JSON Hash

This Deno¹ package contains several utilities to deal JSON data with cryptography. See the below sections for details.

canon.ts: JSON normalizer compliant with JCS

Cryptographic operations like hashing and signing need the data to be expressed in an invariant format so that the operations are reliably repeatable. Even if two messages are similar, only a single byte of difference causes totally different digests or signatures.

However, JSON allows stylistic freedom on their representations. For example, the following representations all encodes the same JSON entity:

{ "foo": "bar", "baz": [1, 2, 3] }
{ "baz": [1, 2, 3], "foo": "bar" }
{"foo":"bar","baz":[1,2,3]}
{ "\u0066\u006f\u006f": "\u0062\u0061\u0072", "\u0062\u0061\u007a": [1, 2, 3] }

In order to hash or sign JSON data, they should be normalized first. That’s why JSON Canonicalization Scheme (JCS) was proposed in RFC 8785. JCS allows only a single representation for each possible JSON entity. For example, the JSON entity the above multiple representations encode can be represented into only the below single form:

{"baz":[1,2,3],"foo":"bar"}

The canon.ts module implements JCS, which completely complies with RFC 8785. Here’s some example:

import { canonicalize } from "https://deno.land/x/json_hash/canon.ts";
import { assertEquals } from "https://deno.land/std/testing/asserts.ts";

assertEquals(
  canonicalize({ foo: "bar", baz: [1, 2, 3] }),
  canonicalize({
    "\x62\x61\x7a": [1, 2, 3],
    "\x66\x6f\x6f": "\x62\x61\x72",
  }),
);

digest.ts: Hashing JSON entities

This module is a thin wrapper around the above canonicalize() function and the curated collection of cryptographic hash algorithms:

import { digest } from "https://deno.land/x/json_hash/digest.ts";
import { toHex } from "https://deno.land/x/json_hash/hex.ts";

const data = { foo: "bar", baz: [ 1, 2, 3 ]};
const hash: Uint8Array = await digest("BLAKE3", data);
console.log(toHex(hash));
// dec9c1a89be824103c812b7ace381263335cd6f421a4d0f4dd407a4d3335189c

The digest() function guarantees that it will return the equivalent hash digest (in Uint8Array) for the same hash algorithm and the equivalent JSON entity. It means you don’t have to care about the order of how object keys occurs or how characters in string are encoded.

Also note that the above example uses BLAKE3, which is unsupported by Web Crypto API (as of January 2022). Powered by Deno’s std/crypto module, which is baked into Web Assembly, it provides much wider range of hash algorithms than Web Crypto API.

merkle.ts: Dealing JSON with Merkle tree

If you need to track changes of large JSON trees this module could help you. It provides merkle() function and MerkleHash<T> class which enables you to build Merkle trees.

Unlike digest() function from digest.ts module, merkle() function doesn’t digest the entire JSON data at once, but digests each small entity of the tree and digests them recursively. For example:

import { MerkleHash, merkle } from "https://deno.land/x/json_hash/merkle.ts";
import { assert } from "https://deno.land/std/testing/asserts.ts";

const a: MerkleHash<"BLAKE3"> = await merkle("BLAKE3", [1, 2, 3]);
const b: MerkleHash<"BLAKE3"> = await merkle("BLAKE3", [
  await merkle("BLAKE3", 1),
  await merkle("BLAKE3", 2),
  await merkle("BLAKE3", 3),
]);
assert(a.equals(b));

const c: MerkleHash<"BLAKE3"> = await merkle(
  "BLAKE3",
  { foo: "bar", baz: [1, 2, 3] }
);
const d: MerkleHash<"BLAKE3"> = await merkle(
  "BLAKE3",
  { foo: await merkle("BLAKE3", "bar"), baz: a }
);
assert(c.equals(d));

const e = await merkle(c);
assert(e.equals(c));

Note that merkle() returns MerkleHash<T> (instead of Uint8Array), and also takes a JSON tree mixed with MerkleHash<T> values. In this module, such mixed trees are called MerkleTree<T>.² The merkle() function behaves like below:

• merkle() derives MerkleHash<T> from MerkleTree<T>.
• merkle() makes no distinction between a MerkleTree<T> and MerkleHash<T> derived from the same tree.

In other words, the idea this module implements is very simple: hierarchical hash verification of JSON trees. If you still don’t get it well I recommend you to read Diving into Merkle Trees by Pedro Tavares.

mod.ts: Façade

This module re-exports everything in the above files.

See also Deno Doc for the complete API references.

Changelog

See CHANGES.md file.

License

Distributed under LGPL 3.0 or later.