In case no user group ranking is set, all groups are now ranked equally
instead of the order in the `preferredGroup` array. This is the
behavior already indicated in the comment header of the function.
This change is necessary for applications that do not set their own
group ranking (via `wolfSSL_CTX_set_groups()` for example). When such an
application creates a TLS server and receives a ClientHello message with
multiple key shares, now the first key share is selected instead of the
one with the lowest index in the `preferredGroup` array.
Recent browsers with PQC support place two key shares in their
ClientHello message: a hybrid PQC + X25519 one and at least one
classic-only one. The hybrid one is the first one, indicating a
preference. Without this change, however, always the classic-only key
share has been selected, as these algorithms have a lower index in the
`preferredGroup` array compared to the PQC hybrids.
Tested using a patched version of NGINX.
This change also results in a different selection of a key share group
in case of a HelloRetryRequest message. For the tests, where static
ephemeral keys are used (`WOLFSSL_STATIC_EPHEMERAL`), an additional
check is necessary to make sure the correct key is used for the ECDH
calculation.
Signed-off-by: Tobias Frauenschläger <tobias.frauenschlaeger@oth-regensburg.de>
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