The hash-based signature scheme XMSS, specified in the Internet-Draft „XMSS: Extended Hash-Based Signatures“, has been implemented by Stefan-Lukas Gazdag (genua GmbH) and CYSEC researcher Denis Butin. Hash-based signatures are the first post-quantum signature scheme undergoing standardisation. The open source implementation closely follows the Internet-Draft, and is available on the squareUP project website.
The IRTF Internet-Draft can be found here:
The reference implementation (BSD licence) is available at