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Make key agreement the secret input for key derivation

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* Documentation
* Proof-of-concept implementation
* Updates to the tests (work in progress)
This commit is contained in:
Gilles Peskine
2019-01-16 15:53:06 +01:00
parent 41ac513de8
commit 969c5d61f7
3 changed files with 131 additions and 79 deletions
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148
library/psa_crypto.c
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@ -3318,17 +3318,28 @@ exit:
#define HKDF_STATE_KEYED 2 /* got key */
#define HKDF_STATE_OUTPUT 3 /* output started */
static psa_algorithm_t psa_generator_get_kdf_alg(
const psa_crypto_generator_t *generator )
{
if ( PSA_ALG_IS_KEY_AGREEMENT( generator->alg ) )
return( PSA_ALG_KEY_AGREEMENT_GET_KDF( generator->alg ) );
else
return( generator->alg );
}
psa_status_t psa_generator_abort( psa_crypto_generator_t *generator )
{
psa_status_t status = PSA_SUCCESS;
if( generator->alg == 0 )
psa_algorithm_t kdf_alg = psa_generator_get_kdf_alg( generator );
if( kdf_alg == 0 )
{
/* The object has (apparently) been initialized but it is not
* in use. It's ok to call abort on such an object, and there's
* nothing to do. */
}
else
if( generator->alg == PSA_ALG_SELECT_RAW )
if( kdf_alg == PSA_ALG_SELECT_RAW )
{
if( generator->ctx.buffer.data != NULL )
{
@ -3339,14 +3350,14 @@ psa_status_t psa_generator_abort( psa_crypto_generator_t *generator )
}
else
#if defined(MBEDTLS_MD_C)
if( PSA_ALG_IS_HKDF( generator->alg ) )
if( PSA_ALG_IS_HKDF( kdf_alg ) )
{
mbedtls_free( generator->ctx.hkdf.info );
status = psa_hmac_abort_internal( &generator->ctx.hkdf.hmac );
}
else if( PSA_ALG_IS_TLS12_PRF( generator->alg ) ||
else if( PSA_ALG_IS_TLS12_PRF( kdf_alg ) ||
/* TLS-1.2 PSK-to-MS KDF uses the same generator as TLS-1.2 PRF */
PSA_ALG_IS_TLS12_PSK_TO_MS( generator->alg ) )
PSA_ALG_IS_TLS12_PSK_TO_MS( kdf_alg ) )
{
if( generator->ctx.tls12_prf.key != NULL )
{
@ -3617,6 +3628,7 @@ psa_status_t psa_generator_read( psa_crypto_generator_t *generator,
size_t output_length )
{
psa_status_t status;
psa_algorithm_t kdf_alg = psa_generator_get_kdf_alg( generator );
if( output_length > generator->capacity )
{
@ -3627,7 +3639,7 @@ psa_status_t psa_generator_read( psa_crypto_generator_t *generator,
goto exit;
}
if( output_length == 0 &&
generator->capacity == 0 && generator->alg == 0 )
generator->capacity == 0 && kdf_alg == 0 )
{
/* Edge case: this is a blank or finished generator, and 0
* bytes were requested. The right error in this case could
@ -3639,7 +3651,7 @@ psa_status_t psa_generator_read( psa_crypto_generator_t *generator,
}
generator->capacity -= output_length;
if( generator->alg == PSA_ALG_SELECT_RAW )
if( kdf_alg == PSA_ALG_SELECT_RAW )
{
/* Initially, the capacity of a selection generator is always
* the size of the buffer, i.e. `generator->ctx.buffer.size`,
@ -3657,17 +3669,17 @@ psa_status_t psa_generator_read( psa_crypto_generator_t *generator,
}
else
#if defined(MBEDTLS_MD_C)
if( PSA_ALG_IS_HKDF( generator->alg ) )
if( PSA_ALG_IS_HKDF( kdf_alg ) )
{
psa_algorithm_t hash_alg = PSA_ALG_HKDF_GET_HASH( generator->alg );
psa_algorithm_t hash_alg = PSA_ALG_HKDF_GET_HASH( kdf_alg );
status = psa_generator_hkdf_read( &generator->ctx.hkdf, hash_alg,
output, output_length );
}
else if( PSA_ALG_IS_TLS12_PRF( generator->alg ) ||
PSA_ALG_IS_TLS12_PSK_TO_MS( generator->alg ) )
else if( PSA_ALG_IS_TLS12_PRF( kdf_alg ) ||
PSA_ALG_IS_TLS12_PSK_TO_MS( kdf_alg ) )
{
status = psa_generator_tls12_prf_read( &generator->ctx.tls12_prf,
generator->alg, output,
kdf_alg, output,
output_length );
}
else
@ -4019,38 +4031,66 @@ psa_status_t psa_key_derivation( psa_crypto_generator_t *generator,
return( status );
}
psa_status_t psa_key_derivation_setup( psa_crypto_generator_t *generator,
psa_algorithm_t alg )
static psa_status_t psa_key_derivation_setup_kdf(
psa_crypto_generator_t *generator,
psa_algorithm_t kdf_alg )
{
if( generator->alg != 0 )
return( PSA_ERROR_BAD_STATE );
/* Make sure that alg is a supported key derivation algorithm.
