diff --git a/Cargo.toml b/Cargo.toml
index 3fdb6e2..b71e100 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -13,12 +13,12 @@ required-features = ["vpicc"]
 
 [dependencies]
 apdu-app = { version = "0.1", optional = true }
-cbor-smol = { version = "0.5", features = ["heapless-bytes-v0-3"] }
+cbor-smol = { version = "0.5", features = ["heapless-bytes-v0-5"] }
 delog = { version = "0.1.5", optional = true }
-flexiber = { version = "0.1", features = ["derive", "heapless"] }
-heapless = "0.7"
+flexiber = { version = "0.2", features = ["derive", "heapless"] }
+heapless = "0.9.1"
 hex-literal = "0.3"
-iso7816 = "0.1.3"
+iso7816 = "0.2.0"
 serde = { version = "1", default-features = false, features = ["derive"] }
 trussed = { version = "0.1", default-features = false, features = ["aes256-cbc", "chacha8-poly1305", "crypto-client", "ed255", "filesystem-client", "p256", "p384", "shared-secret", "serde-extensions", "tdes", "x255"], optional = true }
 trussed-auth = "0.4"
@@ -26,7 +26,7 @@ trussed-auth-backend = { version = "0.1.0", optional = true }
 untrusted = "0.9"
 vpicc = { version = "0.1.0", optional = true }
 log = "0.4"
-heapless-bytes = "0.3.0"
+heapless-bytes = "0.5.0"
 subtle = { version = "2", default-features = false }
 # TODO: only enable rsa features when needed
 trussed-core = { version = "0.1.0-rc.1", features = ["aes256-cbc", "chacha8-poly1305", "crypto-client", "ed255", "filesystem-client", "p256", "p384", "rsa2048", "rsa3072", "rsa4096", "shared-secret", "tdes", "x255"] }
diff --git a/src/dispatch.rs b/src/dispatch.rs
index b8bd0b0..eab8230 100644
--- a/src/dispatch.rs
+++ b/src/dispatch.rs
@@ -1,10 +1,11 @@
 use crate::{reply::Reply, Authenticator, /*constants::PIV_AID,*/ Result};
 
-use apdu_app::{App, CommandView, Data};
+use apdu_app::{App, CommandView};
+use heapless::VecView;
 use iso7816::{Interface, Status};
 
 #[cfg(feature = "apdu-dispatch")]
-impl<T, const R: usize> App<R> for Authenticator<T>
+impl<T> App for Authenticator<T>
 where
     T: crate::Client,
 {
@@ -12,7 +13,7 @@ where
         &mut self,
         interface: Interface,
         _apdu: CommandView<'_>,
-        reply: &mut Data<R>,
+        reply: &mut VecView<u8>,
     ) -> Result {
         if interface != Interface::Contact {
             return Err(Status::ConditionsOfUseNotSatisfied);
@@ -24,7 +25,12 @@ where
         self.deselect()
     }
 
-    fn call(&mut self, interface: Interface, apdu: CommandView<'_>, reply: &mut Data<R>) -> Result {
+    fn call(
+        &mut self,
+        interface: Interface,
+        apdu: CommandView<'_>,
+        reply: &mut VecView<u8>,
+    ) -> Result {
         if interface != Interface::Contact {
             return Err(Status::ConditionsOfUseNotSatisfied);
         }
diff --git a/src/lib.rs b/src/lib.rs
index 83331aa..7e7b65f 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -21,6 +21,7 @@ mod reply;
 pub mod state;
 mod tlv;
 
+use heapless::VecView;
 pub use piv_types::{AsymmetricAlgorithms, Pin, Puk};
 use trussed_chunked::ChunkedClient;
 use trussed_hpke::HpkeClient;
@@ -35,7 +36,7 @@ use core::convert::TryInto;
 
 use flexiber::EncodableHeapless;
 use heapless_bytes::Bytes;
-use iso7816::{Data, Status};
+use iso7816::Status;
 use trussed_auth::AuthClient;
 use trussed_core::mechanisms::Tdes;
 use trussed_core::types::{KeySerialization, Location, Mechanism, PathBuf, StorageAttributes};
@@ -136,7 +137,7 @@ where
     // The way apdu-dispatch currently works, this would deselect, resetting security indicators.
     pub fn deselect(&mut self) {}
 
-    pub fn select<const R: usize>(&mut self, mut reply: Reply<'_, R>) -> Result {
+    pub fn select(&mut self, mut reply: Reply<'_>) -> Result {
         use piv_types::Algorithms::*;
         info!("selecting PIV maybe");
 
