From 98f14a3863aa34b492c8f2d984895f5d837260cd Mon Sep 17 00:00:00 2001 From: =?utf8?q?Peter=20M=C3=BCller?= Date: Sun, 28 Sep 2025 21:05:00 +0000 Subject: [PATCH] OpenSSH: Prefer AES-GCM ciphers over AES-CTR MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit This reflects the following change made upstream in OpenSSH 9.9: * ssh(1): prefer AES-GCM to AES-CTR mode when selecting a cipher for the connection. The default cipher preference list is now Chacha20/Poly1305, AES-GCM (128/256) followed by AES-CTR (128/192/256). However, we keep preferring AES-GCM over Chacha/Poly, as hardware acceleration often grants the former a better performance, while there is no security advance of Chacha/Poly usage over 256 bit AES-GCM. Signed-off-by: Peter Müller Signed-off-by: Michael Tremer --- config/ssh/ssh_config | 2 +- config/ssh/sshd_config | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/config/ssh/ssh_config b/config/ssh/ssh_config index d5f63f315c..a248001ff8 100644 --- a/config/ssh/ssh_config +++ b/config/ssh/ssh_config @@ -10,7 +10,7 @@ Host * # Only use secure crypto algorithms KexAlgorithms sntrup761x25519-sha512,sntrup761x25519-sha512@openssh.com,mlkem768x25519-sha256,curve25519-sha256,curve25519-sha256@libssh.org,diffie-hellman-group-exchange-sha256 - Ciphers aes256-gcm@openssh.com,aes256-ctr,chacha20-poly1305@openssh.com,aes192-ctr,aes128-gcm@openssh.com,aes128-ctr + Ciphers aes256-gcm@openssh.com,aes128-gcm@openssh.com,chacha20-poly1305@openssh.com,aes256-ctr,aes192-ctr,aes128-ctr MACs hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-512,hmac-sha2-256,umac-128@openssh.com # Always visualise server host keys (helps to identify key based MITM attacks) diff --git a/config/ssh/sshd_config b/config/ssh/sshd_config index 7b687457c8..25e5b18380 100644 --- a/config/ssh/sshd_config +++ b/config/ssh/sshd_config @@ -21,7 +21,7 @@ MaxStartups 5 # Only allow safe crypto algorithms KexAlgorithms sntrup761x25519-sha512,sntrup761x25519-sha512@openssh.com,mlkem768x25519-sha256,curve25519-sha256,curve25519-sha256@libssh.org,diffie-hellman-group-exchange-sha256 -Ciphers aes256-gcm@openssh.com,aes256-ctr,chacha20-poly1305@openssh.com,aes192-ctr,aes128-gcm@openssh.com,aes128-ctr +Ciphers aes256-gcm@openssh.com,aes128-gcm@openssh.com,chacha20-poly1305@openssh.com,aes256-ctr,aes192-ctr,aes128-ctr MACs hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-512,hmac-sha2-256,umac-128@openssh.com # Only allow cryptographically safe SSH host keys (adjust paths if needed) -- 2.47.3