RHEL 7
RHEL 7.1 uses OpenSSH 6.6.1p1, including curve25519 and chacha20-poly1305.
HostKey /etc/ssh/ssh_host_ed25519_key
HostKey /etc/ssh/ssh_host_rsa_key
Ciphers chacha20-poly1305@openssh.com,aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes192-ctr,aes128-ctr
KexAlgorithms curve25519-sha256@libssh.org,diffie-hellman-group-exchange-sha256
MACs hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-ripemd160-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-512,hmac-sha2-256,hmac-ripemd160,umac-128@openssh.com
RHEL 6
RHEL 6 uses OpenSSH 5.3p1.
Ciphers aes256-ctr,aes192-ctr,aes128-ctr KexAlgorithms diffie-hellman-group-exchange-sha256 MACs hmac-sha2-512,hmac-sha2-256,hmac-ripemd160
Debian 8 / jessie
Debian 8 / jessie uses OpenSSH 6.7p1
Ciphers chacha20-poly1305@openssh.com,aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes192-ctr,aes128-ctr
KexAlgorithms curve25519-sha256@libssh.org,diffie-hellman-group-exchange-sha256
MACs hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-ripemd160-etm@ope
More way to harden SSL:
https://github.com/dev-sec/chef-ssh-hardening
https://github.com/stribika/stribika.github.io/wiki/Secure-Secure-Shell
