From d24401ada8604dae53c145f6738831adc9362690 Mon Sep 17 00:00:00 2001
From: Sosthene00 <674694@protonmail.ch>
Date: Wed, 17 Apr 2024 08:27:46 +0200
Subject: [PATCH] Add AnkSharedSecret

---
 src/crypto.rs | 55 ++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 50 insertions(+), 5 deletions(-)

diff --git a/src/crypto.rs b/src/crypto.rs
index 3873b1d..71eb324 100644
--- a/src/crypto.rs
+++ b/src/crypto.rs
@@ -6,26 +6,71 @@ use sp_backend::{
         consensus::serde::hex,
         hex::DisplayHex,
         key::constants::SECRET_KEY_SIZE,
-        secp256k1::{ecdh::SharedSecret, SecretKey},
+        secp256k1::{ecdh::SharedSecret, PublicKey, SecretKey},
         Txid,
     },
-    silentpayments::sending::SilentPaymentAddress,
+    silentpayments::{
+        sending::SilentPaymentAddress, 
+        bitcoin_hashes::{sha256t_hash_newtype, HashEngine, Hash}
+    },
 };
 
 use serde::{Deserialize, Serialize};
 use serde_json::{json, Value};
 
 use aes_gcm::{
-    aead::{Aead, AeadInPlace, KeyInit, Nonce},
-    AeadCore, Aes256Gcm, AesGcm, Key, TagSize,
-    aes::{Aes256, cipher::{generic_array::GenericArray, consts::{U32, U8}}},
+    aead::{Aead, AeadInPlace, Nonce},
+    aes::{
+        cipher::{
+            consts::{U32, U8},
+            generic_array::GenericArray,
+        },
+        Aes256,
+    },
+    AesGcm, Key, TagSize,
 };
+pub use aes_gcm::{AeadCore, Aes256Gcm, KeyInit};
 use rand::thread_rng;
 
 const HALFKEYSIZE: usize = SECRET_KEY_SIZE / 2;
 
 const THIRTYTWO: usize = 32;
 
+type SharedPublicKey = PublicKey;
+
+#[derive(Debug)]
+pub struct AnkSharedSecret(SharedSecret);
+
+impl AnkSharedSecret {
+    pub fn new_from_public_key(public_key: SharedPublicKey) -> Self {
+        let t_hash = SharedPublicKeyHash::from_shared_pubkey(public_key);
+        Self(SharedSecret::from_bytes(t_hash.to_byte_array()))
+    }
+
+    pub fn to_byte_array(&self) -> [u8;SECRET_KEY_SIZE] {
+        self.0.secret_bytes()
+    }
+
+    pub fn to_string(&self) -> String {
+        format!("{}", self.0.display_secret())
+    }
+}
+
+sha256t_hash_newtype! {
+    pub struct SharedPublicKeyTag = hash_str("4nk/SharedPublicKey");
+
+    #[hash_newtype(forward)]
+    pub struct SharedPublicKeyHash(_);
+}
+
+impl SharedPublicKeyHash {
+    pub fn from_shared_pubkey(shared_pubkey: SharedPublicKey) -> Self {
+        let mut eng = SharedPublicKeyHash::engine();
+        eng.input(&shared_pubkey.serialize());
+        SharedPublicKeyHash::from_engine(eng)
+    }
+}
+
 pub struct HalfKey([u8; HALFKEYSIZE]);
 
 impl TryFrom<Vec<u8>> for HalfKey {