From: Simon Ruderich <simon@ruderich.org>
Date: Sun, 5 Jan 2014 22:27:18 +0000 (+0100)
Subject: ssh_config: Use stronger algorithms.
X-Git-Url: https://ruderich.org/simon/gitweb/?p=config%2Fdotfiles.git;a=commitdiff_plain;h=8fab449d59c0cc250464c03d085625141b4b12a6

ssh_config: Use stronger algorithms.
---

diff --git a/ssh_config b/ssh_config
index 4f239be..2d27284 100644
--- a/ssh_config
+++ b/ssh_config
@@ -3,7 +3,7 @@
 # Some options are set even if they are default to prevent /etc/ssh/ssh_config
 # from overwriting them.
 
-# Copyright (C) 2011-2013  Simon Ruderich
+# Copyright (C) 2011-2014  Simon Ruderich
 #
 # This file is free software: you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -32,6 +32,32 @@ Host *
 # Force protocol version 2 which is more secure (default).
     Protocol 2
 
+# Use stronger algorithms. If some hosts require weaker versions then use Host
+# groups to enable them only for those specific machines.
+
+# Don't use SHA1 and disable elliptic curves whose security regarding the
+# parameters is still in debate.
+    KexAlgorithms diffie-hellman-group-exchange-sha256
+# Use stronger cipher versions. Disable CBC ciphers to prevent (unlikely)
+# plaintext recovery attack [1], disable RC4 because it's broken [2]; this
+# leaves only AES. No GCM ciphers yet because they are still very new.
+#
+# [1]: http://www.openssh.com/txt/cbc.adv
+# [2]: http://www.schneier.com/blog/archives/2013/03/new_rc4_attack.html
+    Ciphers aes256-ctr
+# Don't use weak MACs like MD5 or SHA1. However strong MACs are not as
+# important as strong ciphers because an attacker must be able to break a MAC
+# in real time to modify the data in transmit. Prefer "-etm" algorithms which
+# use encrypt-then-mac which is more secure than the default encrypt-and-mac
+# in SSH [1] (available since 6.2).
+#
+# [1]: http://cseweb.ucsd.edu/~mihir/papers/oem.html
+    MACs hmac-sha2-512-etm@openssh.com,hmac-sha2-512
+# Disable DSA host keys because they are weak (only 1024 bit) and elliptic
+# curves. I don't need certificates, therefore disables those algorithms as
+# well (*-cert-*).
+    HostKeyAlgorithms ssh-rsa
+
 # Disable X11 and agent forwarding for security reasons (defaults).
     ForwardX11 no
     ForwardAgent no