Added DTLS and ALPN client support.

[denandz]

This change adds support Datagram Transport Layer Security (DTLS) when creating UDP connections with ncat. Application-Layer Protocol Negotiation (ALPN) support has also been added, allowing the user to specify an ALPN string when connecting the SSL services. For example, connecting to an HTTP2 compatible web server and supplying the 'h2' ALPN string.

[dmiller-nmap]

@denandz Thanks for this contribution! It looks like a fun and exciting addition to our program. Before we can review it, please ensure that it passes our build test. Specifically, you should guard sections of code that depend on OpenSSL with #ifdef HAVE_OPENSSL.

[denandz]

@dmiller-nmap I double checked the code and it looks like all the relevant guards are there. The build test seems to have a problem locating DTLS_client_method(). What version of openssl is the build using? SSL_CTX_set_alpn_protos() is also only available in more recent versions of openssl. I guess I could attempt to get some voodoo working to detect the openssl version and add in additional guards? Please advise. Roger that, added in checks for the openssl version.

Also, in the travis-ci non-ssl builds are being built with openssl. The './configure $SSL_FLAG' doesn't seem to work as expected. On my system:

$ export SSL_FLAG="--without-ssl"
$ ./configure $SSL_FLAG
{snip}
Configured with: ndiff zenmap nping openssl lua ncat
Configured without: localdirs nmap-update
Type make (or gmake on some *BSD machines) to compile.
$

Similar is reflected in the travis-ci build logs. (EG: https://travis-ci.org/nmap/nmap/jobs/142393838)

[dmiller-nmap]

@denandz Thanks for pointing that out about the travis builds! I just pushed a change to correctly configure without OpenSSL. Hope to be able to review this pull soon.

[denandz]

@dmiller-nmap any update on the pull ?

[denandz]

McFly?

[denandz]

[denandz]

[denandz]

[dmiller-nmap]

Thanks again for this! Turns out we had a good deal of work to do to make it fit: found a bug in ciphersuite defaults, did a bit of refactoring, had to update the patch due to intermediate code changes, fixed up some tests that were failing on fast hardware, added documentation, added compile-time feature detection instead of version number checks (sorry I steered you wrong on that), etc. Commit incoming. If you want a different name credited in the changelog, let me know.

[denandz]

Thanks @dmiller-nmap! You can use Denis Andzakovic as the credit name in the change log. Thanks for merging these features ^_^