diff --git a/bindings/cashu-sdk-ffi/src/cashu_sdk.udl b/bindings/cashu-sdk-ffi/src/cashu_sdk.udl
index 69e62ba1..a4d77b93 100644
--- a/bindings/cashu-sdk-ffi/src/cashu_sdk.udl
+++ b/bindings/cashu-sdk-ffi/src/cashu_sdk.udl
@@ -26,6 +26,11 @@ interface Amount {
 };
 
 
+interface Secret {
+	constructor();
+	sequence<u8> as_bytes();	
+};
+
 interface PublicKey {
     [Throws=CashuError, Name=from_hex]
     constructor(string hex);
@@ -46,9 +51,9 @@ interface BlindedMessage {
 };
 
 interface Proof {
-	constructor(Amount amount, string secret, PublicKey c, string? id);
+	constructor(Amount amount, Secret secret, PublicKey c, string? id);
 	Amount amount();
-	string secret();
+	Secret secret();
 	PublicKey c();
 	string? id();
 };
@@ -61,9 +66,9 @@ interface BlindedSignature {
 };
 
 interface MintProof {
-	constructor(Amount? amount, string secret, PublicKey? c, string? id);
+	constructor(Amount? amount, Secret secret, PublicKey? c, string? id);
 	Amount? amount();
-	string secret();
+	Secret secret();
 	PublicKey? c();
 	string? id();
 	
@@ -94,7 +99,7 @@ interface BlindedMessages {
     [Throws=CashuError, Name=blank]
 	constructor(Amount fee_reserve);
 	sequence<BlindedMessage> blinded_messages();
-	sequence<string> secrets();
+	sequence<Secret> secrets();
 	sequence<SecretKey> rs();
 	sequence<Amount> amounts();
 };
@@ -314,7 +319,7 @@ interface Wallet {
 
 
 interface Mint {
-	constructor(string secret, string derivation_path, record<string, MintKeySet> inactive_keysets, sequence<string> spent_secrets, u8 max_order);
+	constructor(string secret, string derivation_path, record<string, MintKeySet> inactive_keysets, sequence<Secret> spent_secrets, u8 max_order);
 	KeySet active_keyset_pubkeys();
 	KeySetResponse keysets();
 	MintKeySet active_keyset();
@@ -324,7 +329,7 @@ interface Mint {
     [Throws=CashuSdkError]
 	SplitResponse proccess_split_request(SplitRequest split_request);
     [Throws=CashuSdkError]
-	string verify_proof(Proof proof);
+	void verify_proof(Proof proof);
     [Throws=CashuSdkError]
 	void verify_melt_request(MeltRequest melt_request);
     [Throws=CashuSdkError]
diff --git a/bindings/cashu-sdk-ffi/src/lib.rs b/bindings/cashu-sdk-ffi/src/lib.rs
index db0bf806..0692df2d 100644
--- a/bindings/cashu-sdk-ffi/src/lib.rs
+++ b/bindings/cashu-sdk-ffi/src/lib.rs
@@ -10,8 +10,8 @@ mod ffi {
         CheckFeesRequest, CheckFeesResponse, CheckSpendableRequest, CheckSpendableResponse,
         InvoiceStatus, KeyPair, KeySet, KeySetResponse, Keys, MeltRequest, MeltResponse, MintInfo,
         MintKeySet, MintProof, MintProofs, MintRequest, MintVersion, Nut05MeltRequest,
-        Nut05MeltResponse, PostMintResponse, Proof, PublicKey, RequestMintResponse, SecretKey,
-        SplitRequest, SplitResponse, Token,
+        Nut05MeltResponse, PostMintResponse, Proof, PublicKey, RequestMintResponse, Secret,
+        SecretKey, SplitRequest, SplitResponse, Token,
     };
 
     pub use crate::client::Client;
diff --git a/bindings/cashu-sdk-ffi/src/mint.rs b/bindings/cashu-sdk-ffi/src/mint.rs
index 0e75b295..0f13b2e7 100644
--- a/bindings/cashu-sdk-ffi/src/mint.rs
+++ b/bindings/cashu-sdk-ffi/src/mint.rs
@@ -9,7 +9,8 @@ use cashu_sdk::mint::Mint as MintSdk;
 use crate::error::Result;
 use cashu_ffi::{
     Amount, CheckSpendableRequest, CheckSpendableResponse, KeySet, KeySetResponse, MeltRequest,
-    MeltResponse, MintKeySet, MintRequest, PostMintResponse, Proof, SplitRequest, SplitResponse,
+    MeltResponse, MintKeySet, MintRequest, PostMintResponse, Proof, Secret, SplitRequest,
+    SplitResponse,
 };
 
