Remove the "Decrypt empty buffer" test, as ChaCha20 is a stream cipher
and 0 bytes encrypted is identical to a 0 length buffer. The "ChaCha20
Encrypt and decrypt 0 bytes" test will test decryption of a 0 length
buffer.
Previously, even in the Chacha20 and Chacha20-Poly1305 tests, we would
test that decryption of an empty buffer would work with
MBEDTLS_CIPHER_AES_128_CBC.
Make the cipher used with the dec_empty_buf() test configurable, so that
Chacha20 and Chacha20-Poly1305 empty buffer tests can use ciphers other
than AES CBC. Then, make the Chacha20 and Chacha20-Poly1305 empty buffer
tests use the MBEDTLS_CIPHER_CHACHA20 and
MBEDTLS_CIPHER_CHACHA20_POLY1305 cipher suites.
This commit adds the command line option 'bad_cid' to the UDP proxy
`./programs/test/udp_proxy`. It takes a non-negative integral value N,
which if not 0 has the effect of duplicating every 1:N CID records
and modifying the CID in the first copy sent.
This is to exercise the stacks documented behaviour on receipt
of unexpected CIDs.
It is important to send the record with the unexpected CID first,
because otherwise the packet would be dropped already during
replay protection (the same holds for the implementation of the
existing 'bad_ad' option).
This commit modifies mbedtls_ssl_get_peer_cid() to also allow passing
NULL pointers in the arguments for the peer's CID value and length, in
case this information is needed.
For example, some users might only be interested in whether the use of
the CID was negotiated, in which case both CID value and length pointers
can be set to NULL. Other users might only be interested in confirming
that the use of CID was negotiated and the peer chose the empty CID,
in which case the CID value pointer only would be set to NULL.
It doesn't make sense to pass a NULL pointer for the CID length but a
non-NULL pointer for the CID value, as the caller has no way of telling
the length of the returned CID - and this case is therefore forbidden.
This commit modifies the CID configuration API mbedtls_ssl_conf_cid_len()
to allow the configuration of the stack's behaviour when receiving an
encrypted DTLS record with unexpected CID.
