PSA: EC curve size macro #107

2019-05-13T13:27:41-05:00

gilles-peskine-arm commented

2019-05-13 13:27:41 -05:00

(Migrated from github.com)

New macro to get the bit size of an elliptic curve.

Fix a minor bug in private Weierstrass elliptic curve key import whereby a buffer that was too short was accepted and implicitly padded to the left with zeros.

New macro to get the bit size of an elliptic curve. Fix a minor bug in private Weierstrass elliptic curve key import whereby a buffer that was too short was accepted and implicitly padded to the left with zeros.

Patater (Migrated from github.com) reviewed

2019-05-15 07:06:50 -05:00

library/psa_crypto.c

					
				@ -622,2 +622,4 @@

				    mbedtls_ecp_group_id grp_id = mbedtls_ecc_group_of_psa( curve );

				    if( PSA_BITS_TO_BYTES( PSA_ECC_CURVE_BITS( curve ) ) != data_length )

				        return( PSA_ERROR_INVALID_ARGUMENT );

Do we support curves with bit sizes not even multiples of 8? Would we zero-pad within the first or last byte? I looked at export key format, but didn't see the answer, although we do mention endianness.

gilles-peskine-arm (Migrated from github.com) reviewed

2019-05-15 07:12:49 -05:00

library/psa_crypto.c

					
				@ -622,2 +622,4 @@

				    mbedtls_ecp_group_id grp_id = mbedtls_ecc_group_of_psa( curve );

				    if( PSA_BITS_TO_BYTES( PSA_ECC_CURVE_BITS( curve ) ) != data_length )

				        return( PSA_ERROR_INVALID_ARGUMENT );

Yes (P521). It's zero-padded in the most significant byte, which you know because the spec tells you you have to represent the number in a given number of bits. You know which byte that is because you're told the endianness.

gilles-peskine-arm commented

2019-05-15 17:19:55 -05:00

(Migrated from github.com)

I rebased the PR on top of the target branch. There was an undetected conflict: the test case added in this PR needed to be updated to match the change in the test function in the target branch.

yanesca (Migrated from github.com) approved these changes

2019-05-16 05:00:31 -05:00

yanesca (Migrated from github.com) left a comment

Looks good to me.

Patater commented

2019-05-16 05:59:30 -05:00

(Migrated from github.com)

CI failure is ABI job (known to fail until https://github.com/ARMmbed/mbedtls/pull/2636 lands in the development branch) and USE_PSA_CRYPTO, which doesn't work on the API branch.

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