privacyresearchgroup / signal-demo-backend

Simple Signal Server

This repository implements the server components needed to run a simple signal service: a directory/key service and a message service. It is built only to support demonstrations of Signal Protocol SDKs and is not a recommended production system.

Getting Started

Run yarn to install all of the needed dependencies, then deploy using the following command:

sls deploy --stage mystagename --aws-profile myawsprofile

This creates a Websocket and a REST API that are now ready to use. Information about the newly created stack will appear in the console.

Enpoints and Resources

The deployment creates the following REST API endpoints:

• keys/{address} PUT - Registers the keys for a user with the address in the path. Expects a request body of type FullKeyBundle as defined in key-table.ts.
• keys/{address} GET - Gets a PublicPreKeyBundle as defined in key-table.ts containing exactly one of the one-time keys for the user at the given address. Removes that one-time key from the database.
• messages/{address} POST - Sends a message to an address. In practice these will be base 64 encoded protobuf messages, but can be arbitrary strings.
• messages/{address} GET with query string ?after=<timestamp> - retrieves all messages for a user after the given timestamp.

Accessing Services from the Command Line

In what follows we will walk through the use of each of the published endpoints and websocket actions using curl and wscat. This allows us to test deployments and makes it clear how to access the resources in code.

Use the REST API to Upload Keys

To upload a keyset to the service at address markj with the following content

{
  "registrationId": 1,
  "identityKey": "ABC123",
  "signedPreKey": {
    "keyId": 2,
    "publicKey": "aPublicKey",
    "signature": "thisigisinvalid"
  },
  "oneTimePreKeys": ["DEF456", "GHI789"]
}

store it in a document called fullkeybundle.json and run the following command:

curl -X PUT -H "Content-Type: application/json" -H "x-api-key: <yourapikey>" -d @./fullkeybundle.json https://<apiID>.execute-api.us-west-2.amazonaws.com/<mystagename>/keys/markj

Note the address markj in the URL. You will need to substitute your own apiID and yourapikey.

Use the REST API to Fetch a PreKey Bundle

To get a PreKey bundle for user markj, run the following command:

curl -H "x-api-key: <yourapikey>" https://<apiID>.execute-api.us-west-2.amazonaws.com/<mystagename>/keys/markj

Run it multiple times and note that the preKey is different each time until the preKeys are all used up, then there is no preKey.

Use the REST API to send and recieve messages

To send a message to address markj:

curl -X POST -H "x-api-key: <yourapikey>" -H "Content-Type: application/json" -d "hi markj" https://<apiID>.execute-api.us-west-2.amazonaws.com/<mystagename>/messages/markj

and to get all messages to markj after timestamp 1596600000000:

curl -H "x-api-key: <yourapikey>" https://<apiID>.execute-api.us-west-2.amazonaws.com/<mystagename>/messages/markj?after=1596600000000

Use the Websocket to send a message

First connect to the websocket using wscat (which can be installed globally with npm install -g wscat if not already):

wscat -c wss://<websocketID>.execute-api.us-west-2.amazonaws.com/<mystagename>

Then at the prompt subscribe to messages for markj and pantani:

> {"action": "subscribe", "channels": ["markj", "pantani"]}

Send a message to pantani:

> {"action": "sendMessage", "address": "pantani", "message": "somebase64Enc0d3dprotobuf4u"}

And if you subscribed to pantani you'll see this:

< somebase64Enc0d3dprotobuf4u

Finally let's get all recent messages for markj

> {"action": "recent", "address": "markj"}

License

This project is licensed under GPL v3.

Copyright 2020 - Privacy Research, LLC