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Encrypted Chat Example ​

Github Link (npm i && npm run dev to run, hosted demo coming soon)

The encrypted chat example implements simple private messaging for up to 2 people, and can be easily extended to groups of up to ~100 people.

ts
const models = {
  encryptionKeys: {
    address: "primary",
    key: "string",
  },
  encryptionGroups: {
    id: "primary",
    groupKeys: "string",
    key: "string",
  },
  privateMessages: {
    id: "primary",
    ciphertext: "string",
    group: "string",
    timestamp: "integer",
    $indexes: [["timestamp"]], // ["group", "timestamp"]
  },
}

const actions = {
  registerEncryptionKey: (db, { key }, { address }) => {
    db.set("encryptionKeys", { address, key })
  },
  createEncryptionGroup: (db, { members, groupKeys, groupPublicKey }, { address }) => {
    if (members.indexOf(fromCAIP(address)) === -1) throw new Error()
    const id = members.join()

    db.set("encryptionGroups", {
      id,
      groupKeys: JSON.stringify(groupKeys),
      key: groupPublicKey,
    })
  },
  sendPrivateMessage: (db, { group, ciphertext }, { timestamp, id }) => {
    db.set("privateMessages", { id, ciphertext, group, timestamp })
  },
}

Registering Encryption Keys ​

Users derive an individual encryption key when they log into the application, by signing a fixed message. [1]

The derived entropy is used to create an Ethereum private key/address pair, and this address is published in the encryptionKeys table.

Other users can see which users have registered to receive private messages by inspecting the table. Anyone holding the Ethereum wallet can re-derive the encryption key by signing the same message.

Creating Encryption Groups ​

Anyone can start a private message by creating a 2-person encryption group.

  • To create an encryption group, we generate another random private key, the group encryption key, which will be published in the key field of encryptionGroups.
  • We encrypt the group encryption key, using each of the group members' individual encryption keys, and store it in groupKeys.
  • Finally, we identify each encryption group by id, the lexicographically sorted, concatenated list of addresses in the group.

Sending Messages ​

To send a message to a group, we encrypt it using the group key, and publish it in the privateMessages table.

Further Work ​

This is a demo; later versions of this protocol might add some of these features:

  • Ability for a user to derive multiple encryptionKeys. Right now, we assume that wallets correctly implement RFC-6979, and so the db.encryptionKeys mapping will never be overwritten, but this assumption might be violated in edge cases.
  • Requiring individuals to acknowledge that a group was correctly created, and/or using a zero-knowledge proof in the createEncryptionGroup process to show that the group key was encrypted correctly to each individual within the group.
  • Ratchets to enforce key rotation for groups.
  • Privacy-preserving broadcast using protocols like Waku.

Deploying to Railway ​

Create a Railway space based on the root of this Github workspace (e.g. canvasxyz/canvas).

  • Custom start command: ./install-prod.sh && npm run start:server --workspace=@canvas-js/example-chat-encrypted
  • Custom build command: npm run build && npm run build --workspace=@canvas-js/example-chat-encrypted
  • Public networking:
    • Add a service domain for port 8080.
    • Add a service domain for port 4444.
  • Watch path: /examples/encrypted-chat/**. (Only build when chat code is updated, or a chat package is updated.)

  1. Ethereum wallets implement RFC-6979 so signatures are deterministic. To be extra careful, for financial or mission-critical applications, you may want to prompt for a signature twice the first time seeing a user. ↩ī¸Ž