa_set_key_algorithm( &base_attributes, alg );
psa_set_key_type( &base_attributes, PSA_KEY_TYPE_DERIVE );
PSA_ASSERT( psa_import_key( &base_attributes, key_data->x, key_data->len,
&base_handle ) );
if( !setup_key_derivation_wrap( &operation, base_handle, alg,
input1->x, input1->len,
input2->x, input2->len, SIZE_MAX ) )
goto exit;
psa_set_key_usage_flags( &derived_attributes, PSA_KEY_USAGE_EXPORT );
psa_set_key_algorithm( &derived_attributes, 0 );
psa_set_key_type( &derived_attributes, PSA_KEY_TYPE_RAW_DATA );
psa_set_key_bits( &derived_attributes, bits );
TEST_EQUAL( psa_key_derivation_output_key( &derived_attributes, &operation,
&derived_handle ),
expected_status );
exit:
psa_key_derivation_abort( &operation );
psa_destroy_key( base_handle );
psa_destroy_key( derived_handle );
PSA_DONE( );
}
/* END_CASE */
/* BEGIN_CASE */
void key_agreement_setup( int alg_arg,
int our_key_type_arg, data_t *our_key_data,

4
tests/suites/test_suite_psa_crypto_persistent_key.data
View file

@ -19,10 +19,10 @@ parse_storage_data_check:"505341004b4559":"":PSA_KEY_LIFETIME_PERSISTENT:PSA_KEY
# Not specific to files, but only run this test in an environment where the maximum size could be reached.
Save maximum size persistent raw key
depends_on:MBEDTLS_PSA_ITS_FILE_C
save_large_persistent_key:0:PSA_SUCCESS
save_large_persistent_key:PSA_CRYPTO_MAX_STORAGE_SIZE:PSA_SUCCESS
Save larger than maximum size persistent raw key, should fail
save_large_persistent_key:1:PSA_ERROR_INSUFFICIENT_STORAGE
save_large_persistent_key:PSA_CRYPTO_MAX_STORAGE_SIZE + 1:PSA_ERROR_NOT_SUPPORTED
Persistent key destroy
depends_on:MBEDTLS_PK_C:MBEDTLS_PK_PARSE_C:MBEDTLS_RSA_C

7
tests/suites/test_suite_psa_crypto_persistent_key.function
View file

@ -96,17 +96,14 @@ exit:
/* END_CASE */
/* BEGIN_CASE */
void save_large_persistent_key( int data_too_large, int expected_status )
void save_large_persistent_key( int data_length_arg, int expected_status )
{
psa_key_id_t key_id = 42;
psa_key_handle_t handle = 0;
uint8_t *data = NULL;
size_t data_length = PSA_CRYPTO_MAX_STORAGE_SIZE;
size_t data_length = data_length_arg;
psa_key_attributes_t attributes = PSA_KEY_ATTRIBUTES_INIT;
if( data_too_large )
data_length += 1;
ASSERT_ALLOC( data, data_length );
PSA_ASSERT( psa_crypto_init() );