Today I did something stupid: I overwrote an SSH public key with a file from a different machine:

Obviously, I wanted to place the Public Key for the account from one machine on the other one to append it to the authorized_keys file of the target account. Unfortunately, I didn't bear in mind that I already had a public key file (id_rsa.pub) in this directory. So I had to re-create the Public Key file from the Private Key. This is quite easy, it appears that the SSH developers already thought of this situation. The following code will restore the Public Key file from the Private Key (example for an RSA key):