lthash

A Java implementation of LtHASH (Lattice Hash), a homomorphic hashing algorithm based on lattice cryptography introduced by Mihir Bellare and Daniele Micciancio in this paper. This is a simplified Java porting of the Facebook Folly C++ Library implementation of the algorithm introduced here.

Homomorphic Hashing

A homomorphic hash can simplistically be defined as a hash function such that one can compute the hash of a composite block from the hashes of the individual blocks or rather being f1 and f2 two hash functions and op1, op2 two operations it is true that:

$$f1(a op1 b) = f2(a) op2 f2(b)$$

One of the main building blocks of a homomorphic hashing function is therefore an underlying hash function (our f2).
This project depends on this Java implementation of the BLAKE2b cryptographic hash function.

Example

LtHash32 ltHash = new LtHash32();

// Create an initial checksum of the values in input
ltHash.add("apple".getBytes(), "orange".getBytes());
byte[] checksum = ltHash.getChecksum();

// Remove the hash of "apple" from the checksum and check
// if the 2 checksums are equals
ltHash.remove("apple".getBytes());
boolean isEqual = ltHash.checksumEquals(checksum);

// Update the hash of "orange" with the new value "apple"
// and check if the 2 checksums are equals
ltHash.update("orange".getBytes(), "apple".getBytes());
isEqual = ltHash.checksumEquals(checksum);

// Adding again the missing "orange" and check if the
// checksum has gotten back to the initial status
ltHash.add("orange".getBytes());
isEqual = ltHash.checksumEquals(checksum);