Setting a Cipher in .ssh/config (Client-Side)

To specify a cipher for an SSH connection in the client configuration file(~/.ssh/config), use the Ciphers directive.

Example: Setting a Preferred Cipher for a Specific Host:
Host remote-server
    Ciphers aes256-gcm@openssh.com,chacha20-poly1305@openssh.com

• This sets AES-256-GCM and ChaCha20-Poly1305 as preferred encryption algorithms for all servers with a wildcard.

To enforce a specific ciphers for all SSH connections, use:
Host *
    Ciphers aes256-gcm@openssh.com,chacha20-poly1305@openssh.com

To check which cipher is being used for an SSH connection, run:

ssh -vv user@remote-server | grep "cipher"

debug1: kex: algorithm: curve25519-sha256
debug1: cipher: aes256-gcm@openssh.com

• This shows the negotiated cipher and key exchange algorithm.