OpenSSH using private key on Windows (“Unprotected private key file” error)

You can use icacls in Windows instead of chmod to adjust file permission. To give the current user read permission and remove everything else (Which will allow openssh to work), this works nicely:

Command Prompt:

icacls .\private.key /inheritance:r
icacls .\private.key /grant:r "%username%":"(R)"

In PowerShell, you can get icacls to work by wrapping the command in a call to cmd.exe

icacls .\private.key /inheritance:r
start-process "icacls.exe" -ArgumentList '.\private.key /grant:r "$env:USERNAME":"(R)"'