Keypairs.js

Lightweight JavaScript RSA and ECDSA utils that work on Windows, Mac, and Linux using modern node.js APIs (no need for C compiler).

A thin wrapper around Eckles.js (ECDSA) and Rasha.js (RSA).

Features

• Generate keypairs
  • RSA
  • ECDSA (P-256, P-384)
• PEM-to-JWK (and SSH-to-JWK)
• JWK-to-PEM (and JWK-to-SSH)
• Create JWTs (and sign JWS)
• SHA256 JWK Thumbprints
• JWK fetching. See Keyfetch.js
  • OIDC
  • Auth0
• CLI
  • See keypairs-cli

Usage

A brief introduction to the APIs:

// generate a new keypair as jwk
// (defaults to EC P-256 when no options are specified)
Keypairs.generate().then(function (pair) {
  console.log(pair.private);
  console.log(pair.public);
});

// JWK to PEM
// (supports various 'format' and 'encoding' options)
return Keypairs.export({ jwk: pair.private, format: 'pkcs8' }).then(function (pem) {
  console.log(pem);
});

// PEM to JWK
return Keypairs.import({ pem: pem }).then(function (jwk) {
  console.log(jwk);
});

// Thumbprint a JWK (SHA256)
return Keypairs.thumbprint({ jwk: jwk }).then(function (thumb) {
  console.log(thumb);
});

// Sign a JWT (aka compact JWS)
return Keypairs.signJwt({
  jwk: pair.private
, iss: 'https://example.com'
, exp: '1h'
  // optional claims
, claims: {
  , sub: 'jon.doe@gmail.com'
  }
});

By default ECDSA keys will be used since they’ve had native support in node much longer than RSA has, and they’re smaller, and faster to generate.

API Overview

• generate (JWK)
• parse (PEM)
• parseOrGenerate (PEM to JWK)
• import (PEM-to-JWK)
• export (JWK-to-PEM, private or public)
• publish (Private JWK to Public JWK)
• thumbprint (JWK SHA256)
• signJwt
• signJws

Keypairs.generate(options)

Generates a public/private pair of JWKs as { private, public }

Option examples:

• RSA { kty: 'RSA', modulusLength: 2048 }
• ECDSA { kty: 'ECDSA', namedCurve: 'P-256' }

When no options are supplied EC P-256 (also known as prime256v1 and secp256r1) is used by default.

Keypairs.parse(options)

Parses either a JWK (encoded as JSON) or an x509 (encdode as PEM) and gives back the JWK representation.

Option Examples:

• JWK { key: ‘{ “kty”:“EC”, … }’ }
• PEM { key: ‘-----BEGIN PRIVATE KEY-----\n…’ }
• Public Key Only { key: ‘-----BEGIN PRIVATE KEY-----\n…‘, public: true }
• Must Have Private Key { key: ‘-----BEGIN PUBLIC KEY-----\n…‘, private: true }

Example:

Keypairs.parse({ key: '...' }).catch(function (e) {
  // could not be parsed or was a public key
  console.warn(e);
  return Keypairs.generate();
});

Keypairs.parseOrGenerate({ key, throw, [generate opts]… })

Parses the key. Logs a warning on failure, marches on. (a shortcut for the above, with private: true)

Option Examples:

• parse key if exist, otherwise generate { key: process.env["PRIVATE_KEY"] }
• generated key curve { key: null, namedCurve: 'P-256' }
• generated key modulus { key: null, modulusLength: 2048 }

Example:

Keypairs.parseOrGenerate({ key: process.env["PRIVATE_KEY"] }).then(function (pair) {
  console.log(pair.public);
})

Great for when you have a set of shared keys for development and randomly generated keys in

Keypairs.import({ pem: ‘…’ }

Takes a PEM in pretty much any format (PKCS1, SEC1, PKCS8, SPKI) and returns a JWK.

Keypairs.export(options)

Exports a JWK as a PEM.

Exports PEM in PKCS8 (private) or SPKI (public) by default.

Options

{ jwk: jwk
, public: true
, encoding: 'pem' // or 'der'
, format: 'pkcs8' // or 'ssh', 'pkcs1', 'sec1', 'spki'
}

Keypairs.publish({ jwk: jwk, exp: ‘3d’, use: ‘sig’ })

Promises a public key that adheres to the OIDC and Auth0 spec (plus expiry), suitable to be published to a JWKs URL:

{ "kty": "EC"
, "crv": "P-256"
, "x": "..."
, "y": "..."
, "kid": "..."
, "use": "sig"
, "exp": 1552074208
}

In particular this adds “use” and “exp”.

Keypairs.thumbprint({ jwk: jwk })

Promises a JWK-spec thumbprint: URL Base64-encoded sha256

Keypairs.signJwt({ jwk, header, claims })

Returns a JWT (otherwise known as a protected JWS in “compressed” format).

{ jwk: jwk
  // required claims
, iss: 'https://example.com'
, exp: '15m'
  // all optional claims
, claims: {
  }
}

Exp may be human readable duration (i.e. 1h, 15m, 30s) or a datetime in seconds.

Header defaults:

{ kid: thumbprint
, alg: 'xS256'
, typ: 'JWT'
}

Payload notes:

• iat: now is added by default (set false to disable)
• exp must be set (set false to disable)
• iss should be the base URL for JWK lookup (i.e. via OIDC, Auth0)

Notes:

header is actually the JWS protected value, as all JWTs use protected headers (yay!) and claims are really the JWS payload.

Keypairs.signJws({ jwk, header, protected, payload })

This is provided for APIs like ACME (Let’s Encrypt) that use uncompressed JWS (instead of JWT, which is compressed).

Options:

• header not what you think. Leave undefined unless you need this for the spec you’re following.
• protected is the typical JWT-style header
  • kid and alg will be added by default (these are almost always required), set false explicitly to disable
• payload can be JSON, a string, or even a buffer (which gets URL Base64 encoded)
  • you must set this to something, even if it’s an empty string, object, or Buffer

Additional Documentation

Keypairs.js provides a 1-to-1 mapping to the Rasha.js and Eckles.js APIs for the following:

• generate(options)
• import({ pem: ‘---BEGIN…’ })
• export({ jwk: { kty: ‘EC’, … })
• thumbprint({ jwk: jwk })

If you want to know the algorithm-specific options that are available for those you’ll want to take a look at the corresponding documentation:

• See ECDSA documentation at Eckles.js
• See RSA documentation at Rasha.js