signer: Change derivation key for master rune

We change the derivation key for the master rune to be closer to what
core-lightning is using. We need to be very careful not to use the same
derivation key though to avoid the possibility to create runes from the
node instead from the signer.

Signed-off-by: Peter Neuroth <[email protected]>

libs/gl-client/src/signer/mod.rs

@@ -43,6 +43,8 @@ mod resolve;
 const VERSION: &str = "v23.08";
 const GITHASH: &str = env!("GIT_HASH");
 const RUNE_VERSION: &str = "gl0";
+// This is the same derivation key that is used by core lightning itself.
+const RUNE_DERIVATION_SECRET: &str = "gl-commando";
 
 #[derive(Clone)]
 pub struct Signer {
@@ -166,7 +168,7 @@ impl Signer {
 
         // Init master rune. We create the rune seed from the nodes
         // seed by deriving a hardened key tagged with "rune secret".
-        let rune_secret = crypto_utils::hkdf_sha256(&sec, "rune secret".as_bytes(), &[]);
+        let rune_secret = crypto_utils::hkdf_sha256(&sec, RUNE_DERIVATION_SECRET.as_bytes(), &[]);
         let mr = Rune::new_master_rune(&rune_secret, vec![], None, Some(RUNE_VERSION.to_string()))?;
 
         trace!("Initialized signer for node_id={}", hex::encode(&id));