Tuesday, 7 December 2021

Don't use Tor for Bitcoin

For some time now, I've been getting reports from customers that Bitcoin mixers are stealing their coins. I now have a pretty good guess what's happening:

It's common for Bitcoiners to use Tor to anonymize their activity. Unfortunately, this has a major risk.

For several years now, an unknown attacker has been running malicious Tor nodes to steal users Bitcoin: https://nusenu.medium.com/how-malicious-tor-relays-are-exploiting-users-in-2020-part-i-1097575c0cac

Here is how the attack works:

  1. Attacker creates many Tor exit nodes so that up to a third of Tor nodes are operated by them.
  2. Attacker looks for HTTP requests to crypto sites, especially Bitcoin mixers. Nearly all crypto sites are HTTPS, but users usually do not type HTTPS:// before a web address. Instead, they type the domain name and let the website redirect from HTTP to HTTPS. The attacker strips out this redirect.
  3. Because the website session is in plaintext, the attacker can dynamically replace Bitcoin addresses to his own.
  4. Bitcoin deposits are redirected to the attacker. The victims blame the coin mixer.

Solutions:

  1. Website operators should use HSTS Preloading (https://hstspreload.org/). Most crypto websites do NOT currently do this.
  2. Users should install HTTPS Everywhere https://www.eff.org/https-everywhere
  3. Users should check that websites connections are HTTPS:// Browser are getting better are warning about HTTP connections
  4. Don't use Tor for crypto. Use a VPN instead. You can pay for many VPN's with Bitcoin. Of course, you must trust that the VPN is non-malicious too.
submitted by /u/HeroicLife
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