Geek alert – this post is largely for personal future reference on a geeky topic, how to set up private key authentication with the PuTTY terminal emulator program.

Other posts with instructions to use puttygen and where to put private/public key data are correct.  Google “putty ppk” for pointers to some of those.

The issue most posts on this topic don’t address is OS file permissions.  It seems that particularly on the CentOS servers I often work on, this is a sensitive issue.

The .ssh directory must be drwx——
The .ssh/authorized_keys file must be -rw——-
And particularly easy to miss, especially if you have reconfigured to make sharing easy among team members, your *home* directory must be drwxr-xr-x

That’s 700, 600, and 755 for the numeric chown crowd.