ssh-keygen: add key format conversion (#6213)

pages/common/ssh-keygen.md

@@ -8,19 +8,15 @@
 
 - Specify file in which to save the key:
 
-`ssh-keygen -f ~/.ssh/{{filename}}`
+`ssh-keygen -f {{~/.ssh/filename}}`
 
 - Generate an ed25519 key with 100 key derivation function rounds:
 
-`ssh-keygen -t ed25519 -a 100`
+`ssh-keygen -t {{ed25519}} -a {{100}}`
 
 - Generate an RSA 4096-bit key with email as a comment:
 
-`ssh-keygen -t rsa -b 4096 -C "{{email}}"`
-
-- Retrieve the key fingerprint from a host (useful for confirming the authenticity of the host when first connecting to it via SSH):
-
-`ssh-keygen -l -F {{remote_host}}`
+`ssh-keygen -t {{dsa|ecdsa|ed25519|rsa}} -b {{4096}} -C "{{comment|email}}"`
 
 - Remove the keys of a host from the known_hosts file (useful when a known host has a new key):
 
@@ -28,8 +24,12 @@
 
 - Retrieve the fingerprint of a key in MD5 Hex:
 
-`ssh-keygen -l -E md5 -f ~/.ssh/{{filename}}`
+`ssh-keygen -l -E {{md5}} -f {{~/.ssh/filename}}`
 
 - Change the password of a key:
 
-`ssh-keygen -p -f ~/.ssh/{{filename}}`
+`ssh-keygen -p -f {{~/.ssh/filename}}`
+
+- Change the type of the key format (for example from OPENSSH format to PEM), the file will be rewritten in-place:
+
+`ssh-keygen -p -N "" -m {{PEM}} -f {{~/.ssh/OpenSSH_private_key}}`