DataTrails This specification describes the COSE encoding of proofs for post- order traversal binary Merkle trees, also known as history trees and Merkle mountain ranges. Proving and verifying are defined in terms of the cryptographic asynchronous accumulator described by ReyzinYakoubov (https://eprint.iacr.org/2015/718.pdf). The technical advantages of post-order traversal binary Merkle trees are discussed in CrosbyWallachStorage (https://static.usenix.org/event/sec09/tech/full_papers/crosby.pdf) and PostOrderTlog (https://research.swtch.com/tlog#appendix_a).