What is OnionCat?

OnionCat is a peer-to-peer layer 3 VPN which is based on Tor or I2P. Thus, it offers typical VPN functionality with the addition of location-based anonymity.

With OnionCat you can connect two or more computers virtually together (as if they were connected to a switch) through the Tor network thereby staying anonymous.

Do I need IPv6 Internet to run OnionCat?

No. Your system has to have IPv6 enabled which is enabled on most modern operating systems by default but you do not need an IPv6 Internet uplink.

Is OnionCat really anonymous?

OnionCat solely relies on Tor for anonymity.

What license does OnionCat have?

OnionCat is released under GPLv3. Additionally, It contains the original unmodified source of the two functions strlcat() and strlcpy() from OpenBSD with its original license.

Will ocat and gcat help me circumvent surveillance like PRISM?

Yes, it definitely will to some extent!

Since ocat relies on Tor hidden services and gcat uses I2P for transport, your communication will be safe from being eavesdropped or manipulated. Also, the mechanisms behind those transports maintain your anonymity ( observers can’t tell where information comes from and – consequently – where it goes ).

Additionally, you always know that you’re talking to the correct endpoint so that no one will be able to misleadingly pretend to be your desired communication partner ( IP address ).

… to some extent?

Yes – data you’re providing about yourself ( e.g. posting to blogs, forums, etc. ) will of course leak your personal data, even if they reside within the ocat / gcat universe. You should always try to avoid providing too much personal information.


… and what about telephony?

While the described features only cover the Internet-related parts of PRISM, ocat and gcat can also protect your privacy and anonymity using voice communication. Both felines provide transparent IPv6 layers for your convenience, allowing every application that is IPv6 aware to tunnel its packets to an ocat or gcat enabled endpoint. SIP telephony is an open standard, capable of using IPv6 ( if implemented into your SIP software ) and therefore recommended to make cheap and secure voice calls. Using teamspeak and ventrilo are also possible ways to keep the NSA from poking their nose into your conversation.

To bring such features to your smartphones, onioncat must be ported to your favourite mobile platform. Additionally, you will need the respective transport available on your devices operating system. Android users can already take advantage of Orbot, the official Tor port for Googles mobile platform.

You can see that ocat and gcat, along with Tor and I2P, will circumvent PRISM ( and other surveillance programs driven by central wiretapping ) and did so for several years now.

Don’t let governments and affiliated groups mess around with your data – regain your privacy and encrypt your communication wherever you can!

Can I route IPv4 through OnionCat?

Yes, if you setup a tunnel. OnionCat itself forwards only IPv6 but IPv6 natively supports encapsulation of IPv4. You need to configure an IP-in-IPv6 tunnel. A short How-To is found in the old OnionCat Trac at www.cypherpunk.at/onioncat_trac/wiki/IPv4.

Can I access the Internet through OnionCat?


OnionCat does not magically tunnel IP traffic to the Internet. OnionCat does not tunnel traffic to the Internet at all, although it is possible to create such a setup but this is beyond the scope of this FAQ.

What are the use cases for OnionCat?

You can securely connect to e.g. your server(s) accessing all its network services without being surveilled.

You could also use it to circumvent firewalls if you want to connect to your server’s services (see Evading Firewalls).

What does OnionCat *NOT* do?

OnionCat does not magically forward your traffic to the Internet. You cannot access the Internet with it and OnionCat does not route all your IP traffic through Tor to the Internet.

OnionCat is not a method for accessing hidden services. OnionCat can only connect to other OnionCats.