Evaluation of Swarm (#4)

evaluations/swarm.md

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+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)