* Key agreement algorithms and key selection algorithms are not
* supported by this function. */
/* Make sure that kdf_alg is a supported key derivation algorithm. */
#if defined(MBEDTLS_MD_C)
if( PSA_ALG_IS_HKDF( alg ) ||
PSA_ALG_IS_TLS12_PRF( alg ) ||
PSA_ALG_IS_TLS12_PSK_TO_MS( alg ) )
if( PSA_ALG_IS_HKDF( kdf_alg ) ||
PSA_ALG_IS_TLS12_PRF( kdf_alg ) ||
PSA_ALG_IS_TLS12_PSK_TO_MS( kdf_alg ) )
{
psa_algorithm_t hash_alg = PSA_ALG_HKDF_GET_HASH( alg );
psa_algorithm_t hash_alg = PSA_ALG_HKDF_GET_HASH( kdf_alg );
size_t hash_size = PSA_HASH_SIZE( hash_alg );
if( hash_size == 0 )
return( PSA_ERROR_NOT_SUPPORTED );
if( ( PSA_ALG_IS_TLS12_PRF( alg ) ||
PSA_ALG_IS_TLS12_PSK_TO_MS( alg ) ) &&
if( ( PSA_ALG_IS_TLS12_PRF( kdf_alg ) ||
PSA_ALG_IS_TLS12_PSK_TO_MS( kdf_alg ) ) &&
! ( hash_alg == PSA_ALG_SHA_256 && hash_alg == PSA_ALG_SHA_384 ) )
{
return( PSA_ERROR_NOT_SUPPORTED );
}
generator->capacity = 255 * hash_size;
return( PSA_SUCCESS );
}
#endif /* MBEDTLS_MD_C */
else if( PSA_ALG_IS_KEY_DERIVATION( alg ) )
else
return( PSA_ERROR_NOT_SUPPORTED );
}
psa_status_t psa_key_derivation_setup( psa_crypto_generator_t *generator,
psa_algorithm_t alg )
{
psa_status_t status;
if( generator->alg != 0 )
return( PSA_ERROR_BAD_STATE );
if( PSA_ALG_IS_KEY_AGREEMENT( alg ) )
{
psa_algorithm_t kdf_alg = PSA_ALG_KEY_AGREEMENT_GET_KDF( alg );
if( kdf_alg == PSA_ALG_SELECT_RAW )
{
/* It's too early to set the generator's capacity since it
* depends on the key size for the key agreement. */
status = PSA_SUCCESS;
}
else
{
status = psa_key_derivation_setup_kdf( generator, kdf_alg );
}
}
else if( PSA_ALG_IS_KEY_DERIVATION( alg ) )
{
status = psa_key_derivation_setup_kdf( generator, alg );
}
else
return( PSA_ERROR_INVALID_ARGUMENT );
generator->alg = alg;
return( PSA_SUCCESS );
if( status == PSA_SUCCESS )
generator->alg = alg;
return( status );
}
#if defined(MBEDTLS_MD_C)
@ -4135,27 +4175,40 @@ static psa_status_t psa_key_derivation_input_raw(
size_t data_length )
{
psa_status_t status;
psa_algorithm_t kdf_alg = psa_generator_get_kdf_alg( generator );
if( kdf_alg == PSA_ALG_SELECT_RAW )
{
if( generator->capacity != 0 )
return( PSA_ERROR_INVALID_ARGUMENT );
generator->ctx.buffer.data = mbedtls_calloc( 1, data_length );
if( generator->ctx.buffer.data == NULL )
return( PSA_ERROR_INSUFFICIENT_MEMORY );
memcpy( generator->ctx.buffer.data, data, data_length );
generator->ctx.buffer.size = data_length;
generator->capacity = data_length;
status = PSA_SUCCESS;
}
else
#if defined(MBEDTLS_MD_C)
if( PSA_ALG_IS_HKDF( generator->alg ) )
if( PSA_ALG_IS_HKDF( kdf_alg ) )
{
status = psa_hkdf_input( &generator->ctx.hkdf,
PSA_ALG_HKDF_GET_HASH( generator->alg ),
PSA_ALG_HKDF_GET_HASH( kdf_alg ),
