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One on One large file sharing (Syncthing over Tor)

Onionshare is a good choice when you want to share small files over tor. But onionshare cannot handle big files, because when tor circuit fails (which is quite common in Tor) your download simply fails, and it does not support resuming the download at where it previously failed. Syncthing is a better alternative if you want to share large files over tor, it does not need any setup or hosting, and it will automatically retry at break point when network fails.

Syncthing is FOSS software and has E2EE by default, and can run it without requiring a VPS. This means you can just spin up syncthing client from your whonix workstation directly, and your data will be encrypted and sent through public syncthing nodes. If you have a threat model that needs a way to reliably share files with minimum exposure, this setup suits the need.

Syncthing has its own relays for supporting transmission of files between peers which are both behind the nat, and it works when both parties are behind tor. This allows us to guarantee the anonymity of both parties.

OPSEC Recommendations:

1. Hardware : (Personal Computer / Laptop)

2. Host OS: Linux (Or Qubes OS)

3. Hypervisor: libvirtd QEMU/KVM (Or Qubes OS's Xen)

4. Virtual Machine: Whonix

It is highly recommended to use whonix for this setup, because there are always cases that an app might not honor your proxy setting and somehow tries to connect to the syncthing relay directly without going through Tor. It is always a good idea to put any anonymous use app in a whonix workstation, so your clearnet ip doesn't get revealed.

Sidenote: Help us improve this tutorial by letting us know if there's anything missing or incorrect on this git issue directly!

Initial Setup

The first thing to do is to get syncthing to your whonix workstation.

For simplicity you can just do

sudo apt-get install syncthing -y

If apt does not contain the up to date package, then you need to get it from the syncthing website

Next verify the sha256sum according to https://syncthing.net/security/

curl -s https://syncthing.net/release-key.txt | gpg --import

Check the gpg fingerprint, it should be like this

gpg --fingerprint
/home/user/.gnupg/pubring.kbx
-----------------------------
pub   rsa2048/0xD26E6ED000654A3E 2014-12-29 [SC]
		Key fingerprint = 37C8 4554 E7E0 A261 E4F7  6E1E D26E 6ED0 0065 4A3E
uid                   [ unknown] Syncthing Release Management 
sub   rsa2048/0x681C3CFCF614F575 2014-12-29 [E]

Then download verify the checksum file, and check the checksum to see if it matches

$ curl -sLO https://github.com/syncthing/syncthing/releases/download/v1.23.6/sha256sum.txt.asc	

$ gpg --verify sha256sum.txt.asc
gpg: Signature made Mo 03 Jul 2023 10:09:30 UTC
gpg:                using RSA key D26E6ED000654A3E
gpg: Good signature from "Syncthing Release Management "
gpg: WARNING: This key is not certified with a trusted signature!
gpg:          There is no indication that the signature belongs to the owner.	

$ sha256sum -c sha256sum.txt.asc
...
sha256sum: syncthing-linux-386-v1.23.6.tar.gz: No such file or directory
syncthing-linux-386-v1.23.6.tar.gz: FAILED open or read
syncthing-linux-amd64-v1.23.6.tar.gz: OK
sha256sum: syncthing-linux-armv5-v1.23.6.tar.gz: No such file or directory
syncthing-linux-armv5-v1.23.6.tar.gz: FAILED open or read
...
sha256sum: WARNING: 14 lines are improperly formatted
sha256sum: WARNING: 35 listed files could not be read

Next you need to do some changes in the tor browser, so you can access the web panel that is running on localhost (127.0.0.1), type about:config inside the address bar, accept the risk and continue:

search for no_proxies_on in the search bar, and add 127.0.0.1 to it

Editing your tor browser is fine if you are just using it to access local syncthing instance, but you should revert the change if you want to access the internet. Changing tor config might bring some unexpected browser fingerprint issue. You should get a separate whonix vm if paranoid.

How to setup syncthing

Next decompress the syncthing pack and execute it

$ tar xvf syncthing-linux-amd64-v1.28.0.tar.gz

$ cd syncthing-linux-amd64-v1.28.0/

$ ./syncthing

If you have setup your tor browser correctly it should automatically redirect you to http://127.0.0.1:8384/ and you will see the web panel

Next thing to do is to find your client id, it is in the actions menu

Next exchange this id with people you are sharing file with

After that add each other in both clients in the remote device section, if nothing goes wrong you should be able to see each other in the remote device section showed as "connected"

How to sync files anonymously

After the previous setup, you can share the file you want. But be aware tor traffic has low bandwidth, that is the price of online Anonymity! Because if both parties are behind tor, your file goes through a circuit like this:

I personally tried this setup, to send a 10GB file it took me 4 hours 30 minutes to send it, which is normal due to the Tor network being slow, you'll need to be patient when you are trying to send large files over Tor.

You and your peer will only see the relay server's ip address, unlike the vpn setup which will expose the vpn ip you are using, which you can check here

You peer also won't know you are using tor if you do not tell him

Choose add folder to create a new sharing Folder, and choose to share this folder with your peer

If nothing goes wrong, the receiver should see this

Agree and add the folder, after that syncthing will automatically transmit the files