Documentation: Out of date Tor v2 onion address

[daira]

Split from #6742 by @metalworker2 :

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I found these issues in the docs when I was following the instructions for installing on Debian/Ubuntu officially supported platform:

https://zcash.readthedocs.io/en/latest/rtd_pages/install_debian_bin_packages.html

Out of date onion address version

The repository is also accessible via Tor, after installing the apt-transport-tor package, at the address zcaptnv5ljsxpnjt.onion

However, if I visit this website in Tor browser, then I am met with an error message:

The provided onionsite address is invalid. Please check that you entered it correctly.

Details: 0xF6 — The provided .onion address is invalid. This error is returned due to one of the following reasons: the address checksum doesn't match, the ed25519 public key is invalid, or the encoding is invalid.

Upon closer inspection I see that the given onion address is a Tor v2 address. According to the Tor project website:

V2 onion addresses are fundamentally insecure. If you have a v2 onion, we recommend you migrate now. This is a backward incompatible change: v2 onion services will not be reachable after September 2021.

https://support.torproject.org/onionservices/v2-deprecation/

So this documentation is almost 2 years out of date! See related #6075

[darkerego]

A workaround for those running lightwalletd in front of zec is to simply forward a v3 onion service to the lightwalletd port. That works fine for the moment for my use case.