Kademlia — A Peer-to-Peer Information System Based on the XOR Metric

Kademlia's defining choice is $d(x,y)=x\oplus y$. It induces prefix-based distance ranges and gives symmetric routes, so contacts learned while answering requests are useful to both parties. Nodes query $\alpha$ candidates concurrently, retain $k$ stable contacts per distance bucket, and replicate values near the key.

The original paper assumes a substantially friendlier identity environment than a modern permissionless network. Sybil and eclipse resistance must be added by the deployment; Ethereum discovery is explicitly Kademlia-like rather than a verbatim implementation.

Visual audit #

All 13 physical pages were rendered and inspected, using OCR because the embedded text encoding was corrupt. The binary-tree, bucket-partition, and lookup figures are load-bearing. GTK redraws the lookup loop independently and explains prefix geometry in prose; no source image is retained.