Cryptographic Key Pair Library for Linked Data _(crypto-ld)_


> A Javascript library for generating and performing common operations on Linked Data cryptographic key pairs.

Table of Contents

- Background
- Security
- Install
- Usage
- Contribute
- Commercial Support
- License

Background

See also (related specs):

* Linked Data Cryptographic Suite Registry
* Linked Data Proofs 1.0

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This library provides general Linked Data cryptographic key generation
functionality, but does not support any individual key type by default.

To use it, you must install individual driver libraries for each
cryptographic key type. The following libraries are currently supported.

| Type | Crypto Suite | Library | Usage |
|-------------|--------------|---------|-------|
| Ed25519 | Ed25519VerificationKey2020 (recommended), Ed25519VerificationKey2018 (legacy) | ed25519-verification-key-2020 >=1.0 (recommended), ed25519-verification-key-2018 >=2.0 (legacy) | Signatures, VCs, zCaps, DIDAuth |
| X25519/Curve25519 | X25519KeyAgreementKey2019 | x25519-key-agreement-key-2019 >=4.0 | ECDH key agreement, JWE/CWE encryption with minimal-cipher |
| Secp256k1 | EcdsaSecp256k1VerificationKey2019 | ecdsa-secp256k1-verification-key-2019 | Signatures, VCs, zCaps, DIDAuth, HD Wallets |

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For digital signatures using the
jsonld-signatures,
signing of Verifiable Credentials using vc-js,
authorization capabilities, and DIDAuth operations:

* Prefer Ed25519VerificationKey2020 type keys, by default.
* Use EcdsaSepc256k1 keys if your use case requires it (for example, if
you're developing for a Bitcoin-based or Ethereum-based ledger), or if you
require Hierarchical Deterministic (HD) wallet functionality.

For key agreement protocols for encryption operations:

* Use Curve25519 with the minimal-cipher
library.

Security

As with most security- and cryptography-related tools, the overall security of
your system will largely depend on your design decisions.

Install

- Node.js 14.0+ is required.

To install locally (for development):

``
git clone https://github.com/digitalcredentials/crypto-ld.git
cd crypto-ld
npm install
`

Usage

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In order to use this library, you will need to import and install driver
libraries for key types you'll be working with via the use() method.

To use the library with one or more supported suites:

`js
import {Ed25519VerificationKey2020} from '@digitalcredentials/ed25519-verification-key-2020';
import {X25519KeyAgreementKey2020} from '@digitalcredentials/x25519-key-agreement-key-2020';

import {CryptoLD} from '@digitalcredentials/crypto-ld';
const cryptoLd = new CryptoLD();

cryptoLd.use(Ed25519VerificationKey2020);
cryptoLd.use(X25519KeyAgreementKey2020);

const edKeyPair = await cryptoLd.generate({type: 'Ed25519VerificationKey2020'});
`

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To generate a new public/private key pair: cryptoLd.generate(options):

* {string} [type] Suite name, required.
* {string} [controller] Optional controller URI or DID to initialize the
generated key. (This will also init the key id.)
* {string} [seed] Optional deterministic seed value (only supported by some
key types, such as ed25519) from which to generate the key.

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To create an instance of a public/private key pair from data imported from
storage, use cryptoLd.from():

`js
const serializedKeyPair = { ... };

const keyPair = await cryptoLd.from(serializedKeyPair);
`

Note that only installed key types are supported, if you try to create a
key pair via from() for an unsupported type, an error will be thrown.

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The full range of operations will depend on key type. Here are some common
operations supported by all key types.

#### Exporting the public key only

To export just the public key of a pair - use export():

`js
keyPair.export({publicKey: true});
// ->
{
type: 'Ed25519VerificationKey2020',
id: 'did:example:1234#z6MkszZtxCmA2Ce4vUV132PCuLQmwnaDD5mw2L23fGNnsiX3',
controller: 'did:example:1234',
publicKeyMultibase: 'zEYJrMxWigf9boyeJMTRN4Ern8DJMoCXaLK77pzQmxVjf'
}
`

#### Exporting the full public-private key pair

To export the full key pair, including private key (warning: this should be a
carefully considered operation, best left to dedicated Key Management Systems):

`js
keyPair.export({publicKey: true, privateKey: true});
// ->
{
type: 'Ed25519VerificationKey2020',
id: 'did:example:1234#z6MkszZtxCmA2Ce4vUV132PCuLQmwnaDD5mw2L23fGNnsiX3',
controller: 'did:example:1234',
publicKeyMultibase: 'zEYJrMxWigf9boyeJMTRN4Ern8DJMoCXaLK77pzQmxVjf',
privateKeyMultibase: 'z4E7Q4neNHwv3pXUNzUjzc6TTYspqn9Aw6vakpRKpbVrCzwKWD4hQDHnxuhfrTaMjnR8BTp9NeUvJiwJoSUM6xHAZ'
}
`

#### Generating and verifying key fingerprint

To generate a fingerprint:

`js
keyPair.fingerprint();
// ->
'z6MkszZtxCmA2Ce4vUV132PCuLQmwnaDD5mw2L23fGNnsiX3'
`

To verify a fingerprint:

`js
keyPair.verifyFingerprint({
fingerprint: 'z6MkszZtxCmA2Ce4vUV132PCuLQmwnaDD5mw2L23fGNnsiX3'
});
// ->
{ valid: true }
`

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For key pairs that are related to signature and verification (that extend from
the LDVerifierKeyPair class), two additional operations must be supported:

#### Creating a signer function

In order to perform a cryptographic signature, you need to create a sign
function, and then invoke it.

`js
const keyPair = await cryptoLd.generate({type: 'Ed25519VerificationKey2020'});

const {sign} = keyPair.signer();

const data = 'test data to sign';
const signatureValue = await sign({data});
`

#### Creating a verifier function

In order to verify a cryptographic signature, you need to create a verify
function, and then invoke it (passing it the data to verify, and the signature).

`js
const keyPair = await cryptoLd.generate({type: 'Ed25519VerificationKey2020'});

const {verify} = keyPair.verifier();

const {valid} = await verify({data, signature});
``

Contribute

See the contribute file!

PRs accepted.

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