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Gossipsub and Encrypted Communication

SUBFROST uses the gossipsub protocol for efficient and scalable real-time messaging between peers. gossipsub is a pub/sub (publish/subscribe) protocol where peers can subscribe to topics and receive messages that are published to those topics.

This is a core component of the subp2p networking layer and is used for a variety of tasks, such as broadcasting transaction and block information, and coordinating multi-party computations like FROST signing ceremonies.

Topics​

gossipsub topics are simple strings that are used to identify a particular message channel. Peers can subscribe to any topic, and they will receive all messages that are published to that topic by their connected peers.

In SUBFROST, topics are used to create logical communication channels for different purposes. For example, there might be a topic for all messages related to a specific frBTC contract, or a topic for a particular FROST signing group.

Encrypted Communication Channels​

While all communication on the subp2p network is encrypted at the transport layer (using TLS), gossipsub itself does not provide end-to-end encryption for messages. This means that any peer that is subscribed to a topic can read all the messages that are published to that topic.

However, it is possible to build a layer of end-to-end encryption on top of gossipsub to create private, encrypted communication channels. This is a powerful pattern that can be used to build secure group chat, private data sharing, and other applications that require confidentiality.

A Pattern for Secure Group Communication​

A common pattern for creating an encrypted communication channel on top of gossipsub is as follows:

  1. Establish a Shared Secret: A group of peers who want to communicate privately must first agree on a shared secret key. This could be done using a key exchange protocol like Diffie-Hellman, or by deriving the key from a common secret, such as a FROST group public key.

  2. Derive a Topic and Encryption Key: The shared secret can then be used to derive both a unique gossipsub topic and a symmetric encryption key. For example, the hash of the shared secret could be used as the topic, and the secret itself could be used as the encryption key.

  3. Encrypt and Publish: When a peer wants to send a message to the group, it first encrypts the message using the shared encryption key, and then publishes the encrypted message to the derived gossipsub topic.

  4. Receive and Decrypt: Only the peers who are part of the group and have access to the shared secret will be able to derive the topic, subscribe to it, and decrypt the messages.

This pattern effectively creates a private, end-to-end encrypted communication channel over the public gossipsub network. It is a powerful example of how the modular components of SUBFROST can be combined to build complex and secure decentralized applications.

gossipsub in SUBFROST​

The subfrost-cli uses gossipsub to broadcast messages to the network and to participate in FROST signing ceremonies. When you run the subfrost-cli, it subscribes to a set of default topics that are used for general network communication. It also subscribes to topics that are specific to the FROST signing groups that it is a part of.

Publishing and Subscribing to a Topic​

Here is an example of how to use gossipsub to publish and subscribe to a topic:

use subp2p::Subp2p;
use subp2p::gossipsub::{GossipsubEvent, IdentTopic as Topic};

// Create a new subp2p node
let mut subp2p = Subp2p::new().await?;

// Subscribe to a topic
let topic = Topic::new("my-topic");
subp2p.subscribe(&topic)?;

// Publish a message to the topic
subp2p.publish(topic.clone(), "my-message".as_bytes())?;

// Wait for a message to be received
loop {
    if let Subp2pEvent::Gossipsub(GossipsubEvent::Message { propagation_source, message_id, message }) = subp2p.next_event().await {
        println!("Received message: {:?}", message.data);
        break;
    }
}