Minimal Cipher (minimal-cipher)
Minimal encryption/decryption JWE/CWE library, secure algs only, browser-compatible
Table of Contents
Security
TBD
Background
Every version of this library will only offer at most two algorithms for encryption/decryption: a recommended algorithm and a FIPS-compliant algorithm. The encryption API will expect the user to specify "recommended" or "fips" as the version of the algorithm to use, defaulting to "recommended".
In the event that the FIPS-compliant algorithm is the same as the recommended one in a given version of this library, then that particular version will use the same algorithm regardless of the user specified "version".
This version of the library will use "XChaCha20-Poly1305" as the "recommended" version and 256-bit "AES-GCM" as the FIPS-compliant version.
Note: XSalsa20-Poly1305 is an AE (Authenticated Encryption) algorithm, not
an AEAD (Authenticated Encryption and Associated Data) algorithm, making it
incompatible with the current requirements for a
JWE (JOSE Web Encryption)
protected
clear text header.
This library's API requires an interface for Key Encryption Key (KEKs). This enables key material that is protected from exfiltration to be used via HSM/SSM APIs, including Web KMS (TODO: citation needed).
Install
- Node.js 12+ required.
To install locally (for development):
git clone https://github.com/digitalbazaar/minimal-cipher.git
cd minimal-cipher
npm install
Usage
Pick a Cipher interface (recommended
or fips
) and create an instance:
const {Cipher} = require('minimal-cipher');
const cipher = new Cipher(); // by default {version: 'recommended'}
Encrypting
To encrypt something (to create a cipher, serialized as a JWE JSON document), you will need:
- Some data to encrypt (a string, an object, a stream)
- Keys (called Key Agreement Keys, or KAKs for short)
(You'll also need a keyResolver
, more about that later.)
First, assemble your Key Agreement public keys (you'll be encrypting with them, and the intended recipient will use the corresponding private keys to decrypt).
Put together a list of recipients
(essentially, you're listing the id
s of
public/private key pairs that will be used to encrypt/decrypt the message):
// Retrieve them from config, a ledger, registry or back channel
const keyAgreementKey = await fetchFromSomewhere();
// or derive them from an existing Ed25519 signing key
const X25519KeyPair = require('x25519-key-pair');
const {Ed25519KeyPair} = require('crypto-ld');
const edKeyPair = await Ed25519KeyPair.generate();
const keyAgreementKey = X25519KeyPair.fromEdKeyPair(edKeyPair);
// Don't forget to set your key's id. For example, DID + fingerprint
keyAgreementKey.id = `${did}#${keyAgreementKey.fingerprint()}`;
// or derive them from an authentication key extracted from DID Document
const didDoc = await veresDriver.get({did});
const authnKey = didDoc.getVerificationMethod({proofPurpose: 'authentication'});
const edKeyPair = await Ed25519KeyPair.from(authnKey);
const keyAgreementKey = X25519KeyPair.fromEdKeyPair(edKeyPair);
keyAgreementKey.id = authnKey.id;
const recipient = {
header: {
kid: keyAgreementKey.id,
alg: 'ECDH-ES+A256KW'
}
}
const recipients = [recipient];
You'll also need a keyResolver
. Notice that recipients
lists only key IDs,
not the keys themselves. A keyResolver
is a function that accepts a key ID
and resolves to the public key corresponding to it.
Some example resolvers:
// Basic hardcoded key resolver; you already have the key material
const publicKeyNode = {
'@context': 'https://w3id.org/security/v2',
id: keyAgreementKey.id,
type: 'X25519KeyAgreementKey2019',
publicKeyBase58: keyAgreementKey.publicKeyBase58
};
const keyResolver = async () => publicKeyNode;
// A more advanced resolver based on DID doc authentication keys
const keyResolver = async ({id}) => {
// Use veres driver to fetch the authn key directly
const authKeyPair = await Ed25519KeyPair.from(await veresDriver.get({did: id}));
// Convert authn key to key agreement key
return X25519KeyPair.fromEdKeyPair(authKeyPair);
}
// Using did-veres-one driver as a resolver for did:v1:nym: DID keys
// TODO: Implement this
// Using the did:key method driver as a key resolver
Create the JWE:
// To encrypt a string or a Uint8Array
const data = 'plain text';
const jweDoc = await cipher.encrypt({data, recipients, keyResolver});
// To encrypt an object
const obj = {key: 'value'};
const jweDoc = await cipher.encryptObject({obj, recipients, keyResolver});
Decrypting
Decrypt a JWE JSON Document, using a private keyAgreementKey
:
const data = await cipher.decrypt({jwe, keyAgreementKey});
const object = await cipher.decryptObject({jwe, keyAgreementKey});
TODO: Describe the required KEK API:
// id
, algorithm
, wrapKey({unwrappedKey})
, and unwrakKey({wrappedKey})
Contribute
See the contribute file!
PRs accepted.
Small note: If editing the README, please conform to the standard-readme specification.
Commercial Support
Commercial support for this library is available upon request from Digital Bazaar: support@digitalbazaar.com
License
New BSD License (3-clause) © Digital Bazaar