How to create an SSH key pair in Linux/Mac/Windows(Cygwin/OpenSSH)

Warning: If your SSH private key is leaked, your account will be misused by the third-party. Please secure your private key with setting the passphrase.

SSH key pair creation method in Linux / Mac / Windows (Cygwin or OpenSSH) is as follows.
Please check man ssh-keygen command for key type difference.
There are correspondence / unsupported types depending on the version of openssh.

ecdsa key type:

$ ssh-keygen -t ecdsa

RSA key type:

$ ssh-keygen -t rsa

ed25519 key type:

$ ssh-keygen -t ed25519

When you execute one of the above commands, you will be asked for the save location as follows. If there is no particular preference, just press the Enter key.

Generating public/private keytype key pair.
Enter file in which to save the key $HOME/.ssh/id_keytype

Then you will be prompted for a passphrase, so enter it.
Enter passphrase (empty for no passphrase):

Re-enter your passphrase for confirmation.
Enter same passphrase again:

A key pair is output. The upper line shows the private key, and the lower line shows the public key. Register the public key in TSUBAME.
our identification has been saved in $HOME/.ssh/id_keytype
Your public key has been saved in $HOME/.ssh/id_keytype.pub.
The key fingerprint is:
SHA256:random number:username@hostname
The key's randomart image is:

Check the file with the following command.

$ ls ~/.ssh/ -l
drwx------  2 user group     512 Oct  6 10:50 .