@@ -154,10 +155,10 @@ where
         Ok(())
     }
 
-    pub fn respond<const R: usize>(
+    pub fn respond(
         &mut self,
         command: iso7816::command::CommandView<'_>,
-        reply: &mut Data<R>,
+        reply: &mut VecView<u8>,
     ) -> Result {
         let just_verified = self.state.volatile.app_security_status.pin_just_verified;
         self.state.volatile.app_security_status.pin_just_verified = false;
@@ -192,11 +193,11 @@ where
         }
     }
 
-    pub fn yubico_piv_extension<const R: usize>(
+    pub fn yubico_piv_extension(
         &mut self,
         data: &[u8],
         instruction: YubicoPivExtension,
-        mut reply: Reply<'_, R>,
+        mut reply: Reply<'_>,
     ) -> Result {
         info!("yubico extension: {:?}", &instruction);
         match instruction {
@@ -256,11 +257,11 @@ where
 }
 
 impl<T: Client> LoadedAuthenticator<'_, T> {
-    pub fn yubico_set_administration_key<const R: usize>(
+    pub fn yubico_set_administration_key(
         &mut self,
         data: &[u8],
         _touch_policy: TouchPolicy,
-        _reply: Reply<'_, R>,
+        _reply: Reply<'_>,
     ) -> Result {
         // cmd := apdu{
         //     instruction: insSetMGMKey,
@@ -424,12 +425,12 @@ impl<T: Client> LoadedAuthenticator<'_, T> {
     // - 9000, 61XX for success
     // - 6982 security status
     // - 6A80, 6A86 for data, P1/P2 issue
-    pub fn general_authenticate<const R: usize>(
+    pub fn general_authenticate(
         &mut self,
         auth: GeneralAuthenticate,
         data: &[u8],
         just_verified: bool,
-        mut reply: Reply<'_, R>,
+        mut reply: Reply<'_>,
     ) -> Result {
         // For "SSH", we need implement A.4.2 in SP-800-73-4 Part 2, ECDSA signatures
         //
@@ -562,11 +563,7 @@ impl<T: Client> LoadedAuthenticator<'_, T> {
         Ok(self.state.persistent.keys.administration)
     }
 
-    fn single_auth_1<const R: usize>(
-        &mut self,
-        auth: GeneralAuthenticate,
-        mut reply: Reply<'_, R>,
-    ) -> Result {
+    fn single_auth_1(&mut self, auth: GeneralAuthenticate, mut reply: Reply<'_>) -> Result {
         info!("Single auth 1");
         let key = self.validate_auth_management(auth)?;
         let plaintext = syscall!(self.trussed.random_bytes(key.alg.challenge_length())).bytes;
@@ -576,7 +573,7 @@ impl<T: Client> LoadedAuthenticator<'_, T> {
                 .encrypt(key.alg.mechanism(), key.id, &plaintext, &[], None))
             .ciphertext;
         self.state.volatile.command_cache = Some(CommandCache::SingleAuthChallengeReference(
-            Bytes::from_slice(&ciphertext).unwrap(),
+            Bytes::try_from(&*ciphertext).unwrap(),
         ));
 
         reply.expand(&[0x7C])?;
@@ -619,11 +616,7 @@ impl<T: Client> LoadedAuthenticator<'_, T> {
         Ok(())
     }
 
-    fn mutual_auth_1<const R: usize>(
-        &mut self,
-        auth: GeneralAuthenticate,
-        mut reply: Reply<'_, R>,
-    ) -> Result {
+    fn mutual_auth_1(&mut self, auth: GeneralAuthenticate, mut reply: Reply<'_>) -> Result {
         info!("Mutual auth 1");
         let key = self.validate_auth_management(auth)?;
         let plaintext = syscall!(self.trussed.random_bytes(key.alg.challenge_length())).bytes;
@@ -635,7 +628,7 @@ impl<T: Client> LoadedAuthenticator<'_, T> {
             .ciphertext;
 
         self.state.volatile.command_cache = Some(CommandCache::MutualAuthWitnessReference(
-            Bytes::from_slice(&plaintext).unwrap(),
+            Bytes::try_from(&*plaintext).unwrap(),
         ));
 
         reply.expand(&[0x7C])?;
@@ -649,12 +642,12 @@ impl<T: Client> LoadedAuthenticator<'_, T> {
         Ok(())
     }
 
-    fn mutual_auth_2<const R: usize>(
+    fn mutual_auth_2(
         &mut self,
         auth: GeneralAuthenticate,
         response: &[u8],
         challenge: &[u8],
-        mut reply: Reply<'_, R>,
+        mut reply: Reply<'_>,
     ) -> Result {
         use subtle::ConstantTimeEq;
 
