Redazione RHC : 27 November 2025 06:54
The Tor project has announced the introduction of a new encryption scheme, called Counter Galois Onion (CGO) , intended to replace the previous Tor1 Relay method. The update aims to strengthen network security and counter threats from online attackers. The new system has already been implemented in Arti , the Rust implementation of Tor, and in the C version of Tor Relay.
According to the development team, the old Tor1 system had three main weaknesses: vulnerability to tagging attacks , lack of forward secrecy , and insufficient authentication strength . Among these, tagging attacks are considered the most significant risk, as Tor1 uses AES-CTR without support for hop-by-hop authentication. This leaves room for potential attempts to deanonymize users.
Furthermore, Tor1 did not guarantee immediate secrecy: the same AES key remained active for the entire lifespan of the circuit (the path a user took to connect to a website). Therefore, a compromised key could decrypt all historical traffic on that circuit.
Tor1’s authentication system was also limited: it used a mere 4-byte digest based on SHA-1, increasing the likelihood of manipulated data packets going undetected to one in four billion. CGO replaces this digest with a 16-byte token, significantly improving security.
To ensure real-time secrecy, CGO employs a structure called Update , which irreversibly changes the encryption key every time a packet is generated or received.
This prevents the decryption of previous packets. Furthermore, thanks to the use of extended block ciphers, any tampered data becomes unrecoverable, drastically reducing the risk of tagging attacks.
Tor Browser and Tails OS users will automatically benefit from the update without any manual intervention. The Tor network remains one of the primary tools for anonymous online browsing, with Tor Browser, Tails OS, and Orbot serving as the primary access points to the technology.
The CGO update is currently available for Arti and Tor Relay in C, but the Tor team has not yet provided a release date for the new encryption for the Tor browser.
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