In 2021, the Tor Project completed the migration from V2 to V3 onion addresses, deprecating a twelve-year-old standard in favour of a cryptographically stronger architecture. For users of .onion services, the change had immediate and lasting implications for both security and address format.
What Changed: V2 vs V3
V2 onion addresses were 16 characters long and derived from the first ten bytes of the SHA-1 hash of a 1024-bit RSA public key. By 2020, SHA-1 was considered cryptographically weak, and 1024-bit RSA keys were approaching the boundary of practical factorisation by well-resourced adversaries. V3 addresses are 56 characters long and use Ed25519 elliptic curve cryptography, which provides significantly stronger security per bit compared to RSA. The address is derived from the full public key, not a truncated hash, eliminating one layer of abstraction and strengthening the binding between an address and its service.
The Security Implications
The switch to V3 addresses closed several attack vectors that had been theoretical concerns under V2. Enumeration attacks, in which an adversary could systematically probe the network to discover hidden services, became significantly harder. The stronger cryptographic binding made it more difficult for attackers to create convincing spoofed addresses. End-to-end authentication between the client and the hidden service was also improved, reducing the risk of certain man-in-the-middle scenarios.
Impact on Darknet Marketplaces
The migration required all hidden service operators, including darknet marketplaces, to generate new V3 addresses and communicate them to their users. For markets with established user bases, this created a transition challenge: users needed to update bookmarks and verify new addresses, and phishing sites immediately began mimicking the new address format. Markets that handled the transition well published their new V3 addresses through multiple verified channels simultaneously and encouraged users to verify addresses against their PGP-signed announcements.
V3 Addresses Today
V3 onion addresses are now the exclusive standard on the Tor network. Any service still operating on a V2 address is inaccessible to current Tor Browser versions. The TorZon onion address and all verified mirror links use the V3 format, which can be identified by its 56-character length and the absence of the older, shorter format.
The upgrade to V3 represented one of the most significant improvements to hidden service security in Tor's history. Understanding how and why it matters helps users make more informed decisions about which services they trust.