 pub struct Mint {
@@ -21,10 +22,13 @@ impl Mint {
         secret: String,
         derivation_path: String,
         inactive_keysets: HashMap<String, Arc<MintKeySet>>,
-        spent_secrets: Vec<String>,
+        spent_secrets: Vec<Arc<Secret>>,
         max_order: u8,
     ) -> Self {
-        let spent_secrets = spent_secrets.into_iter().collect();
+        let spent_secrets = spent_secrets
+            .into_iter()
+            .map(|s| s.as_ref().deref().clone())
+            .collect();
 
         let inactive_keysets = inactive_keysets
             .into_iter()
@@ -89,7 +93,7 @@ impl Mint {
         ))
     }
 
-    pub fn verify_proof(&self, proof: Arc<Proof>) -> Result<String> {
+    pub fn verify_proof(&self, proof: Arc<Proof>) -> Result<()> {
         Ok(self
             .inner
             .read()
diff --git a/crates/cashu-sdk/src/mint.rs b/crates/cashu-sdk/src/mint.rs
index 8eecf028..41bef547 100644
--- a/crates/cashu-sdk/src/mint.rs
+++ b/crates/cashu-sdk/src/mint.rs
@@ -14,14 +14,15 @@ use cashu::nuts::nut07::CheckSpendableResponse;
 use cashu::nuts::nut08::MeltRequest;
 use cashu::nuts::nut08::MeltResponse;
 use cashu::nuts::*;
+use cashu::secret::Secret;
 use cashu::Amount;
 
 pub struct Mint {
     //    pub pubkey: PublicKey,
     pub active_keyset: nut02::mint::KeySet,
     pub inactive_keysets: HashMap<String, nut02::mint::KeySet>,
-    pub spent_secrets: HashSet<String>,
-    pub pending_secrets: HashSet<String>,
+    pub spent_secrets: HashSet<Secret>,
+    pub pending_secrets: HashSet<Secret>,
 }
 
 impl Mint {
@@ -29,7 +30,7 @@ impl Mint {
         secret: &str,
         derivation_path: &str,
         inactive_keysets: HashMap<String, nut02::mint::KeySet>,
-        spent_secrets: HashSet<String>,
+        spent_secrets: HashSet<Secret>,
         max_order: u8,
     ) -> Self {
         Self {
@@ -126,7 +127,7 @@ impl Mint {
 
         let proof_count = split_request.proofs.len();
 
-        let secrets: HashSet<String> = split_request.proofs.into_iter().map(|p| p.secret).collect();
+        let secrets: HashSet<Secret> = split_request.proofs.into_iter().map(|p| p.secret).collect();
 
         // Check that there are no duplicate proofs in request
         if secrets.len().ne(&proof_count) {
@@ -190,7 +191,7 @@ impl Mint {
         };
 
         verify_message(
-            keypair.secret_key.to_owned().into(),
+            keypair.secret_key.clone().into(),
             proof.c.clone().into(),
             &proof.secret,
         )?;
@@ -225,11 +226,7 @@ impl Mint {
             return Err(Error::Amount);
         }
 
-        let secrets: HashSet<&str> = melt_request
-            .proofs
-            .iter()
-            .map(|p| p.secret.as_str())
-            .collect();
+        let secrets: HashSet<&Secret> = melt_request.proofs.iter().map(|p| &p.secret).collect();
 
         // Ensure proofs are unique and not being double spent
         if melt_request.proofs.len().ne(&secrets.len()) {
diff --git a/crates/cashu/src/dhke.rs b/crates/cashu/src/dhke.rs
index cb1625ab..2f87f0c0 100644
--- a/crates/cashu/src/dhke.rs
+++ b/crates/cashu/src/dhke.rs
@@ -128,7 +128,7 @@ pub fn sign_message(
 pub fn verify_message(
     a: SecretKey,
     unblinded_message: k256::PublicKey,
-    msg: Secret,
+    msg: &Secret,
 ) -> Result<(), error::mint::Error> {
     // Y
     let y = hash_to_curve(msg.as_bytes());
@@ -273,6 +273,6 @@ mod tests {
         // C
         let c = unblind_message(signed.into(), blinded.1, bob_pub.into()).unwrap();
 
-        assert!(verify_message(bob_sec, c.into(), x).is_ok());
+        assert!(verify_message(bob_sec, c.into(), &x).is_ok());
     }
 }