Tor makes it possible for users to hide their locations while offering various kinds of services, such as web publishing or an instant messaging server. [...] other Tor users can connect to these onion services, formerly known as hidden services, each without knowing the other's network identity.
Tor Onion Services: Configuration
Newcomers to this topic are recommended to first read the following Tor Project and Riseup documentation entries to better understand how onion services work, how they are safely configured outside of Whonix ™, and suggested best practices:
- Tor: Onion Service Protocol [archive] (general information);
- Configuring Onion Services for Tor [archive] (standard setup, no isolated proxy); and
- Best Practices for Hosting Onion Services [archive] (installation, configuration and protecting services)
Onion addresses do not require Secure Sockets Layer (SSL) or Transport Layer Security (TLS) , because connections to Tor onion services are end-to-end encrypted by default.   This is handy, as it is unnecessary to bother with self signed certificates or certificate authorities.
Another interesting onion service property is they can serve as a drop-in Global Server Load Balancing and Layer 3 DDoS-resistance solution.  This raises the bar to withstanding attacks that the entire Tor network can tolerate; the same applies to I2P Eepsites. Tor can also be considered a very simple to configure, encrypted transport alternative to IPSec. 
Potential adversaries can detect whether the onion service (and presumably Tor) is up and running or not. Even if somebody hacks the hidden server software -- such as
apache -- the attacker cannot steal the onion service key or bypass Tor; see Attack on Whonix ™. The reason is the key is stored on the Whonix-Gateway ™. Once the Whonix-Workstation ™ is cleaned, it is no longer possible for an adversary to impersonate the onion service.
An exception to this is if onion services are created by software running on Whonix-Workstation ™ (examples documented at the time of writing are ZeroNet, OnionShare and Bisq).  This is opt-in and not happening by default or accident. When following the instructions on this page, this exception does not apply.
For possible alternatives to onion services, see: Hosting Location Hidden Services.
Web Server Software Recommendations
If your needs are limited to hosting static pages, then look no further than
micro-httpd which is available from Debian repositories. It is a bare-bones daemon made up of 150 lines of code. 
It is best to avoid the
Apache web server because it has much more functionality, leak potential and attack surface than smaller and lighter alternatives. If the Apache web server will be used regardless, refer to the following footnotes.  
Nginx web server is a recommended alternative to
Apache. If the
Nginx web server will be used regardless, refer to the following footnotes. 
Table: Onion Service Security Recommendations
|ALPaCA||An advanced website fingerprinting client/server mitigation named ALPaCA is in development that applies server-side padding to requests sent out to Tor Browser. When finalized, service operators can run it to protect against this class of correlation attacks.   |
|Application Level Leaks||Beware of application level leaks; see Protocol Leak Protection and Fingerprinting Protection for a definition.|
|Dedicated Onion Service Address||Each service you host should get its own dedicated onion address to prevent correlation between multiple instances running in the same VM.|
|Dedicated SSH Server Onion Address||If hosting onion services on remote servers: Each server you host remotely should get its own dedicated onion address different from its service onion address. For example if xxx.onion is your onion web service then yyy.onion should be your private SSH server onion address. This is to increase the probability of still being able remote administrate your server through SSH should your separate onion service address be under DDOS (flood overload, resource exhaustion attack). See also recommendations for Remote Administration.|
|Denial of Service (DoS) Attack Defense||A researcher has posted his experience keeping their onion up during a massive DDoS [archive]. |
|Disable Banners||Disable banners for SSH, FTP, SMTP and HTTP servers which leak information about the daemon's name and version. If the SSH instance is for private use, use it with an Authenticated Onion Service to protect the server from brute-force and remote exploitation.|
|General Hardening||Additional pointers for hardening can be found in the Basic Security Guide and Advanced Security Guide sections of the Documentation.|
|Hide IP Address||
|Mitigate DoS Attacks||It is good practice to setup access to your site through reverse proxies to mitigate layer 7 DoS attacks [archive]. See for example Mitigating DDoS Attacks with NGINX and NGINX Plus [archive]. That way it may also be possible to block information leaks about your setup.|
|OnionBalance||OnionBalance [archive] can help to prevent de-anonymization of an onion service by protecting it from becoming unavailable through denial of service attacks (DDOS). OnionBalance is mentioned in the security readme [archive] by vanguards author and Tor developer Mike Perry where he discusses attacks against onion services and defenses. OnionBalance [archive] is now available for onion v3 services , see: Cooking with Onions: Reclaiming the Onionbalance [archive].|
|Onion v3||No longer use onion v2; see here [archive].|
|Server Software Hardening||If any instructions for hardening the server instructions are available it is recommended to apply them, even though Whonix ™ is designed to prevent IP/DNS leaks.|
|Vanguards||Vanguards protect against guard discovery and related traffic analysis attacks and is installed by default in Whonix ™.  See Vanguards for further information.|
Perform all the following steps on the Whonix-Gateway ™.
