Zooko's triangle

Zooko's triangle is a trilemma of three properties that some people consider desirable for names of participants in a network protocol:
 * Human-meaningful: Meaningful and memorable (low-entropy) names are provided to the users.
 * Secure: The amount of damage a malicious entity can inflict on the system should be as low as possible.
 * Decentralized: Names correctly resolve to their respective entities without the use of a central authority or service.

Overview
Zooko Wilcox-O'Hearn conjectured that no single kind of name can achieve more than two. For example: DNSSec offers a human-meaningful, secure naming scheme, but is not decentralized as it relies on trusted root-servers; .onion addresses and bitcoin addresses are secure and decentralized but not human-meaningful; and I2P uses name translation services which are secure (as they run locally) and provide human-meaningful names - but fail to provide unique entities when used globally in a decentralised network without authorities.

Solutions
Several systems that exhibit all three properties of Zooko's triangle include: Several platforms implement refutations of Zooko's conjecture, including: Twister (which use Swartz' system with a bitcoin-like system), Blockstack (separate blockchain), Namecoin (separate blockchain), LBRY (separate blockchain - content discovery, ownership, and peer-to-peer file-sharing), Monero, OpenAlias, Ethereum Name Service, and the Handshake Protocol.
 * Computer scientist Nick Szabo's paper "Secure Property Titles with Owner Authority" illustrated that all three properties can be achieved up to the limits of Byzantine fault tolerance.
 * Activist Aaron Swartz described a naming system based on Bitcoin employing Bitcoin's distributed blockchain as a proof-of-work to establish consensus of domain name ownership. These systems remain vulnerable to Sybil attack, but are secure under Byzantine assumptions.
 * Theoretician Curtis Yarvin implemented a decentralized version of IP addresses in Urbit that hash to four-syllable, human-readable names.