A cryptographic tool for the deterministic generation of unique user IDs, and NaCl cryptographic keys
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sessionKeys (JavaScript)


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sessionKeys is a cryptographic tool for the generation of unique user IDs, and NaCl compatible Curve25519 encryption, and Ed25519 digital signature keys using JavaScript.

It is compatible with grempe/session-keys-rb which can generates identical IDs and crypto keys server-side using Ruby when given the same username and passphrase values. Both libraries have extensive tests to ensure they remain interoperable.


The encryption and signing keys are created with TweetNaCl.js, a port of TweetNaCl / NaCl to JavaScript for modern browsers and Node.js. The encryption keys are for the Public-key authenticated encryption box construction which implements curve25519-xsalsa20-poly1305. The signing keys are for the Ed25519 digital signature system.

The strength of the system lies in the fact that the keypairs are derived from passing an identifier such as a username or email address, and a high-entropy passphrase through the SHA256 cryptographic one-way hash function, and then 'stretching' that username/password into strong key material using the scrypt key derivation function.

The benefit of this approach are manifold:

  • Cryptographically secure key generation, full 32 byte (256 bit) keys
  • Risk of brute force attempts at key discovery likely eliminated
  • A deterministic ID protects user privacy when used in place of stored username on server
  • No need to manage or move keypairs around for use on different devices
  • Users never need to store sensitive key material on disk
  • Key material can't be stolen or copied without compromise of username/passphrase
  • Key material is deterministic, same username/passphrase always results in same keys
  • Multiple sets of key material are generated, allowing applications to secure different things with different keys
  • Cross language, Javascript and Ruby currently supported.

The code is simple and easily auditable, and uses only the fast and secure SHA256 hash function, scrypt for strong key derivation, and the NaCL compatible encryption and digital signature keys provided by tweetnacl-js.

This code was inspired by, but is incompatible with, the session25519 library created by Johannes Jörg Schmidt (@jo).

It bears repeating that the strength of this system is very strongly tied to the strength of the passphrase chosen by the user. Application developers are strongly encouraged to enforce the use of high-entropy passphrases by their users. Memorable high-entropy passphrases, such as can be generated using Diceware, and measured with password strength estimation tools like zxcvbn, are critically important to the overall security of this system.


Simply pass in a user identifier, such as an email address and a high-entropy passphrase. The callback will return an Object Literal with the key material.

A total of 256 bytes of key material is derived, and this is split into 8 32 byte keys which are returned as an Array of Uint8Array objects with raw binary data.

Each of those keys are also returned as hex values, and derived encryption and signing keypairs with Base64 encoded versions as well for convenience. This gives you eight different secure keys to choose from with various representations.

var sessionKeys = require('session-keys')

sessionKeys.generate('user@example.com', 'my secret password', function(err, keys) {
  // {
  //   id: "0123456789abcdef",
  //   byteKeys: [...],
  //   hexKeys: [...],
  //   naclEncryptionKeyPairs: [...],
  //   naclEncryptionKeyPairsBase64: [...],
  //   naclSigningKeyPairs: [...],
  //   naclSigningKeyPairsBase64: [...],
  // }

Cryptographic Design

The following pseudo-code illustrates how sessionKeys derives keys from a user ID and passphrase.


// 32 Byte hash of the user name
id = SHA256(username)

// 32 Byte hash of the password
key = SHA256(password)

// 32 Byte hash of the ID, its length, and a library specific string
salt = SHA256(id + idLength + 'session_keys')

// scrypt params
// 256 bytes of scrypt output
derivedBytes = scrypt(key, salt, N = 16384, r = 8, p = 1, dkLen = 256)

// Return all of the following

// The hex encoded sha256(username)
idhex = hex(id)

// Split the 256 derived bytes into 8 * 32 byte Uint8Array keys
byteKeys = []

// For each byteKey generate:

  // An Array of the hex values of each byteKey
  hexKeys = []

  // An Array of NaCl Encryption keys seeded from each byteKey
  naclEncryptionKeyPairs = []

  // An Array of NaCl Encryption keys seeded from each byteKey, Base 64 encoded
  naclEncryptionKeyPairsBase64 = []

  // An Array of NaCl Signing keys seeded from each byteKey
  naclSigningKeyPairs = []

  // An Array of NaCl Signing keys seeded from each byteKey, Base 64 encoded
  naclSigningKeyPairsBase64 = []


The author of scrypt-async-js, which is the strong key derivation mechanism used by sessionKeys, recommends using setImmediate:

Using setImmediate massively improves performance. Since most browsers don't support it, you'll have to include a shim for it.

Performance in this context is not about making the key derivation run faster, as that would kind of defeat the purpose. It is instead about ensuring your application remains responsive while this code is running.








This project now manages all dependencies with yarn which you'll need to install first.

Make sure you are using v0.16.0 or higher.

$ yarn -V

Install all dependencies locally.



You can build a dist version of sessionKeys using browserify. There is a pre-built version in the dist directory of this repository which includes all dependencies and can be used with a <script> tag in the browser.

yarn run build


# run all tests locally with node
yarn test

# run all tests locally from test.html in your default browser
# test output will be in your browser's console.
yarn run test-browser

Installation Security : Signed Git Commits

Most, if not all, of the commits and tags in the repository for this code are signed with my PGP/GPG code signing key. I have uploaded my code signing public keys to GitHub and you can now verify those signatures with the GitHub UI. See this list of commits and look for the Verified tag next to each commit. You can click on that tag for additional information.

You can also clone the repository and verify the signatures locally using your own GnuPG installation. You can find my certificates and read about how to conduct this verification at https://www.rempe.us/keys/.


Bug reports and pull requests are welcome on GitHub at https://github.com/grempe/session-keys-js. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.



(c) 2016 Glenn Rempe <glenn@rempe.us> (https://www.rempe.us/)


The gem is available as open source under the terms of the MIT License.


Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the LICENSE.txt file for the specific language governing permissions and limitations under the License.

Thank You!

Thanks to Dmitry Chestnykh (@dchest) and Tony Arcieri (@bascule) for all the great code and help, and Johannes Jörg Schmidt (@jo) for the original implementation.