AES-GCM support

[malinoff]

It would be awesome to have this mode. It looks like it is present in

$ openssl version  
OpenSSL 1.0.1f 6 Jan 2014
$ openssl enc -help 2>&1 | grep gcm
-aes-128-ecb               -aes-128-gcm               -aes-128-ofb              
-aes-192-ecb               -aes-192-gcm               -aes-192-ofb              
-aes-256-ecb               -aes-256-gcm               -aes-256-ofb

[batterystaples]

While not entirely relevant, you should definitely upgrade OpenSSL. 1.0.1f has been affected by heartbleed. (See http://heartbleed.com/ for an explanation)

[malinoff]

@appleorange1 that machine does not use any TLS, but thanks for the reminder!

[malinoff]

@yann2192 any updates on this?

[yann2192]

@malinoff I think, aes-gcm isn't available on older openssl release.

I would prefer writing a clean loader for openssl stuff (see #11) and after add more curve or ciphers.

[malinoff]

@yann2192 If so, this cipher should be optional.