How Long Is a V3 Tor Onion Address?

A standard Version 3 (V3) Tor onion address is 56 characters long, excluding the .onion top-level domain. When including the .onion suffix, the total address length is 62 characters. This article explains the exact length, structural breakdown, and cryptographic design behind standard V3 onion addresses.

Exact Character Count

• Address Hash: 56 characters
• Top-Level Domain: 6 characters (.onion)
• Total Length: 62 characters

An example of a standard V3 onion address looks like this: vww6ybal4bd7szmgncyruucpgfkqahzddi37ktceo3ah7ngmcopnpyyd.onion

The Cryptographic Structure of 56 Characters

The 56-character string is encoded using Base32 (comprising the letters a-z and numbers 2-7). It represents a raw 35-byte binary payload structured into three specific parts:

1. Ed25519 Public Key (32 bytes): The full cryptographic public key for the hidden service, which eliminates the need for a central directory authority to verify ownership.
2. Checksum (2 bytes): A SHA3-256 hash output used by the Tor client to detect typos and verify data integrity before attempting a connection.
3. Version Field (1 byte): Identifies the onion address version (set to \x03 for V3).

When these 35 bytes are encoded into Base32, each character represents 5 bits of data, resulting in exactly 56 characters: (35 bytes × 8 bits/byte) ÷ 5 bits/character = 56 characters

V3 vs. Deprecated V2 Length

• V2 Onion Addresses (Deprecated): Were 16 characters long (plus .onion). They relied on an 80-bit truncated SHA-1 hash of an RSA-1024 public key, which became vulnerable to collision and brute-force attacks.
• V3 Onion Addresses (Current): Are 56 characters long. The increased length directly embeds the entire 256-bit Ed25519 public key, providing modern elliptic-curve cryptography and significantly stronger protection against network snooping and impersonation.