tree 6eafc5d1ea8733b4c31b9f81df0db38f93b65c30
parent 853f9bd65e80f00e939ed72052e5c2e117dcac5c
author Hanno Becker <hanno.becker@arm.com> 1596796205 +0100
committer Hanno Becker <hanno.becker@arm.com> 1599485650 +0100

Introduce public macro for maximum symmetric cipher key length

This commit introduces the public macro MBEDTLS_MAX_KEY_LENGTH,
which evaluates to an upper bound for the key lengths of all enabled
ciphers, in Bytes.

This is analogous to the already existing macros MBEDTLS_MAX_IV_LENGTH
and MBEDTLS_MAX_BLOCK_LENGTH, which provide upper bounds for the IV
and block length, respectively.

For now, MBEDTLS_MAX_KEY_LENGTH is 32 Bytes by default, and 64 in case
XTS is enabled. This is a strict overapproximation for some restricted
configurations. Ideally, the upper bound should be calculated exactly
and automatically from the list of enabled ciphers. The same applies
to the existing macros MBEDTLS_MAX_IV_LENGTH and MBEDTLS_MAX_BLOCK_LENGTH,
though, and is left for future work.

Signed-off-by: Hanno Becker <hanno.becker@arm.com>