Bitcoin Core Weighs Dropping CJDNS Support Over Eclipse Attack Risk
Bitcoin Core developers are debating whether to drop support for CJDNS, an encrypted alternative routing network the software has offered for years as an optional transport layer, after a network scan found the entire CJDNS peer pool had shrunk to just seven reliably reachable nodes.
CJDNS was originally added to Bitcoin Core as one option among several, alongside IPv4, IPv6, Tor, and I2P, giving node operators an encrypted fallback route if one of the other networks ran into trouble. That design assumed a reasonably healthy, independent peer pool behind each option. The recent scan undercut that assumption for CJDNS specifically: of 25 known CJDNS addresses in one seeder’s database, only seven were classified as good.
Seven reliable peers is a small enough pool that it stops functioning as a security fallback and starts becoming a liability. A node relying exclusively on CJDNS for connectivity has so few possible peers that an attacker needs comparatively few resources to monopolize its entire inbound and outbound connection set, the exact eclipse-attack scenario that a diverse routing layer is supposed to prevent in the first place.
The proposal on the table takes a staged approach rather than an immediate cut: Bitcoin Core 32.x would ship a warning about CJDNS’s degraded state, with actual removal reserved for version 33.x if the network doesn’t recover in the meantime. Developers pushing for removal have also pointed to the ongoing maintenance burden CJDNS code places on the wider Core repository, arguing that carrying a networking option nobody can rely on isn’t worth the upkeep cost.
The debate is a reminder that a security feature’s value depends entirely on real-world adoption, not just its design on paper. An encrypted routing option that looks good in documentation but has fewer reliable peers than a small Discord server isn’t adding resilience, it’s quietly subtracting it.
Curious how Bitcoin’s peer-to-peer network defends against eclipse attacks? Explore more in our Bitcoin Academy.