From 8013667b58f6a2c142757212735d5710a786ac6b Mon Sep 17 00:00:00 2001
From: Sergi Delgado Segura <sergi.delgado.s@gmail.com>
Date: Tue, 16 Mar 2021 15:55:44 +0100
Subject: [PATCH] Adds lighting message signing/verification/pk_recovery

---
 lightning/src/lib.rs                  |  2 +
 lightning/src/util/message_signing.rs | 90 +++++++++++++++++++++++++++
 lightning/src/util/mod.rs             |  1 +
 3 files changed, 93 insertions(+)
 create mode 100644 lightning/src/util/message_signing.rs

diff --git a/lightning/src/lib.rs b/lightning/src/lib.rs
index 567a7e186..59a714295 100644
--- a/lightning/src/lib.rs
+++ b/lightning/src/lib.rs
@@ -31,6 +31,8 @@
 #[cfg(all(test, feature = "unstable"))] extern crate test;
 
 extern crate bitcoin;
+
+
 #[cfg(any(test, feature = "_test_utils"))] extern crate hex;
 #[cfg(any(test, feature = "fuzztarget", feature = "_test_utils"))] extern crate regex;
 
diff --git a/lightning/src/util/message_signing.rs b/lightning/src/util/message_signing.rs
new file mode 100644
index 000000000..528855835
--- /dev/null
+++ b/lightning/src/util/message_signing.rs
@@ -0,0 +1,90 @@
+use crate::util::zbase32;
+use bitcoin::hashes::{sha256d, Hash};
+use bitcoin::secp256k1::recovery::{RecoverableSignature, RecoveryId};
+use bitcoin::secp256k1::{Error, Message, PublicKey, Secp256k1, SecretKey};
+
+static LN_MESSAGE_PREFIX: &[u8] = "Lightning Signed Message:".as_bytes();
+
+
+fn sigrec_encode(sig_rec: RecoverableSignature) -> Vec<u8> {
+    let (rid, rsig) = sig_rec.serialize_compact();
+    let prefix = rid.to_i32() as u8 + 31;
+
+    [&[prefix], &rsig[..]].concat()
+}
+
+
+fn sigrec_decode(sig_rec: Vec<u8>) -> Result<RecoverableSignature, Error> {
+    let rsig = &sig_rec[1..];
+    let rid = sig_rec[0] as i32 - 31;
+    
+    match RecoveryId::from_i32(rid) {
+        Ok(x) => RecoverableSignature::from_compact(rsig, x),
+        Err(e) => Err(e)
+    }
+}
+
+
+pub fn sign(msg: &[u8], sk: SecretKey) -> Result<String, Error> {
+    let secp_ctx = Secp256k1::signing_only();
+    let msg_hash = sha256d::Hash::hash(&[LN_MESSAGE_PREFIX, msg].concat());
+
+    let sig = secp_ctx.sign_recoverable(&Message::from_slice(&msg_hash)?, &sk);
+    Ok(zbase32::encode(&sigrec_encode(sig)))
+}
+
+pub fn recover_pk(msg: &[u8], sig: String) ->  Result<PublicKey, Error>{
+    let secp_ctx = Secp256k1::verification_only();
+    let msg_hash = sha256d::Hash::hash(&[LN_MESSAGE_PREFIX, msg].concat());
+
+    match zbase32::decode(&sig) {
+        Ok(sig_rec) => {
+            match sigrec_decode(sig_rec) {
+                Ok(sig) => secp_ctx.recover(&Message::from_slice(&msg_hash)?, &sig),
+                Err(e) => Err(e)
+            }
+        },
+        Err(_) => Err(Error::InvalidSignature)
+    }
+    
+}
+
+pub fn verify(msg: &[u8], sig: String, pk: PublicKey) -> bool {
+    match recover_pk(msg, sig) {
+        Ok(x) => x == pk,
+        Err(_) => false
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use util::message_signing::{sign, recover_pk, verify};
+    use bitcoin::secp256k1::key::ONE_KEY;
+    use bitcoin::secp256k1::{PublicKey, Secp256k1};
+    
+    #[test]
+    fn test_sign() {
+        let message = "test message";
+        let zbase32_sig = sign(message.as_bytes(), ONE_KEY);
+
+        assert_eq!(zbase32_sig.unwrap(), "d9tibmnic9t5y41hg7hkakdcra94akas9ku3rmmj4ag9mritc8ok4p5qzefs78c9pqfhpuftqqzhydbdwfg7u6w6wdxcqpqn4sj4e73e")
+    }
+
+    #[test]
+    fn test_recover_pk() {
+        let message = "test message";
+        let sig = "d9tibmnic9t5y41hg7hkakdcra94akas9ku3rmmj4ag9mritc8ok4p5qzefs78c9pqfhpuftqqzhydbdwfg7u6w6wdxcqpqn4sj4e73e";
+        let pk = recover_pk(message.as_bytes(), String::from(sig));
+
+        assert_eq!(pk.unwrap(), PublicKey::from_secret_key(&Secp256k1::signing_only(), &ONE_KEY))
+    }
+
+    #[test]
+    fn test_verify() {
+        let message = "another message";
+        let sig = sign(message.as_bytes(), ONE_KEY).unwrap();
+        let pk = PublicKey::from_secret_key(&Secp256k1::signing_only(), &ONE_KEY);
+
+        assert!(verify(message.as_bytes(), String::from(sig), pk))
+    }
+}
diff --git a/lightning/src/util/mod.rs b/lightning/src/util/mod.rs
index 59b46a4f1..761d1fd02 100644
--- a/lightning/src/util/mod.rs
+++ b/lightning/src/util/mod.rs
@@ -16,6 +16,7 @@ pub mod events;
 pub mod errors;
 pub mod ser;
 pub mod zbase32;
+pub mod message_signing;
 
 pub(crate) mod byte_utils;
 pub(crate) mod chacha20;
-- 
2.39.5