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PSA: implement key derivation for ECC keys

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Signed-off-by: Przemyslaw Stekiel <przemyslaw.stekiel@mobica.com>
This commit is contained in:
Przemyslaw Stekiel 2021-11-09 10:46:40 +01:00
parent 4579a972bf
commit 1608e33606
1 changed files with 98 additions and 12 deletions
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110
library/psa_crypto.c
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@ -4834,21 +4834,107 @@ static psa_status_t psa_generate_derived_key_internal(
size_t storage_size = bytes;
psa_status_t status;
if( ! key_type_is_raw_bytes( slot->attr.type ) )
return( PSA_ERROR_INVALID_ARGUMENT );
if( bits % 8 != 0 )
return( PSA_ERROR_INVALID_ARGUMENT );
data = mbedtls_calloc( 1, bytes );
if( data == NULL )
return( PSA_ERROR_INSUFFICIENT_MEMORY );
/*
* ECC key types require the generation of a private key which is an integer
* in the range [1, N - 1], where N is the boundary of the private key domain:
* N is the prime p for Diffie-Hellman, or the order of the
* curve’s base point for ECC.
*
* Let m be the bit size of N, such that 2^m > N >= 2^(m-1).
* This function generates the private key using the following process:
*
* 1. Draw a byte string of length ceiling(m/8) bytes.
* 2. If m is not a multiple of 8, set the most significant
* (8 * ceiling(m/8) - m) bits of the first byte in the string to zero.
* 3. Convert the string to integer k by decoding it as a big-endian byte string.
* 4. If k > N - 2, discard the result and return to step 1.
* 5. Output k + 1 as the private key.
*
* This method allows compliance to NIST standards
*/
if ( PSA_KEY_TYPE_IS_ECC( slot->attr.type ) )
{
int cmp_result;
do {
int ret;
psa_ecc_family_t curve = PSA_KEY_TYPE_ECC_GET_FAMILY(
slot->attr.type );
mbedtls_ecp_group_id grp_id =
mbedtls_ecc_group_of_psa( curve, bits, 0 );
status = psa_key_derivation_output_bytes( operation, data, bytes );
if( status != PSA_SUCCESS )
goto exit;
mbedtls_ecp_keypair ecp;
mbedtls_ecp_keypair_init( &ecp );
if( ( ret = mbedtls_ecp_group_load( &ecp.grp, grp_id ) ) != 0 )
return( ret );
/* N is the boundary of the private key domain */
mbedtls_mpi N = ecp.grp.N;
/* Let m be the bit size of N */
size_t m = ecp.grp.nbits;
size_t m_bytes = PSA_BITS_TO_BYTES( m );
/* Alloc buffer once */
if ( data == NULL )
data = mbedtls_calloc( 1, m_bytes );
if( data == NULL )
return( PSA_ERROR_INSUFFICIENT_MEMORY );
/* 1. Draw a byte string of length ceiling(m/8) bytes. */
status = psa_key_derivation_output_bytes( operation, data, m_bytes );
if( status != PSA_SUCCESS )
goto exit;
/* 2. If m is not a multiple of 8 */
if (m % 8)
{
/* set the most significant
* (8 * ceiling(m/8) - m) bits of the first byte in
* the string to zero.
*/
uint8_t clear_bit_count = ( 8 * m_bytes - m );
uint8_t clear_bit_mask = ( ( 1 << clear_bit_count ) - 1 );
clear_bit_mask = ~( clear_bit_mask << ( 8 - clear_bit_count ) );
data[0] = ( data[0] & clear_bit_mask );
}
/* 3. Convert the string to integer k by decoding it as a
* big-endian byte string.
*/
mbedtls_mpi k;
mbedtls_mpi_init( &k );
mbedtls_mpi_read_binary( &k, data, m_bytes);
/* 4. If k > N - 2, discard the result and return to step 1. */
mbedtls_mpi diff_N_2;
mbedtls_mpi_init( &diff_N_2 );
mbedtls_mpi_sub_int( &diff_N_2, &N, 2);
cmp_result = mbedtls_mpi_cmp_mpi( &k, &diff_N_2 );
/* 5. Output k + 1 as the private key. */
mbedtls_mpi sum_k_1;
mbedtls_mpi_init( &sum_k_1 );
mbedtls_mpi_add_int( &sum_k_1, &k, 1);
mbedtls_mpi_write_binary( &sum_k_1, data, m_bytes);
} while ( cmp_result == 1 );
} else {
if( ! key_type_is_raw_bytes( slot->attr.type ) )
return( PSA_ERROR_INVALID_ARGUMENT );
if( bits % 8 != 0 )
return( PSA_ERROR_INVALID_ARGUMENT );
data = mbedtls_calloc( 1, bytes );
if( data == NULL )
return( PSA_ERROR_INSUFFICIENT_MEMORY );
status = psa_key_derivation_output_bytes( operation, data, bytes );
if( status != PSA_SUCCESS )
goto exit;
#if defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_DES)
if( slot->attr.type == PSA_KEY_TYPE_DES )
psa_des_set_key_parity( data, bytes );
if( slot->attr.type == PSA_KEY_TYPE_DES )
psa_des_set_key_parity( data, bytes );
#endif /* MBEDTLS_PSA_BUILTIN_KEY_TYPE_DES */
}
slot->attr.bits = (psa_key_bits_t) bits;
psa_key_attributes_t attributes = {