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psa_generate_key: remove the bit-size sanity check

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In psa_generate_key_internal() for ECC keys, remove the check that the
bit-size according to Mbed TLS is equal to the requested bit-size.
This check was necessary back when the PSA API encoded curves and key
sizes independently, in order to reject combinations such as SECP256R1
with a 512-bit size. Since the curve encoding changed to specifying a
curve family and a size separately, the Mbed TLS curve id (grp_id) and
the curve data (curve_info) are now determined from the size, and
checking that (curve_info->bit_size == bits) is now only a redundant
sanity check.

This check is actually buggy, because PSA Crypto and Mbed TLS don't
have exactly the same notion of key size. PSA thinks Curve25519 is
255-bit and secp224k1 is 225-bit, but Mbed TLS thinks they're 256-bit
and 224-bit respectively. Removing the check allows key generation to
work for these curves.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2020-09-30 18:55:42 +02:00
parent 360e2c41d8
commit 2acbed387d
2 changed files with 3 additions and 2 deletions
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3
ChangeLog.d/psa_generate_key-curve25519.txt Normal file
View file

@ -0,0 +1,3 @@
Bugfix
* Fix psa_generate_key() returning an error when asked to generate
an ECC key pair on Curve25519 or secp244k1.

2
library/psa_crypto.c
View file

@ -6110,8 +6110,6 @@ static psa_status_t psa_generate_key_internal(
return( PSA_ERROR_NOT_SUPPORTED );
if( grp_id == MBEDTLS_ECP_DP_NONE || curve_info == NULL )
return( PSA_ERROR_NOT_SUPPORTED );
if( curve_info->bit_size != bits )
return( PSA_ERROR_INVALID_ARGUMENT );
mbedtls_ecp_keypair_init( &ecp );
ret = mbedtls_ecp_gen_key( grp_id, &ecp,
mbedtls_ctr_drbg_random,