This repository contains the reference implementation that accompanies RFC 8391: "XMSS: eXtended Merkle Signature Scheme".

This reference implementation supports all parameter sets as defined in the RFC at run-time (specified by prefixing the public and private keys with a 32-bit oid). Implementations that want to use compile-time parameter sets can remove the struct xmss_params function parameter, and globally replace the use of its attributes by compile-time constants.

Please note that this reference implementation is intended for cross-validation and experimenting. Deploying cryptographic code in practice requires careful consideration of the specific deployment scenario and relevant threat model. This holds perhaps doubly so for stateful signature schemes such as XMSS.

When using the current code base, please be careful, expect changes and watch this document for further documentation. In particular, xmss_core_fast.c is long due for a serious clean-up. While this will not change its public API or output, it may affect the storage format of the BDS state (i.e. part of the secret key).

For the SHA-2 hash functions (i.e. SHA-256 and SHA-512), we rely on OpenSSL. Make sure to install the OpenSSL development headers. On Debian-based systems, this is achieved by installing the OpenSSL development package libssl-dev.

This reference implementation was written by Andreas Hülsing and Joost Rijneveld. All included code is available under the CC0 1.0 Universal Public Domain Dedication.