step, data, data_length );
}
else
#endif /* MBEDTLS_MD_C */
#if defined(MBEDTLS_MD_C)
/* TLS-1.2 PRF and TLS-1.2 PSK-to-MS are very similar, so share code. */
else if( PSA_ALG_IS_TLS12_PRF( generator->alg ) ||
PSA_ALG_IS_TLS12_PSK_TO_MS( generator->alg ) )
if( PSA_ALG_IS_TLS12_PRF( kdf_alg ) ||
PSA_ALG_IS_TLS12_PSK_TO_MS( kdf_alg ) )
{
// TODO
status = PSA_ERROR_NOT_SUPPORTED;
}
else
#endif /* MBEDTLS_MD_C */
{
/* This can't happen unless the generator object was not initialized */
return( PSA_ERROR_BAD_STATE );
@ -4277,10 +4330,10 @@ exit:
* to potentially free embedded data structures and wipe confidential data.
*/
static psa_status_t psa_key_agreement_internal( psa_crypto_generator_t *generator,
psa_key_derivation_step_t step,
psa_key_slot_t *private_key,
const uint8_t *peer_key,
size_t peer_key_length,
psa_algorithm_t alg )
size_t peer_key_length )
{
psa_status_t status;
uint8_t shared_secret[PSA_KEY_AGREEMENT_MAX_SHARED_SECRET_SIZE];
@ -4288,7 +4341,7 @@ static psa_status_t psa_key_agreement_internal( psa_crypto_generator_t *generato
/* Step 1: run the secret agreement algorithm to generate the shared
* secret. */
switch( PSA_ALG_KEY_AGREEMENT_GET_BASE( alg ) )
switch( PSA_ALG_KEY_AGREEMENT_GET_BASE( generator->alg ) )
{
#if defined(MBEDTLS_ECDH_C)
case PSA_ALG_ECDH_BASE:
@ -4312,34 +4365,31 @@ static psa_status_t psa_key_agreement_internal( psa_crypto_generator_t *generato
/* Step 2: set up the key derivation to generate key material from
* the shared secret. */
status = psa_key_derivation_internal( generator,
shared_secret, shared_secret_length,
PSA_ALG_KEY_AGREEMENT_GET_KDF( alg ),
NULL, 0, NULL, 0,
PSA_GENERATOR_UNBRIDLED_CAPACITY );
status = psa_key_derivation_input_raw( generator, step,
shared_secret, shared_secret_length );
exit:
mbedtls_platform_zeroize( shared_secret, shared_secret_length );
return( status );
}
psa_status_t psa_key_agreement( psa_crypto_generator_t *generator,
psa_key_derivation_step_t step,
psa_key_handle_t private_key,
const uint8_t *peer_key,
size_t peer_key_length,
psa_algorithm_t alg )
size_t peer_key_length )
{
psa_key_slot_t *slot;
psa_status_t status;
if( ! PSA_ALG_IS_KEY_AGREEMENT( alg ) )
if( ! PSA_ALG_IS_KEY_AGREEMENT( generator->alg ) )
return( PSA_ERROR_INVALID_ARGUMENT );
status = psa_get_key_from_slot( private_key, &slot,
PSA_KEY_USAGE_DERIVE, alg );
PSA_KEY_USAGE_DERIVE, generator->alg );
if( status != PSA_SUCCESS )
return( status );
status = psa_key_agreement_internal( generator,
status = psa_key_agreement_internal( generator, step,
slot,
peer_key, peer_key_length,
alg );
peer_key, peer_key_length );
if( status != PSA_SUCCESS )
psa_generator_abort( generator );
return( status );