merkle-tree | Merkle Tree implementation in Java | Hashing library

merkle-tree is a Java library typically used in Security, Hashing applications. merkle-tree has no bugs, it has no vulnerabilities, it has build file available, it has a Permissive License and it has high support. You can download it from GitHub.

I recently hit upon the need to do checkpointing in a data processing system that has the requirement that no data event can ever be lost and no events can be processed and streamed out of order. I wanted a way to auto-detect this in production in real time. There are a couple of ways to do this, but since our data events already have a signature attached to them (a SHA1 hash), I decided that a useful way to do the checkpoint is basically keep a hash of hashes. One could do this with a hash list, where a chain of hashes for each data element is kept and when a checkpoint occurs the hash of all those hashes in order is taken. A disadvantage of this model is if the downstream system detects a hash mismatch (either due to a lost message or messages that are out-of-order) it would then have to iterate the full list to detect where the problem is. An elegant alternative is a hash tree, aka a Merkle Tree named after its inventor Ralph Merkle.