Make sure ssh is more secure and more customizable

defaults/main.yml

@@ -13,6 +13,12 @@ sshd_default_allowed_groups:
 # Enable AllowUsers and AllowGroups options
 restrict_allow_users: True
 
+# Require ed25519 key
+only_allow_ed25519: true 
+
 # Allow login with password?
 sshd_password_authentication: 'no' # 'yes' or 'no'
- 
+
+# Allow optional cryptho methods (NOT RECOMENDED)
+generate_ecdsa_too: false
+use_diffie-hellman-group-exchange-sha256: false

tasks/main.yml

@@ -29,6 +29,15 @@
   notify:
     - restart ssh
 
+- name: Generate new ecdsa ssh host key pair if necessary
+  become: yes
+  command: ssh-keygen -t ecdsa -f 'ssh_host_ecdsa_key' -P '' -q
+  args:
+    chdir: '/etc/ssh/'
+    creates: 'ssh_host_ecdsa_key.pub'
+  notify:
+    - restart ssh
+  when: generate_ecdsa_too
 
 - name: Generate new ed25519 ssh host key pair if necessary
   become: yes
@@ -39,6 +48,18 @@
   notify:
     - restart ssh
 
+- name: Remove unwanted host keys
+  become: yes
+  file:
+    path: '/etc/ssh/ssh_host_{{ item }}_key'
+    state: absent
+  with_items:
+    - rsa
+    - dsa
+  notify:
+    - restart ssh
+  when: generate_ecdsa_too 
+
 - name: Remove unwanted host keys
   become: yes
   file:
@@ -50,6 +71,7 @@
     - dsa
   notify:
     - restart ssh
+  when: generate_ecdsa_too == false
 
 - file:
     path: '/etc/ssh/ssh_host_{{ item }}_key.pub'
@@ -61,4 +83,15 @@
     - dsa
   notify:
     - restart ssh
+  when: generate_ecdsa_too == false
 
+- file:
+    path: '/etc/ssh/ssh_host_{{ item }}_key.pub'
+    state: absent
+  become: yes
+  with_items:
+    - rsa
+    - dsa
+  notify:
+    - restart ssh
+  when: generate_ecdsa_too

templates/sshd_config

@@ -10,13 +10,16 @@ TCPKeepAlive yes
 # Key exchange
 #KexAlgorithms curve25519-sha256@libssh.org,
 #              diffie-hellman-group-exchange-sha256
-KexAlgorithms curve25519-sha256@libssh.org
+KexAlgorithms curve25519-sha256@libssh.org{%
+if use_diffie-hellman-group-exchange-sha256 %},diffie-hellman-group-exchange-sha256{% endif %}
 
 
 # Server authentication
 Protocol 2
 HostKey /etc/ssh/ssh_host_ed25519_key
-
+{% if generate_ecdsa_too %}
+HostKey /etc/ssh/ssh_host_ecdsa_key
+{% endif %}
 # Not available in openssh 6.7
 # HostKeyAlgorithms ssh-ed25519-cert-v01@openssh.com,ssh-ed25519
 
@@ -43,7 +46,8 @@ LoginGraceTime 120
 StrictModes yes
 
 # Not available in openssh 6.7
-# PubkeyAcceptedKeyTypes ssh-ed25519-cert-v01@openssh.com,ssh-ed25519
+{% if only_allow_ed25519 == false %}# {%
+endif %}PubkeyAcceptedKeyTypes ssh-ed25519-cert-v01@openssh.com,ssh-ed25519
 
 
 # Symmetric ciphers