This paper proposes and evaluates a new bipartite post-quantum digital signature protocol based on Winternitz chains and the HORS oracle. Mutually mistrustful Alice and Bob are able to agree and sign a series of documents in a way that makes it impossible (within the assumed security model) to repudiate their signatures. The number of signatures supported by a single public key is limited by a large number but the security of the signature scheme is not diminished by repeated application. A single public key supports both parties. Some ramifications are discussed, security parameters evaluated and an application area delineated for the proposed concept.