What are the differences between these AES ciphers? aes128-ctr
aes192-ctr
aes256-ctr
aes128-gcm@openssh.com
aes256-gcm@openssh.com


Mac Sierra recently deprecated blowfish, but I don't understand use-case differences of other ciphers. This is for testing a remote web project with X11Forwarding. I'm also curious about the last option,


chacha20-poly1305@openssh.com
CTR mode aims at confidentiality only; GCM additionally aims at integrity (catching attempts to forge or modify a message by one not holding the key, nor having some form of access to a device holding it).

The numbers 128, 192 and 256 are the key size in bits. 128 bits of key is secure enough for most purposes; 192 (or more) is enough for all purposes, except when there is a regulatory requirement for even more. AES192 (resp. AES256) is slower than AES128 by roughly 20% (resp. 40%).

Chacha20-Poly1305 is functionally comparable to AES128-GCM (giving confidentiality and integrity), but is easier to implement securely and efficiently, especially without AES support in hardware.