Step 1: Open Tor Configuration
On the Whonix-Gateway ™.
Step 2: Edit Tor Configuration
Step 3: Configure Onion Services Authentication
Step 4: Denial of Service Mitigation Options
Documentation for Denial of Service Mitigation Options is incomplete. Contributions are happily considered!
Nothing Whonix ™ specific regarding installation from source. As per:
Step 5: Make Tor Configuration Changes Take Effect
On the Whonix-Gateway ™.
Step 6: Retrieve the Onion Hostname
On the Whonix-Gateway ™.
To retrieve your Tor onion service url, run.
sudo cat /var/lib/tor/hidden_service/hostname
Step 7: Backup the Tor Onion Service Private Key
On the Whonix-Gateway ™.
Reminder: Always backup the onion service key. This is necessary in order to restore it on another machine, on a newer Whonix-Gateway ™, after HDD/SSD failure, etc. Follow the instructions below to find its location; root permission is required to access it.
Perform all the following steps on the Whonix-Workstation ™.
Step 1: Install Server Software
On the Whonix-Workstation ™.
A) Run the following commands to install
B) Run the following commands to install
Step 2: Open Whonix-Workstation Firewall Port
On the Whonix-Workstation ™.
Modify Whonix-Workstation ™ User Firewall Settings
EXTERNAL_OPEN_PORTS+=" 80 "
Reload Whonix-Workstation ™ Firewall.
Step 3: Final Notes
The procedure is now complete.
Please note that it may take up to 30 minutes (or thereabouts) until a fresh .onion domain is reachable. Further, accessing
Local connections are no longer possible due to a change [archive] in Tor Browser by The Tor Project. Check Tor Browser, Local Connections for more information and a workaround.
sudo ls -la /var/lib/tor/hidden_service/
In case you manually restored the hidden_service keys as root, Tor will fail to start. The folder must be owned by
debian-tor. In that case, fix the permissions.
sudo chown debian-tor:debian-tor /var/lib/tor/hidden_service/
Check if the service is available on
## Circumventing Whonix ™ curl stream isolation wrapper. UWT_DEV_PASSTHROUGH=1 curl 127.0.0.1:80
## Circumventing Whonix ™ curl stream isolation wrapper. UWT_DEV_PASSTHROUGH=1 curl $(qubesdb-read /qubes-ip):80
Non-Qubes-Whonix ™: In Whonix-Workstation ™, check if the service is available on
## Circumventing Whonix ™ curl stream isolation wrapper. UWT_DEV_PASSTHROUGH=1 curl 10.152.152.11:80
Note: Tor Browser will allow connections to
127.0.0.1:80 but not to
Setup Tips for any Onion Service
Please test the example Hidden Webserver above first; this helps in understanding the process in general and will ease debugging. The following material is quoted directly from the Tor manual [archive]:
HiddenServiceDir DIRECTORY Store data files for a hidden service in DIRECTORY. Every hidden service must have a separate directory. You may use this option multiple times to specify multiple services. If DIRECTORY does not exist, Tor will create it. Please note that you cannot add new Onion Service to already running Tor instance if Sandbox is enabled.
