Bitcoin still relies  on the internet as rails to reach consensus and is thus susceptible to  many traditional chokepoints. Reachable peers  that are able to both send and receive connections from the Bitcoin  blockchain number only slightly over 10,000. These nodes are capable of  fully validating the Bitcoin Blockchain and are a vital check on miners.Mining Centralization
While miners' interests are mostly aligned with users, their move towards industrial scale in areas of cheap electricity makes anonymity difficult with most relying on electricity off government grids. The inherent risk of censored transactions is only ensured against by having a robust and decentralized network of full nodes.

Unreachable Peers
It is a misconception that full nodes are the only non-mining nodes. The  vast majority of nodes are unreachable nodes, including mobile nodes,  those behind firewalls like Tor or even those shielded by Network  Address Translation. While these nodes are less discussed, they  represent the majority of the network.

A 2018 study, Towards Better Understanding of Bitcoin Unreachable Peers, finds Bitcoin unreachable nodes are highly centralized. If users elect to  forego a full node, they are sacrificing security not just for  themselves, but also for the entire network.

The data demonstrate the overwhelming majority of Bitcoin is used through mobile wallets with  the majority running on software from only two wallet providers,  BitcoinWallet & BreadWallet, providing for 59.9% and 20% of clients  respectively. This problem likely is, in part, a result of the prevalence of cryptocurrency purchases over mobile, making a mobile  wallet the most obvious destination following a purchase.

To  novice users, there are no apparent direct economic benefits to running a  full node. Instead, they elect to use wallets that ping between three  and six other random nodes to get up to date with the network. Full  nodes meanwhile keep a full history of the network dating back to the  genesis block.

In controlling nearly 80% of the share of  unreachable nodes on the network collectively, these two wallet  providers are in charge of a daunting amount of transaction propagation  to the point they can be considered critical to Bitcoin's  infrastructure. Institutions within Bitcoin should under no  circumstances be entrusted to provide the infrastructure for eighty  percent of non-listening nodes. When weighing the share of Bitcoiners  using mobile, the benefits of decreasing block size in order to implement mobile full nodes becomes even more paramount.Mobile Routing

Mobile  wallets connect through telecom companies, meaning the routing falls on  a limited number of service providers - namely T-Mobile, Verizon,  Comcast, ATT, and Rogers. These traditional communication rails are  designed to ease onboarding at the cost of security and user autonomy.  They make up  0.07% of the observable Autonomous Systems, and the five major telecom  hosts make up 16% of the networks unreachable peers, demonstrating a  clear lack of fault tolerance to routing attacks as well as in the  software managing transactions. Additionally, at the time  of this research, the top 100 Autonomous System routed 61% of  transactions for peers across the network. Throughout history, internet  service providers have shown a tendency to consolidate, with further  consolidation representing greater Bitcoin centralization.

IP centralization exposes Bitcoin to all sorts of malicious attacks. IPs  can wreak havoc on the network by delaying the propagation of blocks, or  by hijacking all IPs prefixes, then subsequently dropping all  interconnected routes to partition the network in half. Two Bitcoins  unable to communicate with one another create parallel blockchains and  could create havoc on commerce; unaware transactions are only being  published to a partitioned network.

Going Forward
It  is unlikely that there will suddenly be a shakeup in the  telecommunications industry, and if Bitcoin users continue to rely  heavily on traditional lines for internet money, they will be exposed to  traditional bottlenecks associated with them.

While we may  see some elect to provide internet service for themselves, it is  unreasonable for the majority of the non-technically community, and thus routing will continue to be an issue going down the road. While  software-defined radio represents an interesting way to communicate  among nodes without relying on traditional communication rails, users  are few and far between, and in the foreseeable future, it is not a  reputable option for most users. However, the Bitcoin holders' strong  community and deep pockets are an advantage that earlier bootstrapping  of amateur radio did not have.

While many may argue that the  satellite infrastructure provided by Blockstream can give users an  alternative route to connect to the network and a constant peer to help avoid partitions, the reality is users are pointing their dish into the  sky toward only one relaying peer who is controlled by a regional  telecommunications company. While satellites do avoid IPs, only one  off-grid accessible peer exposes users to similar risks.

100 IPs are associated with 89% of all the propagations, and 50 unreachable IPs are involved in 43% of all the propagations.

Network  centralization can easily create a "bottleneck" threat where the likes  of BreadWallet & BitcoinWallet or a major telecommunication company  create chokepoints in the network. The Bitcoin ecosystem would benefit  tremendously from more competition in the mobile wallet space. Going  forward, it appears it is becoming more important to find alternative  ways to broadcast and receive Bitcoin transactions as a dependance on  centralized telecommunications companies creates inherent risk for  Bitcoin. Protocols like SABRE have been put forth to protect Bitcoin  block promulgation by providing a stable infrastructure capable of  dealing with complex denial of service attacks. It will take a  comprehensive combination of new protocols and routing mechanisms in  order to protect Bitcoin from its own users if they continue to pile in  behind the same gates.

by Francis