Add initial libp2p standardization

specs/networking/libp2p-standardization.md

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+ETH 2.0 Networking Spec - Libp2p standard protocols
+===
+
+# Abstract
+
+Ethereum 2.0 clients plan to use the libp2p protocol networking stack for
+mainnet release. This document aims to standardize the libp2p client protocols,
+configuration and messaging formats.
+
+# Libp2p Protocols
+
+## Transport
+
+This section details the libp2p transport layer that underlies the
+[protocols](#protocols) that are listed in this document.
+
+Libp2p allows composition of multiple transports. Eth2.0 clients should support
+TCP/IP and optionally websockets. Websockets are useful for implementations
+running in the browser and therefore native clients would ideally support these implementations 
+by supporting websockets.
+
+An ideal libp2p transport would therefore be TCP/IP with a fallback to
+websockets.
+
+### Encryption
+
+Libp2p currently offers [Secio](https://github.com/libp2p/specs/pull/106) which
+can upgrade a transport which will then encrypt all future communication. Secio
+generates a symmetric ephemeral key which peers use to encrypt their
+communication. It can support a range of ciphers and currently supports key
+derivation for elliptic curve-based public keys.
+
+Current defaults are:
+- Key agreement: `ECDH-P256` (also supports `ECDH-P384`)
+- Cipher: `AES-128` (also supports `AES-256`, `TwofishCTR`)
+- Digests: `SHA256` (also supports `SHA512`)
+
+
+## Protocols
+
+This section lists the necessary libp2p protocols required by Ethereum 2.0
+running a libp2p network stack.
+
+## Multistream-select
+
+#### Protocol id: `/multistream/1.0.0`
+
+Clients running libp2p should support the [multistream-select](https://github.com/multiformats/multistream-select/)
+protocol which allows clients to negotiate libp2p protocols establish streams
+per protocol.
+
+## Multiplexing
+
+Libp2p allows clients to compose multiple multiplexing methods. Clients should
+support [mplex](https://github.com/libp2p/specs/tree/master/mplex) and
+optionally [yamux](https://github.com/hashicorp/yamux/blob/master/spec.md)
+(these can be composed).
+
+**Mplex protocol id: `/mplex/6.7.0`**
+
+**Yamux protocol id: `/yamux/1.0.0`**
+
+## Gossipsub
+
+#### Protocol id: `/meshsub/1.0.0`
+
+*Note: Parameters listed here are subject to a large-scale network feasibility
+study*
+
+The [Gossipsub](https://github.com/libp2p/specs/tree/master/pubsub/gossipsub)
+protocol will be used for block and attestation propagation across the
+network.
+
+### Configuration Parameters
+
+Gossipsub has a number of internal configuration parameters which directly
+effect the network performance.  Clients can implement independently, however
+we aim to standardize these across clients to optimize the gossip network for
+propagation times and message duplication. Current network-related defaults are:
+
+```
+(
+	// The target number of peers in the overlay mesh network (D in the libp2p specs).
+	mesh_size: 6
+	// The minimum number of peers in the mesh network before adding more (D_lo in the libp2p specs).
+	mesh_lo: 4
+	// The maximum number of peers in the mesh network before removing some (D_high in the libp2p sepcs).
+	mesh_high: 12
+	// The number of peers to gossip to during a heartbeat (D_lazy in the libp2p sepcs).
+	gossip_lazy: 6 // defaults to `mesh_size`
+	// Time to live for fanout peers (seconds).
+	fanout_ttl: 60
+	// The number of heartbeats to gossip about.
+	gossip_history: 3
+	// Time between each heartbeat (seconds).
+	heartbeat_interval: 1
+)
+```
+
+### Topics
+
+*The Go and Js implementations use string topics - This is likely to be
+updated to topic hashes in later versions - https://github.com/libp2p/rust-libp2p/issues/473*
+
+For Eth2.0 clients, topics will be sent as `SHA2-256` hashes of the topic string.
+
+There are two main topics used to propagate attestations and beacon blocks to
+all nodes on the network.
+
+- The `beacon_block` topic - This topic is used solely for propagating new
+	beacon blocks to all nodes on the networks.
+- The `beacon_attestation` topic - This topic is used to propagate
+	aggregated attestations to subscribing nodes (typically block proposers) to
+	be included into future blocks. Attestations will be aggregated in their
+	respective subnets before publishing on this topic.
+
+Shards will be grouped into their own subnets (defined by a shard topic). The
+number of shard subnets will be defined via `SHARD_SUBNET_COUNT` and the shard
+`shard_number % SHARD_SUBNET_COUNT` will be assigned to the topic:
+`shard{shard_number % SHARD_SUBNET_COUNT}`.
+
+### Messages
+
+#### Libp2p Specification
+
+*This section simply outlines the data sent across the wire as specified by
+libp2p - this section is aimed at gossipsub implementers to standardize their implementation of this protocol*
+
+Libp2p raw gossipsub messages are sent across the wire as fixed-size length-prefixed byte arrays.
+
+The byte array is prefixed with an unsigned 64 bit length number encoded as an
+`unsigned varint` (https://github.com/multiformats/unsigned-varint). Gossipsub messages therefore take the form:
+```
++--------------------------+
+|     message length       |
++--------------------------+
+|                          |
+|       body (<1M)         |
+|                          |
++--------------------------+
+```
+
+The body represents a protobuf-encoded [Message](https://github.com/libp2p/go-libp2p-pubsub/blob/master/pb/rpc.proto#L17-L24). 
+
+In the following section we discuss the data being sent in the `data` field of
+the protobuf gossipsub `Message`.
+
+#### Eth2.0 Specifics
+
+Each message has a maximum size of 512KB (estimated from expected largest uncompressed
+block size).
+
+The `data` that is sent in a Gossipsub message is an SSZ-encoded object. For the `beacon_block` topic,
+this will be a `beacon_block`. For the `beacon_attestation` topic, this will be
+an `attestation`.
+
+## Eth-2 RPC
+
+#### Protocol Id: `/eth/serenity/beacon/rpc/1`
+
+The [RPC Interface](./rpc-interface.md) is specified in this repository.
+
+## Identify
+
+#### Protocol Id: `/ipfs/id/1.0.0` (to be updated to `/p2p/id/1.0.0`)
+
+*To be updated to incorporate discv5*
+
+
+The Identify protocol (defined in go - [identify-go](https://github.com/ipfs/go-ipfs/blob/master/core/commands/id.go) and rust [rust-identify](https://github.com/libp2p/rust-libp2p/blob/master/protocols/identify/src/lib.rs))
+allows a node A to query another node B which information B knows about A. This also includes the addresses B is listening on.
+
+This protocol allows nodes to discover addresses of other nodes to be added to
+peer discovery. It further allows nodes to determine the capabilities of all it's connected
+peers.
+
+### Configuration Parameters
+
+The protocol has two configurable parameters, which can be used to identify the
+type of connecting node. Suggested format:
+```
+	version: `/eth/serenity/1.0.0`
+	user_agent: <client name and version>
+```
+
+## Discovery
+
+#### Protocol Id: `/eth/serenity/disc/1.0.0`
+
+*To be updated to incorporate discv5*
+
+The discovery protocol to be determined.