HiddenServicePort VIRTPORT [TARGET] Configure a virtual port VIRTPORT for a hidden service. You may use this option multiple times; each time applies to the service using the most recent HiddenServiceDir. By default, this option maps the virtual port to the same port on 127.0.0.1 over TCP. You may override the target port, address, or both by specifying a target of addr, port, addr:port, or unix:path. (You can specify an IPv6 target as [addr]:port. Unix paths may be quoted, and may use standard C escapes.) You may also have multiple lines with the same VIRTPORT: when a user connects to that VIRTPORT, one of the TARGETs from those lines will be chosen at random. Note that address-port pairs have to be comma-separated.
Hidden VoIP Server
On Whonix-Gateway ™. Run the following command to watch both, vanguards and Tor's log output.
sudo journalctl -u vanguards -u tor@default -f
torsocks curl http://onionv3redacted.onion
curl output might include:
1593531192 ERROR torsocks: Host unreachable (in socks5_recv_connect_reply() at socks5.c:539) curl: (7) Couldn't connect to server
Tor vanguards log might include:
Possible Tor bug, or possible attack if very frequent: Got 1 dropped cell on circ 279088 (in state HS_SERVICE_REND HSSR_JOINED; old state HS_SERVICE_REND HSSR_CONNECTING) We force-closed circuit 281935 Tor bug #29699: Got 1 dropped cell on circ 281934 (in state HS_SERVICE_INTRO HSSI_ESTABLISHED; old state HS_SERVICE_INTRO HSSI_CONNECTING). We force-closed circuit 281934
- https://trac.torproject.org/projects/tor/ticket/29699 [archive] ( Tor: 0.4.3.x-final )
- https://trac.torproject.org/projects/tor/ticket/15618 [archive]
- https://github.com/mikeperry-tor/vanguards/blob/a214408c09ad092d415ff1a0e7fec135c30e609e/src/vanguards/bandguards.py [archive]
- https://github.com/mikeperry-tor/vanguards/issues/37 [archive]
- https://github.com/mikeperry-tor/vanguards/issues/37#issuecomment-472963014 [archive]
- https://trac.torproject.org/projects/tor/ticket/29700 [archive]
Tor Onion Services: Advanced Topics
Onion Services Security Enhancements
Over time, The Tor Project is steadily releasing additional features which enhance onion services security. Recent efforts to protect against guard enumeration attacks include the vanguards add-on and additional torrc options to pin the second and third hops of onion service circuits to a list of nodes. To learn more about these enhancements and their optional configuration, see:
- Announcing the Vanguards Add-On for Onion Services [archive]
- Vanguards GitHub resource [archive]
- vanguards - Additional protections for Tor Onion Services [archive]
- Onion Service Guard Protection - HSLayer2Nodes / HSLayer3Nodes [archive]
How Onion Services Connections Work
To understand how onion services work, a simple overview of the process is outlined below. 
Step 1. Onion services advertise their existence in the Tor network. This is done by randomly picking some relays and building circuits, before asking these relays to act as introduction points by providing the service's public key. The onion server's location (IP address) is shielded.
Step 2. The onion service generates an onion service descriptor containing the public key and a summary of introduction points. This is signed with its private key and then uploaded to a distributed hash table, so users can find the service when searching for a .onion resource.  This also forms an important verification mechanism for the user to confirm they are talking to the right onion service.
Step 3. The user who learnt that the .onion resource exists requests more information from the database, by downloading the descriptor from the distributed hash table. If the descriptor exists, the user now knows the introduction points and the right public key to use. The user also creates a Tor circuit to another randomly picked relay to use as a rendezvous point (with a one-time secret).
Step 4. If the descriptor is present and the rendezvous point is ready, the user assembles an "introduce message". This is encrypted to the onion service's public key and includes the rendezvous point address and the one-time secret. The user requests this be delivered to the onion service (via a Tor circuit) anonymously, so the IP address remains hidden.
Step 5. The onion service decrypts the user's introduce message and finds the rendezvous point address and one-time secret in it. The service creates a circuit to the rendezvous point and sends the one-time secret to it in a rendezvous message. The onion service must use the same set of entry guards when creating circuits, to prevent attackers from forcing onion services to use corrupt relays as an entry node (and learning the onion server's IP address via timing analysis).
