In addition to making the APIs of the various AEAD modules more consistent
with each other, it's useful to have an auth_decrypt() function so that we can
safely check the tag ourselves, as the user might otherwise do it in an
insecure way (or even forget to do it altogether).
While the old name is explicit and aligned with the RFC, it's also very long,
so with the mbedtls_ prefix prepended we get a 31-char prefix to each
identifier, which quickly conflicts with our 80-column policy.
The new name is shorter, it's what a lot of people use when speaking about
that construction anyway, and hopefully should not introduce confusion at
it seems unlikely that variants other than 20/1305 be standardised in the
foreseeable future.
- in .h files: only put the context declaration inside the #ifdef _ALT
(this was changed in 2.9.0, ie after the original PR)
- in .c file: only leave selftest out of _ALT: even though some function are
trivial to build from other parts, alt implementors might want to go another
way about them (for efficiency or other reasons)
I refactored some code into the function mbedtls_constant_time_memcmp
in commit 7aad291 but this function is only used by GCM and
AEAD_ChaCha20_Poly1305 to check the tags. So this function is now
only enabled if either of these two ciphers is enabled.
This change permits users of the ChaCha20/Poly1305 algorithms
(and the AEAD construction thereof) to pass NULL pointers for
data that they do not need, and avoids the need to provide a valid
buffer for data that is not used.
This implementation is based off the description in RFC 7539.
The ChaCha20 code is also updated to provide a means of generating
keystream blocks with arbitrary counter values. This is used to
generated the one-time Poly1305 key in the AEAD construction.
We naturally added the new Curve448 ECP group ID in alphabetical order in
the mbedtls_ecp_group_id enum. However, this causes binary incompatibility
issues as previous binaries will use values for groups that now have a
different meaning. For example, MBEDTLS_ECP_DP_SECP192K1, old value 10,
would mean Curve448 (MBEDTLS_ECP_DP_CURVE448) and the wrong group ID used.
Fix the binary compatibility issue by adding new enum entries to the end of
the enum, even though this isn't so great for readbility as the list is no
longer in alphabetical order. However, the list wasn't perfectly in
alphabetical order before anyway.
