Precise Proofs

Read the introduction on Precise-Proofs

Precise-Proofs is a library for creating Merkle proofs out of protobuf messages. It handles flattening of objects, ordering the fields by label and creating shareable and independently verifiable proofs.

This library takes arbitrary protobuf messages and makes sure a Merkle tree can be reliable calculated from the values with each value representing a leaf in the tree.

{ 
    "Amount": "$1500",
    "InvoiceDate": "2018-03-01",
    "DueDate": "2018-08-01",
    "Country": "USA",
    "Supplier": "Arbor Tree Inc",
    "Buyer": "ACME Paper Inc",
    "Status": "APPROVED"
}

Above example would result in the following tree:

Proof format

This library defines a proof format that ensures both human readable, concise and secure Merkle proofs:

{  
    "property":"ValueA",
    "value":"Example",
    "salt":"1VWQFUGCXl1AYS0iAULHQow4XEjgJF/TpAuOO2Rnm+E=",
    "hashes":[  
        { "right":"kYXAGhDdPiFMq1ZQMOZiKmSf1S1eHNgJ6BIPSIExOj8=" },
        { "left":"GDgT7Km6NK6k4N/Id4CZXErL3p6clNX7sVnlNyegdG0=" },
        { "right":"qOZzS+YM8t1OfC87zEKgkKz6q0f3wwk5+ed+PR/2cDA=" }
    ]
}

There are a few things to note:

• When calculating the hash of the leaf, the dot notation of the property, the value and salt should be concatenated to produce the hash.
• The default proof expects values of documents to be salted to prevent rainbow table lookups.
• The value is included in the file as a string value not a native type.

Why protobuf?

Google's protobuf is a space efficient and fast format to serialize data in a portable way. It's easy to generate JSON out of

Usage:

See below code sample (examples/simple.go) for a usage example.

	// ExampleDocument is a protobuf message
	document := documentspb.ExampleDocument{
		Value1:      1,
		ValueA:      "Foo",
		ValueB:      "Bar",
		ValueBytes1: []byte("foobar"),
	}

	// The FillSalts method is a helper function that fills all fields with 32
	// random bytes. SaltedExampleDocument is a protobuf message that has the
	// same structure as ExampleDocument but has all `bytes` field types.
	salts := documentspb.SaltedExampleDocument{}
	FillSalts(&salts)

	doctree := NewDocumentTree()
	doctree.FillTree(&document, &salts)
	fmt.Printf("Generated tree: %s\n", doctree.String())
	// Output:
	// Generated tree: DocumentTree with Hash [k4E4F9xgvzDPtCGE0yM1QRguleSxQX6sZ14VTYAYVTk=] and [5] leaves
	
	proof, _ := doctree.CreateProof("ValueA")
	proofJson, _ := json.Marshal(proof)
	fmt.Println("Proof:\n", string(proofJson))
        // Output:
        // {"property":"ValueA","value":"Foo","salt":"YSJ0pFJ4fk0gYsCOU2zLC1xAcqSDcw7tdV4M5ydlCNw=","hashes":[{"right":"anfIr8Oa4PjWQsf2qFLIGgFBeBphTI+RGBaKp8F6Fw0="},{"left":"B+/DkYDB2vvYAuw9GTbVk7jpxM2vPddxsbhldM1wOus="},{"right":"hCkGp+gqakfRE1aLg4j4mA9eAvKn0LbulLOAKUVLSCg="}]}


	valid, _ := doctree.ValidateProof(&proof)
        // Output:
        // Proof validated: true

Missing features

The following features are being worked on:

• Support for nested documents
• Add support for more types, currently only timestamp.Timestamp, []byte, int64 and string types are supported