Step 6. The rendezvous point notifies the user the successful connection has been established. Both the user and onion service use their circuits to the rendezvous point for communication. The rendezvous point relays end-to-end encrypted messages from user to service and vice versa.
Use of .onion addresses leads to a 6 relay arrangement: 3 picked by the user (with the third used as a rendezvous point), and 3 picked by the onion service. The final successful connection between a user and an onion service is represented in the picture below.
Figure: Alice (User) and Bob (Onion Service) Successful Connection 
Onion Services Security
It is difficult to confirm exactly how safe Tor onion services are. Therefore, this section is intended as a repository of relevant facts, quotes and links to provide an estimation -- feel free to add further germane material.
Hidden services are definitely weaker than regular Tor circuits, a) because the adversary can induce them to speak, and b) because they stay at the same place over time. Mostly 'a'.
That said, there are plenty of hidden services out there, and few stories of people breaking their anonymity by breaking Tor. So they're not foolproof for sure, but they're also not trivial to deanonymize.
I'll turn it around, and ask "easy compared to what?"
When you're a Tor client, you only use the Tor network when you choose to access it (e.g. by trying to fetch a web page). So if the attacker has some attack that works only a very small percentage of time, they have to wait for you to initiate connections.
But for a hidden service, they can cause you to initiate a connection just by visiting the hidden service. And they can do it as often as they want.
And then see http://freehaven.net/anonbib/#wpes12-cogs [archive] for a more recent example. The goal of that paper is to understand how long it takes in normal operation (with entry guards going offline and being replaced) before a typical user touches an adversary-controlled guard node. For simplicity, the paper assumes that you use your guards every minute of every day for however many weeks or months it takes. A realistic user doesn't do that, so the paper overestimates the risk. But a realistic hidden service *would* do that, if the adversary caused it to.
At the time of writing there are no known attacks used in the wild that consistently deanonymize Tor onion services. However, there is a plethora of Speculative Tor Attacks against the ecosystem that have been highlighted in research settings, including those that specifically target the server or client and server in combination. Therefore, Tor processes and anonymity protection might be seriously degraded under specific conditions.
A number of serious onion service concerns  have been mitigated since The Tor Project announced the release of v3 (
HiddenServiceVersion 3) onions in 2017, succeeding the original v2 onion service design, see: Tor's Fall Harvest: The Next Generation of Onion Services [archive].
Onion Service Authentication Client Setup
Notes about End-to-end Security of Onion Services
Hidden services are not really encrypted "end-to-end", they are only encrypted "Tor-to-end" (or "Tor-to-Tor"). The communication between the browser or server and Tor is sent in clear text. This does not really constitute a security issue, as localhost (or Workstation to Gateway on an isolated network), is supposed to be secure. But this does pose some security implications.
Firstly, with onion services alone and no TLS enabled, the adversary only needs to compromise Whonix-Gateway ™ to gain knowledge of the content of the connection and the client's identity/location. To compromise the content of the connection, the adversary only needs to compromise either the gateway or the workstation.
With both onion services and TLS enabled, an adversary needs to compromise Whonix-Workstation ™ to gain knowledge of the content of the connection. To gain knowledge of the client's identity/location, the adversary would have to compromise Whonix-Gateway ™ as well.
Although it is possible to use onion services and TLS in combination -- that is, https://****************.onion [archive] -- there are very few onion services reachable over TLS. For example, DuckDuckGo search engine https://duckduckgo.com/ [archive] can be reached over https://3g2upl4pq6kufc4m.onion/ [archive]. But since this only offers benefits to users of Whonix ™ (and other Tor gateway implementations), there is little demand. However, it does provide some nice defense in depth because it eliminates a single point of failure.
This does raise the question as to how the TLS certificate can be verified. That is a simple process for private sites where the server and clients know each other; they simply verify it over a pre-shared secure channel, for example a meeting.
