This repo contains an implementation of "Merkle Hash Trees" (MHT). In cryptography and computer science, a hash tree or Merkle Hash Tree is a tree in which every "leaf" (node) is labelled with the cryptographic hash of a data block, and every node that is not a leaf (called a branch, inner node, or inode) is labelled with the cryptographic hash of the labels of its child nodes. Specifically, it implements the variant described in RFC6962

Assume that you have such an object, named data, and we'll look at how to use the MHT.

data = %w[a b c d e f g h i j k l m n o p q r s t u v w x y z]

We'll create a new MHT:

tree = Merkle::HashTree.new(data, Digest::SHA256)

The Merkle::HashTree constructor takes exactly two arguments: an object that implements the data access interface we'll talk about later, and a class (or object) which implements the same digest method signature as the core Digest::Base class. Typically, this will simply be a Digest subclass, such as Digest::MD5, Digest::SHA1, or (as in the example above) Digest::SHA256. This second argument is the way that the MHT calculates hashes in the tree -- it simply calls the #digest method on whatever you pass in as the second argument, passing in a string and expecting raw octets out the other end.

Once we have our MHT object, we can start to do things with it. For example, we can get the hash of the "head" of the tree:

tree.head_build   # => "<some long string of octets>"

We can also ask for a "consistency proof", we need to specify an index(n) of the last element of sub_tree (as a result sub_tree will be data[0...n]):

consistency_proof = tree.consistency_proof_build(10)   # => ["<hash>", "<hash>", ... ]

You can test it checking sum with hash head of the tree. Or use:

tree.consistency_proof_build_head(consistency_proof)   # => "<some long string of octets>"

There are also such things as "audit proofs", which you get by specifying a single leaf index:

audit_proof = tree.audit_proof_build(10)   # => [ { value: "<hash>", position: "left" }, { value: "<hash>", position: "right" }, ... ]

In this example, the audit proof will return a list of hashes that demonstrate that leaf 10 is in the tree and hasn't been removed or altered. You can test it checking sum with hash head of the tree. Or use:

tree.audit_proof_build_head(audit_proof, data[10])   # => "<some long string of octets>"

Contact me if you have any doubts or questions about this gem.

Email: tavrelkate@gmail.com Telegram: @tavrelkate