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/files.md

@@ -56,7 +56,7 @@ Subdirectory       | File(s)               | Description
 `./`               | `fee_estimates.dat`   | Stores statistics used to estimate minimum transaction fees and priorities required for confirmation
 `./`               | `guisettings.ini.bak` | Backup of former [GUI settings](#gui-settings) after `-resetguisettings` option is used
 `./`               | `mempool.dat`         | Dump of the mempool's transactions
-`./`               | `onion_private_key`   | Cached Tor onion service private key for `-listenonion` option
+`./`               | `onion_v3_private_key` | Cached Tor onion service private key for `-listenonion` option
 `./`               | `peers.dat`           | Peer IP address database (custom format)
 `./`               | `settings.json`       | Read-write settings set through GUI or RPC interfaces, augmenting manual settings from [bitcoin.conf](bitcoin-conf.md). File is created automatically if read-write settings storage is not disabled with `-nosettings` option. Path can be specified with `-settings` option
 `./`               | `.cookie`             | Session RPC authentication cookie; if used, created at start and deleted on shutdown; can be specified by `-rpccookiefile` option
@@ -98,6 +98,7 @@ Path           | Description | Repository notes
 `blkindex.dat` | Blockchain index BDB database; replaced by {`chainstate/`, `blocks/index/`, `blocks/revNNNNN.dat`<sup>[\[2\]](#note2)</sup>} in 0.8.0 | [PR #1677](https://github.com/bitcoin/bitcoin/pull/1677)
 `blk000?.dat`  | Block data (custom format, 2 GiB per file); replaced by `blocks/blkNNNNN.dat`<sup>[\[2\]](#note2)</sup> in 0.8.0 | [PR #1677](https://github.com/bitcoin/bitcoin/pull/1677)
 `addr.dat`     | Peer IP address BDB database; replaced by `peers.dat` in [0.7.0](https://github.com/bitcoin/bitcoin/blob/master/doc/release-notes/release-notes-0.7.0.md) | [PR #1198](https://github.com/bitcoin/bitcoin/pull/1198), [`928d3a01`](https://github.com/bitcoin/bitcoin/commit/928d3a011cc66c7f907c4d053f674ea77dc611cc)
+`onion_private_key` | Cached Tor onion service private key for `-listenonion` option. Was used for Tor v2 services; replaced by `onion_v3_private_key` in [0.21.0](https://github.com/bitcoin/bitcoin/blob/master/doc/release-notes/release-notes-0.21.0.md) | [PR #19954](https://github.com/bitcoin/bitcoin/pull/19954)
 
 ## Notes
 

doc/release-notes.md

@@ -82,6 +82,17 @@ P2P and network changes
   node using P2P relay. This version reduces the initial broadcast guarantees
   for wallet transactions submitted via P2P to a node running the wallet. (#18038)
 
+- 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. Bitcoin 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)
+
 Updated RPCs
 ------------
 

src/torcontrol.cpp

@@ -532,8 +532,9 @@ void TorController::auth_cb(TorControlConnection& _conn, const TorControlReply&
         }
 
         // Finally - now create the service
-        if (private_key.empty()) // No private key, generate one
+        if (private_key.empty()) { // No private key, generate one
-            private_key = "NEW:RSA1024"; // Explicitly request RSA1024 - see issue #9214
+            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()),
@@ -718,7 +719,7 @@ 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)