tor: make a TORv3 hidden service instead of TORv2

TORv2 is deprecated [1], thus whenever we create the hidden service
ourselves create a TORv3 one instead.

[1] https://blog.torproject.org/v2-deprecation-timeline

doc/release-notes.md

@@ -284,6 +284,19 @@ It enforces the same rules as the legacy cold-staking opcode, but without allowi
 The new opcode takes the name of `OP_CHECKCOLDSTAKEVERIFY`, and the legacy opcode (`0xd1`) is renamed to `OP_CHECKCOLDSTAKEVERIFY_LOF` (last-output-free).
 Scripts with the old opcode are still accepted on the network (the restriction on the last-output is enforced after the script validation in this case), but the client creates new delegations with the new opcode, by default, after the upgrade enforcement.
 
+P2P and network changes
+-----------------------
+
+- The Tor onion service that is automatically created by setting the
+  `-listenonion` configuration parameter will now be created as a Tor v3 service
+  instead of Tor v2. The private key that was used for Tor v2 (if any) will be
+  left untouched in the `onion_private_key` file in the data directory (see
+  `-datadir`) and can be removed if not needed. PIVX Core will no longer
+  attempt to read it. The private key for the Tor v3 service will be saved in a
+  file named `onion_v3_private_key`. To use the deprecated Tor v2 service (not
+  recommended), then `onion_private_key` can be copied over
+  `onion_v3_private_key`, e.g.
+  `cp -f onion_private_key onion_v3_private_key`. (#19954)
 
 Multi-wallet support
 --------------------

src/torcontrol.cpp

@@ -535,9 +535,10 @@ void TorController::auth_cb(TorControlConnection& _conn, const TorControlReply&
         }
 
         // Finally - now create the service
-        if (private_key.empty()) // No private key, generate one
-            private_key = "NEW:RSA1024"; // Explicitly request RSA1024 - see issue #9214
-        // Request hidden service, redirect port.
+        if (private_key.empty()) { // No private key, generate one
+            private_key = "NEW:ED25519-V3"; // Explicitly request key type - see issue #9214
+        }
+        // Request onion service, redirect port.
         // Note that the 'virtual' port is always the default port to avoid decloaking nodes using other ports.
         _conn.Command(strprintf("ADD_ONION %s Port=%i,127.0.0.1:%i", private_key, Params().GetDefaultPort(), GetListenPort()),
             std::bind(&TorController::add_onion_cb, this, std::placeholders::_1, std::placeholders::_2));
@@ -721,7 +722,7 @@ void TorController::Reconnect()
 
 fs::path TorController::GetPrivateKeyFile()
 {
-    return GetDataDir() / "onion_private_key";
+    return GetDataDir() / "onion_v3_private_key";
 }
 
 void TorController::reconnect_cb(evutil_socket_t fd, short what, void *arg)