Can the legacy HAVE_LIBGCRYPT_AEAD check be removed?

["Dr. Matthias St. Pierre" <Matthias.St.Pierre () ncp-e com>]

Hi all,

in wsgcrypt.h the libgcrypt version is checked to ensure that it supports AEAD ciphers:

        #if GCRYPT_VERSION_NUMBER >= 0x010600 /* 1.6.0 */
        /* Whether to provide support for authentication in addition to decryption. */
        #define HAVE_LIBGCRYPT_AEAD
        #endif

        (see [1])

Given the fact that libgcrypt 1.6.0 was released in 2013-12-16 (see [2]), I was wondering whether after such a long 
time it would be acceptable to simplify
all the conditional code depending on HAVE_LIBGCRYPT_AEAD by making GCRYPT_VERSION_NUMBER >= 0x010600 a requirement and 
removing  the
#else code parts.

The reason why I am asking is because the packet-isakmp dissector has some conditional code to emulate AES-GCM using 
AES-CTR in the absence
of HAVE_LIBGCRYPT_AEAD which I'd like to remove. I did some git history research and noticed that there were some 
recent commits in 2020 related
to fixing compilation without HAVE_LIBGCRYPT_AEAD  (see [3]). However, I'm not sure whether this was done deliberately 
to support libgcrypt < 1.6.0
or just out of habit because nobody considered the option of removing the legacy check.

Regards,
Matthias


[1] https://gitlab.com/wireshark/wireshark/-/blob/06ed6930dc602b5b3b1a79a176272c1846840f8f/wsutil/wsgcrypt.h#L32-35
[2] https://github.com/gpg/libgcrypt/blob/ccfa9f2c1427b40483984198c3df41f8057f69f8/NEWS#L673


[3] output of:

        for f in $(git grep -l HAVE_LIBGCRYPT_AEAD); do \
                git annotate $f | grep HAVE_LIBGCRYPT_AEAD; \
        done | awk '{print $1}' | sort | uniq | xargs git show --oneline --pretty=reference  --no-patch  | grep -w fix

03af5553eb (ssl-utils: fix compilation if not HAVE_LIBGCRYPT_AEAD., 2018-03-15)
151ee60555 (http3: fix build without support for AEAD cipher suites., 2020-08-10)
8c99f4de8d (QUIC: fix compilation without HAVE_LIBGCRYPT_AEAD, 2020-11-19)
90c3e7dead (QUIC: fix build error without LIBGCRYPT_AEAD, 2020-07-13)
e7642e162f (TLS: fix build error without LIBGCRYPT_AEAD, 2020-07-13)
e846d238d7 (QUIC: fix compile  without LIBGCRYPT_AEAD, 2020-08-10)

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