Derive Tor secret key from seed.

Cargo.lock

@@ -3742,6 +3742,7 @@ dependencies = [
  "dialoguer",
  "directories-next",
  "ecdsa_fun",
+ "ed25519-dalek",
  "futures",
  "get-port",
  "hyper 0.14.7",

swap/Cargo.toml

@@ -26,6 +26,7 @@ data-encoding = "2.3"
 dialoguer = "0.8"
 directories-next = "2"
 ecdsa_fun = { git = "https://github.com/LLFourn/secp256kfun", features = ["libsecp_compat", "serde"] }
+ed25519-dalek = "1"
 futures = { version = "0.3", default-features = false }
 itertools = "0.10"
 libp2p = { version = "0.37", default-features = false, features = ["tcp-tokio", "yamux", "mplex", "dns-tokio", "noise", "request-response", "websocket"] }

swap/src/seed.rs

@@ -12,6 +12,7 @@ use std::fmt;
 use std::fs::{self, File};
 use std::io::{self, Write};
 use std::path::{Path, PathBuf};
+use torut::onion::TorSecretKeyV3;
 
 pub const SEED_LENGTH: usize = 32;
 
@@ -47,6 +48,14 @@ impl Seed {
         identity::Keypair::Ed25519(key.into())
     }
 
+    pub fn derive_torv3_key(&self) -> TorSecretKeyV3 {
+        let bytes = self.derive(b"TOR").bytes();
+        let sk = ed25519_dalek::SecretKey::from_bytes(&bytes)
+            .expect("Failed to create a new extended secret key for Tor.");
+        let esk = ed25519_dalek::ExpandedSecretKey::from(&sk);
+        esk.to_bytes().into()
+    }
+
     pub fn from_file_or_generate(data_dir: &Path) -> Result<Self, Error> {
         let file_path_buf = data_dir.join("seed.pem");
         let file_path = Path::new(&file_path_buf);