Evaluation of the Arweave yellow paper (#11)

* Evaluation of Arweave

* Update arweave with comments from team

evaluations/arweave.md

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+An evaluation of the Arweave paper
+==================================
+
+2021-05-18 Dagger Team
+
+https://www.arweave.org/yellow-paper.pdf
+
+Goal of this evaluation is to find things to adopt or avoid while designing
+Dagger. It is not meant to be a criticism of Arweave.
+
+#### Pros:
+
++ There is no distinction between full and light clients, merely clients that
+  downloaded more or less of the blockweave. (§2.2)
++ Prefential treatment of peers is discouraged, because nodes are unaware when
+  they're being monitored for responsiveness. (§3.4.2)
++ Interesting 'meta-game' on top of tit-for-tat, in which nodes monitor their
+  peers on how they rank other peers. (§6.1)
++ Because behaviour of nodes is largely based on local rules and the local view
+  that a node has of its peers, the network is able to shift behaviour gradually
+  in response to a changing environment. (§6.2)
+
+#### Cons:
+
+- Proof of Work is used for the underlying blockweave (§3.1), which is
+  rather wasteful.
+- Data is stored indefinitely, which is great for public information, but not so
+  great for ephemeral private data. This makes storage unnecessarily expensive
+  for data with a short lifespan. (§3.1)
+- Network is free at point of use for external users, raising questions about
+  scalability of the network when faced with highly popular content. (§3.4.2)
+  Incentives for data replication help (§7.1.2), but it is unlikely that it
+  will hold up when the network grows in content (§8.2, §8.3). These incentives
+  can also lead to unnecessary duplication of unpopular content.
+- Nodes with limited connectivity are discouraged from participating in the
+  network, which precludes use on mobile devices. (§3.4.3)
+- There is an economic incentive for a miner to not to share old blocks with
+  other miners, because it increases its chance of "winning" the new block.
+  (§4.1.1)
+- There is an economic incentive for miners to have the strictest censorship
+  rules, because otherwise a block that it mined might be rejected by others.
+  (§5.1)
+- The majority of the network determines the censorship rules. This could prove
+  troublesome should Arweave's Proof of Work lead to similar geographic
+  centralization of mining power as we see in Bitcoin. (§5.3)
+- Transaction ID is used for addressing, instead of a content hash. (§7.1.1)
+- Uses HTTP for inter-node traffic, instead of an established peer-to-peer
+  protocol. (§7.1.3)