dagger-research/evaluations/swarm.md

An evaluation of the Swarm book

2020-12-22 Mark Spanbroek

https://swarm-gateways.net/bzz:/latest.bookofswarm.eth/

Goal of this evaluation is to find things to adopt or avoid while designing Dagger. It is not meant to be a criticism of Swarm.

Pros:

• Book contains a well-articulated vision and historical context (§1)
• Uses libp2p as underlay network (§2.1.1)
• Uses content-addressable fixed-size chunks (§2.2.1, §2.2.2)
• Employs encryption by default, enabling plausible deniability for node owners (§2.2.4)
• Opportunistic caching allows for automatic scaling for popular content (§2.3.1, §3.1.2)
• Has an upload protocol that, once completed, allows the uploader to disappear (§2.3.2)
• Network self-repairs content through pull syncing (§2.3.3).
• Nodes can play different roles depending on their capabilities, e.g. light node, forwarding node, caching node (§2.3.4).
• Has a pricing protocol (§3.1.2)
• Uses micro payments (§3.2)
• Allows for zero cash entry (§3.2.5), which benefits decentralization
• Uses staking/collateral, spot-checks and litigation to insure long term storage. (§3.3.4, §5.3)
• The Merkle tree for chunking a file enables random access, and resumption of uploads (§4.1.1)
• Manifests allow for collections of files and their paths (§4.1.2)
• Combines erasure coding with a Merkle tree in a smart way (§5.1.3)
• Redundancy is used to improve latency (§5.1.3)

Cons:

• Use of two peer-to-peer networks (underlay and overlay) seems overly complex (§2.1)
• Tries to solve many problems that can be addressed by other protocols, such as routing privacy, micro payments and messaging.
• Storage nodes and peers are chosen based on their mathematical proximity, instead of taking performance and risk into account (§2.1.3)
• Uses a forwarding Kademlia DHT (§2.1.3) for routing, which requires stable, long lived network connections
• Depends heavily on forwarding of messages, each message passes through list of peers that could be on opposite sides of the world. (§2.1.3)
• Tries to solve routing privacy (§2.1.3), which could arguably be better addressed by a separate protocol such as onion routing.
• Because of the use of an overlay DHT network, Swarm has to solve the bootstrapping problem, even though libp2p already solves this (§2.1.4).
• A Swarm node needs to maintain three different DHTs; one for the underlay network (libp2p), another for routing (forwarding Kademlia), and a third for storage (DISC).
• Solves the problem of changing content in a content-addressable system in two different ways: through single-owner chunks (§2.2.3), and through ENS (§4.1.3)
• Garbage collection based on chunk value makes it hard to reason about the amount of money that is required to keep content on the network (§2.2.5)
• Besides all the various incentives, Swarm also has a reputation system in the form of a deny list (§2.2.7).
• Incentive system is complex, and therefore harder to verify. (§3)
• Has its own implementation of micro payments, instead of using existing payment channels (§3.2.1)
• Rewarding nodes for upload receipts leads to a store-and-forget attack, that requires tricky mitigation (§3.3.4)
• Extra complexity (trojan chunks, feeds) is added because Swarm is also a fully fledged communication system (§4).
• Offers pinning of content, even though it is inferior to using incentives (§5.2.2)
• Recovery is built on top of pinning and messaging (trojan chunks) (§5.2.3)