In regards to public onion services, certificate authorities previously refused to give out certificates for .onion sites, for example Startssl.com declined because .onion is no .gTLD, see: Bug #6116: apply for .onion gTLD at IANA [archive]. However, in DuckDuckGo's case, a certificate has been issued by DigiCert which confirms TLS certificates can be issued for people who can reasonably prove they own a .onion domain. Presumably evidence of domain control may include editing its contents upon their request. Nevertheless, little faith should be placed in certificate authorities, see: Transport Layer Security (TLS).
Finally, it should be noted that running onion services with Whonix ™ is safer than running Tor and the server software on the same host, because even when misconfigured, there cannot be any IP or DNS leaks (by design).
High Traffic Onion Service Scalability Performance
Although mostly focused on non-anonymous onion services, the tor-dev mailing list discussion onionbalance useful on same server / for high-spec non-location hidden servers? [archive] contains interesting information on scalability and performance of high traffic onion services. The tor-dev mailing list [archive] (sign-up [archive]) is considered a useful resource for technical information since they are receptive to genuine inquiries.
- https://metrics.torproject.org/onionperf-throughput.html [archive]
- https://metrics.torproject.org/onionperf-latencies.html [archive]
- Hosting Location Hidden Services
- Onion Services Guides
- Remote Administration including SSH / VNC (x2go) into Whonix ™
- https://2019.www.torproject.org/docs/onion-services.html.en [archive]
- https://en.wikipedia.org/wiki/Secure_Sockets_Layer [archive]
- To be exact, only tor-to-tor, see Notes about End-to-end Security of Onion Services.
- http://www.quora.com/Is-there-an-SSL-equivalent-for-Tor-Hidden-Services [archive]
- https://archive.is/Aaqsz [archive]
- https://lists.torproject.org/pipermail/tor-talk/2016-October/042360.html [archive]
These applications are talking to Tor control port directed (filtered) through onion-grater, created through Tor control protocol command
- https://wiki.debian.org/WebServers [archive]
- It is advised to install libapache2-mod-removeip [archive].
- (Source: old forum [archive])
- https://tor.stackexchange.com/questions/17366/nginx-leaks-my-hidden-service-port-number [archive]
- https://tor.stackexchange.com/questions/15099/nginx-directory-disclosures [archive]
- https://scotthelme.co.uk/hardening-your-http-response-headers/ [archive]
- https://trac.nginx.org/nginx/ticket/523 [archive]
- https://mascherari.press/why-onionscan-should-worry-you/ [archive]
- https://mascherari.press/thwarting-identity-correlation-attacks/ [archive]
- https://github.com/camelids/ [archive]
- Website Fingerprinting Defenses at the Application Layer [archive]
- https://www.esat.kuleuven.be/cosic/?p=6743 [archive]
- https://forums.whonix.org/t/ship-or-document-ddos-resistant-torrc-settings/10417 [archive]
- Since it is easy to confirm that the internal LAN IP
10.152.152.10is normally used by Whonix-Gateway ™.
- Since Whonix ™ version 188.8.131.52.7
- The purpose of Onion Services Authentication has been asked about on the Tor Talk Mailing List [archive]. Answers:
To use yourself locally for testing on the same Whonix-Gateway ™.
On the Whonix-Gateway ™.
Run as user. Do not run as root.
cp /var/lib/tor_autogen/hidden_service/1.auth_private ~/
- https://www.torproject.org/docs/hidden-services.html.en [archive]
- This is currently a 16 character name, but will be increased to 54 characters in the near-medium term to upgrade the cryptographic strength of .onion services. See: https://blog.torproject.org/blog/cooking-onions-names-your-onions [archive]
- https://www.torproject.org/images/THS-6.png [archive]
- Concerns with v2 onion services included:
- 80 bit name hash and RSA-1024 sized keys
- Quote Mike Perry (https://www.torproject.org/about/corepeople.html.en [archive]): http://email@example.com/msg05418.html [archive]
- Quote Mike Perry: http://firstname.lastname@example.org/msg05462.html [archive]
- Also see: The Tor Project Blog: Onion Services need some love [archive].
- Non-Hidden Onion Services Considered Harmful: Attacks and Detection [archive]
- https://forums.whonix.org/t/cryptolog-for-whonix-website/3369/12 [archive]
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