[PATCH 1/3] SSH client configuration: Use Protocol version 2 only

[PATCH 1/3] SSH client configuration: Use Protocol version 2 only

[Peter Müller]

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SSH Protocol version 1 is insecure and must not be used anymore.
Restrict SSH client configuration to ensure only version 2 is used.

Signed-off-by: Peter Müller <peter.mueller(a)link38.eu>
---
 config/ssh/ssh_config | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/config/ssh/ssh_config b/config/ssh/ssh_config
index 2abfae6d1..b36909f85 100644
--- a/config/ssh/ssh_config
+++ b/config/ssh/ssh_config
@@ -5,6 +5,9 @@ Host *
         # disable Roaming as it is known to be vulnerable
         UseRoaming no
 
+	# only use version 2 of SSH protocol
+	Protocol 2
+
         # only use secure crypto algorithm
         KexAlgorithms curve25519-sha256(a)libssh.org,diffie-hellman-group-exchange-sha256
         Ciphers chacha20-poly1305(a)openssh.com,aes256-gcm(a)openssh.com,aes128-gcm(a)openssh.com,aes256-ctr,aes192-ctr,aes128-ctr
-- 
2.16.4

[PATCH 2/3] SSH client configuration: Hash known_hosts entries

[Peter Müller]

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By default, entries in ~/.ssh/known_hosts disclosure on which servers a
user as access to, allowing detailled attack against these servers.
Depending on the affected infrastructure, this might be a privacy
problem, too.

Force SSH to hash new entries in known_hosts (existing ones will not be
converted) to avoid permission disclosure.

Signed-off-by: Peter Müller <peter.mueller(a)link38.eu>
---
 config/ssh/ssh_config | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/config/ssh/ssh_config b/config/ssh/ssh_config
index b36909f85..9f7121c76 100644
--- a/config/ssh/ssh_config
+++ b/config/ssh/ssh_config
@@ -33,4 +33,7 @@ Host *
         # ensure only allowed authentication methods are used
         PreferredAuthentications publickey,keyboard-interactive,password
 
+	# hash entries in ~/.ssh/known_hosts file to avoid permission disclosure
+	HashKnownHosts yes
+
 # EOF
-- 
2.16.4

[PATCH 3/3] SSH client configuration: Prefer server host keys in different order

[Peter Müller]

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SSH clients can set a preference for server host keys. To achive best
security and performance, ED25519 is preferred over ECDSA (also secure,
but a bit bigger and some of them use ECC curves from non-trustworthy
sources) which is preferred over RSA.

Since ED25519 keys are smaller and need less CPU time on both client and
server, this also achives a better performance.

Signed-off-by: Peter Müller <peter.mueller(a)link38.eu>
---
 config/ssh/ssh_config | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/config/ssh/ssh_config b/config/ssh/ssh_config
index 9f7121c76..462f2f1a0 100644
--- a/config/ssh/ssh_config
+++ b/config/ssh/ssh_config
@@ -36,4 +36,7 @@ Host *
 	# hash entries in ~/.ssh/known_hosts file to avoid permission disclosure
 	HashKnownHosts yes
 
+	# prefer server host keys in different order (ED25519, ECDSA, RSA)
+	HostKeyAlgorithms ssh-ed25519-cert-v01(a)openssh.com,ssh-ed25519,ecdsa-sha2-nistp256-cert-v01(a)openssh.com,ecdsa-sha2-nistp384-cert-v01(a)openssh.com,ecdsa-sha2-nistp521-cert-v01(a)openssh.com,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,rsa-sha2-512-cert-v01(a)openssh.com,rsa-sha2-256-cert-v01(a)openssh.com,rsa-sha2-512,rsa-sha2-256,ssh-rsa-cert-v01(a)openssh.com,ssh-rsa
+
 # EOF
-- 
2.16.4