pam_skey —
S/Key PAM module
[service-name] module-type
  control-flag pam_skey
  [options]
The S/Key service module for PAM provides authentication
  services based on the S/Key One Time Password (OTP)
  authentication system.
The pam_skey module has no optional
    parameters.
  - /etc/skeykeys
- database of information for the S/Key system.