From 3194cb2d561882ba2f5d3d7736371a2c3c29bb53 Mon Sep 17 00:00:00 2001
From: cygnet <cygnet3@proton.me>
Date: Sun, 23 Jul 2023 14:15:45 +0200
Subject: [PATCH] Extract calculate functions from scanning function

---
 src/main.rs      |  4 ++--
 src/receiving.rs | 56 +++++++++++++++++++++++++++++++-----------------
 2 files changed, 38 insertions(+), 22 deletions(-)

diff --git a/src/main.rs b/src/main.rs
index 0a92ad9..923a00f 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -89,7 +89,7 @@ fn main() {
 
             // todo labels
 
-            let outputs_to_check: Vec<XOnlyPublicKey> = given
+            let mut outputs_to_check: Vec<XOnlyPublicKey> = given
                 .outputs
                 .iter()
                 .map(|x| XOnlyPublicKey::from_str(x).unwrap())
@@ -104,7 +104,7 @@ fn main() {
                 B_spend,
                 A_sum,
                 outpoints_hash,
-                outputs_to_check,
+                &mut outputs_to_check,
                 labels,
             );
 
diff --git a/src/receiving.rs b/src/receiving.rs
index b66acbf..46e0784 100644
--- a/src/receiving.rs
+++ b/src/receiving.rs
@@ -66,6 +66,38 @@ pub fn encode_silent_payment_address(
     bech32::encode(hrp, data, bech32::Variant::Bech32m).unwrap()
 }
 
+fn calculate_P_n(B_spend: &PublicKey, t_n: [u8; 32] ) -> XOnlyPublicKey {
+    let secp = Secp256k1::new();
+
+    let G: PublicKey = SecretKey::from_slice(&Scalar::ONE.to_be_bytes())
+        .unwrap()
+        .public_key(&secp);
+    let intermediate = G
+        .mul_tweak(&secp, &Scalar::from_be_bytes(t_n).unwrap())
+        .unwrap();
+    let P_n = intermediate.combine(&B_spend).unwrap();
+    let (P_n_xonly, _) = P_n.x_only_public_key();
+
+    P_n_xonly
+}
+
+fn calculate_t_n(ecdh_shared_secret: &[u8; 33], n: u32) -> [u8; 32] {
+    let mut bytes: Vec<u8> = Vec::new();
+    bytes.extend_from_slice(ecdh_shared_secret);
+    bytes.extend_from_slice(&ser_uint32(n));
+    sha256(&bytes)
+}
+
+fn calculate_ecdh_secret(A_sum: &PublicKey, b_scan: SecretKey, outpoints_hash: [u8; 32]) -> [u8; 33] {
+    let secp = Secp256k1::new();
+
+    let intermediate = A_sum.mul_tweak(&secp, &b_scan.into()).unwrap();
+    let scalar = Scalar::from_be_bytes(outpoints_hash).unwrap();
+    let ecdh_shared_secret = intermediate.mul_tweak(&secp, &scalar).unwrap().serialize();
+
+    ecdh_shared_secret
+}
+
 #[derive(Debug)]
 pub struct WalletItem {
     pub pub_key: String,
@@ -77,29 +109,13 @@ pub fn scanning(
     B_spend: PublicKey,
     A_sum: PublicKey,
     outpoints_hash: [u8; 32],
-    outputs_to_check: Vec<XOnlyPublicKey>,
+    outputs_to_check: &mut Vec<XOnlyPublicKey>,
     _labels: &HashMap<String, u32>,
 ) -> Vec<WalletItem> {
-    let secp = Secp256k1::new();
-
-    let intermediate = A_sum.mul_tweak(&secp, &b_scan.into()).unwrap();
-    let scalar = Scalar::from_be_bytes(outpoints_hash).unwrap();
-    let ecdh_shared_secret = intermediate.mul_tweak(&secp, &scalar).unwrap().serialize();
-
+    let ecdh_shared_secret =  calculate_ecdh_secret(&A_sum, b_scan, outpoints_hash);
     let n = 0;
-    let mut bytes: Vec<u8> = Vec::new();
-    bytes.extend_from_slice(&ecdh_shared_secret);
-    bytes.extend_from_slice(&ser_uint32(n));
-    let t_n = sha256(&bytes);
-
-    let G: PublicKey = SecretKey::from_slice(&Scalar::ONE.to_be_bytes())
-        .unwrap()
-        .public_key(&secp);
-    let intermediate = G
-        .mul_tweak(&secp, &Scalar::from_be_bytes(t_n).unwrap())
-        .unwrap();
-    let P_n = intermediate.combine(&B_spend).unwrap();
-    let (P_n_xonly, _) = P_n.x_only_public_key();
+    let t_n = calculate_t_n(&ecdh_shared_secret, n);
+    let P_n_xonly = calculate_P_n(&B_spend, t_n);
 
     let mut wallet: Vec<WalletItem> = vec![];
     for output in outputs_to_check {