diff --git a/crates/cdk/src/nuts/nut01/mod.rs b/crates/cdk/src/nuts/nut01/mod.rs
index 649e1ed9..c23f7936 100644
--- a/crates/cdk/src/nuts/nut01/mod.rs
+++ b/crates/cdk/src/nuts/nut01/mod.rs
@@ -37,16 +37,20 @@ pub enum Error {
     },
 }
 
-/// Mint Keys [NUT-01]
+/// Mint public keys per amount.
+///
+/// This is a variation of [MintKeys] that only exposes the public keys.
+///
+/// See [NUT-01]
 #[derive(Debug, Clone, PartialEq, Eq, Deserialize, Serialize)]
-pub struct Keys(BTreeMap<String, PublicKey>);
+pub struct Keys(BTreeMap<Amount, PublicKey>);
 
 impl From<MintKeys> for Keys {
     fn from(keys: MintKeys) -> Self {
         Self(
             keys.0
-                .iter()
-                .map(|(amount, keypair)| (amount.to_string(), keypair.public_key))
+                .into_iter()
+                .map(|(amount, keypair)| (amount, keypair.public_key))
                 .collect(),
         )
     }
@@ -55,25 +59,25 @@ impl From<MintKeys> for Keys {
 impl Keys {
     /// Create new [`Keys`]
     #[inline]
-    pub fn new(keys: BTreeMap<String, PublicKey>) -> Self {
+    pub fn new(keys: BTreeMap<Amount, PublicKey>) -> Self {
         Self(keys)
     }
 
     /// Get [`Keys`]
     #[inline]
-    pub fn keys(&self) -> &BTreeMap<String, PublicKey> {
+    pub fn keys(&self) -> &BTreeMap<Amount, PublicKey> {
         &self.0
     }
 
     /// Get [`PublicKey`] for [`Amount`]
     #[inline]
     pub fn amount_key(&self, amount: Amount) -> Option<PublicKey> {
-        self.0.get(&amount.to_string()).copied()
+        self.0.get(&amount).copied()
     }
 
     /// Iterate through the (`Amount`, `PublicKey`) entries in the Map
     #[inline]
-    pub fn iter(&self) -> impl Iterator<Item = (&String, &PublicKey)> {
+    pub fn iter(&self) -> impl Iterator<Item = (&Amount, &PublicKey)> {
         self.0.iter()
     }
 }
@@ -87,7 +91,7 @@ pub struct KeysResponse {
     pub keysets: Vec<KeySet>,
 }
 
-/// Mint keys
+/// Mint key pairs per amount
 #[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
 pub struct MintKeys(BTreeMap<Amount, MintKeyPair>);
 
diff --git a/crates/cdk/src/nuts/nut02.rs b/crates/cdk/src/nuts/nut02.rs
index fbe12ba7..f24ef057 100644
--- a/crates/cdk/src/nuts/nut02.rs
+++ b/crates/cdk/src/nuts/nut02.rs
@@ -197,9 +197,10 @@ impl From<&Keys> for Id {
             5 - prefix it with a keyset ID version byte
         */
 
-        let mut keys: Vec<(&String, &super::PublicKey)> = map.iter().collect();
+        let mut keys: Vec<(&Amount, &super::PublicKey)> = map.iter()
+            .collect();
 
-        keys.sort_by_key(|(k, _v)| u64::from_str(k).unwrap());
+        keys.sort_by_key(|(&amt, _v)| u64::from(amt));
 
         let pubkeys_concat: Vec<u8> = keys
             .iter()