add back GCM cipher

we originally removed GCM from the cipher chain due to vulnerabilities in OpenSSH. We are adding it back, since any sensible implementation will have had enough time to fix or backport. On top of that, GCM is generally a preferred algorithm. Let's get it back now.

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>

libraries/get_ssh_ciphers.rb

@@ -32,7 +32,7 @@ def self.get_ciphers(node, cbc_required)
         ciphers_53['weak'] = ciphers_53['default'] + ',aes256-cbc,aes192-cbc,aes128-cbc'
 
         ciphers_66 = {}
-        ciphers_66.default = 'chacha20-poly1305@openssh.com,aes256-ctr,aes192-ctr,aes128-ctr'
+        ciphers_66.default = 'chacha20-poly1305@openssh.com,aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes192-ctr,aes128-ctr'
         ciphers_66['weak'] = ciphers_66['default'] + ',aes256-cbc,aes192-cbc,aes128-cbc'
 
         # determine the cipher for the operating system