feat: bring up to date with remote signer spec

remote unused comment

change expiry

run clippy

run fmt

fix tests

Author: lescuer97

crates/cashu/src/nuts/nut00/mod.rs

@@ -9,6 +9,7 @@ use std::hash::{Hash, Hasher};
 use std::str::FromStr;
 use std::string::FromUtf8Error;
 
+use bitcoin::hashes::{sha256, Hash as BitcoinHash};
 use serde::{de, Deserialize, Deserializer, Serialize};
 use thiserror::Error;
 
@@ -577,16 +578,12 @@ pub enum CurrencyUnit {
 
 #[cfg(feature = "mint")]
 impl CurrencyUnit {
-    /// Derivation index mint will use for unit
-    pub fn derivation_index(&self) -> Option<u32> {
-        match self {
-            Self::Sat => Some(0),
-            Self::Msat => Some(1),
-            Self::Usd => Some(2),
-            Self::Eur => Some(3),
-            Self::Auth => Some(4),
-            _ => None,
-        }
+    ///  Big endian encoded integer of the first 4 bytes of the sha256 hash of the unit string.
+    pub fn derivation_index(&self) -> u32 {
+        let unit_str = self.to_string().to_lowercase();
+        let bytes = <sha256::Hash as BitcoinHash>::hash(unit_str.as_bytes());
+        // Take the first 4 bytes and convert to u32 (big endian) make sure the integer
+        u32::from_be_bytes([bytes[0], bytes[1], bytes[2], bytes[3]]) & !(1 << 31)
     }
 }
 
@@ -993,6 +990,30 @@ mod tests {
         assert_eq!(unit, deserialized)
     }
 
+    #[test]
+    fn four_bytes_hash_currency_unit() {
+        let unit = CurrencyUnit::Sat;
+        let index = unit.derivation_index();
+        assert_eq!(index, 866057899);
+
+        let unit = CurrencyUnit::Msat;
+        let index = unit.derivation_index();
+        assert_eq!(index, 1980671987);
+
+        let unit = CurrencyUnit::Eur;
+        let index = unit.derivation_index();
+        assert_eq!(index, 975082952);
+
+        let unit = CurrencyUnit::Usd;
+        let index = unit.derivation_index();
+        assert_eq!(index, 1443872135);
+
+        let unit = CurrencyUnit::Auth;
+        let index = unit.derivation_index();
+
+        assert_eq!(index, 1039440956)
+    }
+
     #[test]
     fn test_payment_method_parsing() {
         // Test standard variants

crates/cdk-signatory/src/common.rs

@@ -159,11 +159,11 @@ pub fn create_new_keyset<C: secp256k1::Signing>(
 }
 
 pub fn derivation_path_from_unit(unit: CurrencyUnit, index: u32) -> Option<DerivationPath> {
-    let unit_index = unit.derivation_index()?;
+    let unit_index = unit.derivation_index();
 
     Some(DerivationPath::from(vec![
-        ChildNumber::from_hardened_idx(0).expect("0 is a valid index"),
-        ChildNumber::from_hardened_idx(unit_index).expect("0 is a valid index"),
+        ChildNumber::from_hardened_idx(129372).expect("129372 is a valid index"),
+        ChildNumber::from_hardened_idx(unit_index).expect("unit index should be valid"),
         ChildNumber::from_hardened_idx(index).expect("0 is a valid index"),
     ]))
 }