node-merkle-tree

A JS Merkle Tree implementation, as used by keybase.

Install

``
npm install merkle-tree
`

And then

`javascript
var Base = require('merkle-tree').Base;
`

Testing

`
make test
`

All tests should pass.

API

This module is just a library, and for it to do anything useful, you'll have to subclass
the Base class required above. As an example, we provide a subclass of a Merkle-Tree
that lives in memory, which can be accessed as follows:

`javascript
var merkle_mod = require('merkle-tree');

// M = the number of children per interior node.
// N = the maximum number of leaves before a resplit.
var config = new merkle_mod.Config({ N : 4, M : 16 });
var myTree = new merkle_mod.MemTree(config);

// Keys are hashes expressed as hex strings.
var key = "961b6dd3ede3cb8ecbaacbd68de040cd78eb2ed5889130cceb4c49268ea4d506";
var value = { "foo" : 10 };

// We're just inserting one, but you can insert as many as you'd like.
myTree.upsert({'key' : key, 'value' : value}, function(err, new_root_hash) {
// Finding by default checks the hashes on all interior nodes down the tree.
// If you want to speed up your 'finds', then you can pass skip_verify : true
// to your find.
myTree.find({'key' : key, 'skip_verify' : false}, function(err, val2) {
assert.equal(value, val2);
});
});


// You can either build a tree one key/value pair at a time, as above, or
// you can build the whole thing at once.
var data = new merkle_mod.SortedMap({
"list": [
["aabbcc", "dog" ],
["ddccee", "cat" ],
["00aa33", "bird" ]
]
});
myTree.build({"sorted_map" : data }, function (err) {
console.log("done!");
});
`

To review, the Merkle Tree module provides the following classes:

- Config -- A configuration object that controls the shape of the tree.
- SortedMap -- A sorted map of key/value pairs that used for inputting a whole bunch of data at a time,
and is also used internally.
- Base -- A base, abstract tree implementation that needs to specialized.
- MemTree -- A speciailization of Base; all data lives in memory and disappears when the process ends.

The Base class has the following method calls:

- build({sortedMap}, cb) --- Build a tree from scratch using the given sorted map of data, and callback
when done.
- upsert({key,value,[txinfo]}, cb) --- Update or insert the given value at the given key. Provide optional
txinfo that is passed to the storage engine.
- find({key}, cb) --- Find the given key in the Merkle tree, starting from the root and going down.

How to Make an On-Disk Tree

The keybase server stores its Merkle tree on disk. It
implements the following methods of the Base class to do so:

- hash_fn(s) -- A function to hash an interior node into a key. Return the hex-string hash of the
given string. I'd just use SHA512: require('crypto').createHash('SHA512').update(s).digest('hex').
- store_node({key, obj, obj_s}, cb) --- Store the node value obj under the key key. For convenience,
you are also passed obj_s, the stringification of the object.
- lookup_node({key},cb) --- Read from disk the node whose key is key. Callback with the parsed
(not stringified) object
- lookup_root(cb) --- Should callback with the hash of the most recent tree root.
- commit_root({key,txinfo}, cb) --- Store the root hash to disk, optionally with the txinfo`
transaction info annotation.

For an example of how to do this, see the simple MemTree class.