libotp implements RFC4226 and RFC6238. These RFCs are implemented by Google's Google Authenticator.

OTP can increases the security for various things, such as web services, servers and even private computers.

A secret is shared between the client and a device. Passwords are generated based on the shared secret.

It is possible to work in two modes:

1. Counter based - The OTP is generated with a counter that is increased on each successful attempt.
2. Time based - The OTP is generated based on time. Codes are valid for a pre-configured amount of time.

• HTOP - HMAC One-Time-Password generation (RFC4226).
  • Configurable HMAC - SHA1, SHA256 or SHA512.
• TOTP - Time based One-Time-Password generation (RFC6238).
  • Configurable time step, RFC recommended is 30 seconds.
  • Configurable T0 (start time).