@@ -703,12 +696,12 @@ impl<T: Client> LoadedAuthenticator<'_, T> {
     }
 
     // Sign a message. For RSA, since the key is exposed as a raw key, so it can also be used for decryption
-    fn sign<const R: usize>(
+    fn sign(
         &mut self,
         auth: GeneralAuthenticate,
         message: &[u8],
         just_verified: bool,
-        mut reply: Reply<'_, R>,
+        mut reply: Reply<'_>,
     ) -> Result {
         debug!("Request for sign, data length: {}, data:", message.len());
         // error!("{}", delog::hexstr!(message));
@@ -754,11 +747,11 @@ impl<T: Client> LoadedAuthenticator<'_, T> {
         )
     }
 
-    fn key_agreement<const R: usize>(
+    fn key_agreement(
         &mut self,
         auth: GeneralAuthenticate,
         data: &[u8],
-        mut reply: Reply<'_, R>,
+        mut reply: Reply<'_>,
         just_verified: bool,
     ) -> Result {
         info!("Request for exponentiation");
@@ -839,11 +832,11 @@ impl<T: Client> LoadedAuthenticator<'_, T> {
         )
     }
 
-    pub fn generate_asymmetric_keypair<const R: usize>(
+    pub fn generate_asymmetric_keypair(
         &mut self,
         reference: GenerateKeyReference,
         data: &[u8],
-        mut reply: Reply<'_, R>,
+        mut reply: Reply<'_>,
     ) -> Result {
         if !self
             .state
@@ -967,11 +960,7 @@ impl<T: Client> LoadedAuthenticator<'_, T> {
         Ok(())
     }
 
-    fn get_data<const R: usize>(
-        &mut self,
-        container: Container,
-        mut reply: Reply<'_, R>,
-    ) -> Result {
+    fn get_data(&mut self, container: Container, mut reply: Reply<'_>) -> Result {
         let read_valid =
             self.state
                 .volatile
@@ -1045,7 +1034,7 @@ impl<T: Client> LoadedAuthenticator<'_, T> {
         Ok(())
     }
 
-    fn get_key_history_object<const R: usize>(&mut self, mut reply: Reply<'_, R>) -> Result {
+    fn get_key_history_object(&mut self, mut reply: Reply<'_>) -> Result {
         use state::ContainerStorage;
 
         let mut num_certs = 0;
@@ -1063,12 +1052,12 @@ impl<T: Client> LoadedAuthenticator<'_, T> {
         Ok(())
     }
 
-    fn import_asymmetric_key<const R: usize>(
+    fn import_asymmetric_key(
         &mut self,
         algo: AsymmetricAlgorithms,
         key: AsymmetricKeyReference,
         #[cfg_attr(not(feature = "rsa"), allow(unused))] data: &[u8],
-        mut _reply: Reply<'_, R>,
+        mut _reply: Reply<'_>,
     ) -> Result {
         if !self
             .state
diff --git a/src/reply.rs b/src/reply.rs
index ebca2a3..33509d8 100644
--- a/src/reply.rs
+++ b/src/reply.rs
@@ -3,22 +3,22 @@ use iso7816::Status;
 use core::ops::{Deref, DerefMut};
 
 #[derive(Debug)]
-pub struct Reply<'v, const R: usize>(pub &'v mut heapless::Vec<u8, R>);
+pub struct Reply<'v>(pub &'v mut heapless::VecView<u8>);
 
-impl<'v, const R: usize> Deref for Reply<'v, R> {
-    type Target = &'v mut heapless::Vec<u8, R>;
+impl<'v> Deref for Reply<'v> {
+    type Target = &'v mut heapless::VecView<u8>;
     fn deref(&self) -> &Self::Target {
         &self.0
     }
 }
 
-impl<const R: usize> DerefMut for Reply<'_, R> {
+impl DerefMut for Reply<'_> {
     fn deref_mut(&mut self) -> &mut Self::Target {
         &mut self.0
     }
 }
 
-impl<const R: usize> Reply<'_, R> {
+impl Reply<'_> {
     /// Extend the reply and return an error otherwise
     /// The MoreAvailable and GET RESPONSE mechanisms are handled by adpu_dispatch
     ///
@@ -82,7 +82,7 @@ impl<const R: usize> Reply<'_, R> {
         })
     }
 
-    pub fn lend(&mut self) -> Reply<'_, R> {
+    pub fn lend(&mut self) -> Reply<'_> {
         Reply(self.0)
     }
 }
diff --git a/src/state.rs b/src/state.rs
index d7567b2..4a24146 100644
--- a/src/state.rs
+++ b/src/state.rs
@@ -200,8 +200,8 @@ impl Keys {
                     storage,
                     user_public_key,
                     new.id,
-                    Bytes::from_slice(key.name().as_str().as_bytes()).unwrap(),
-                    Bytes::from_slice(HPKE_SEALKEY_REFERENCE_INFO).unwrap(),
+                    Bytes::try_from(key.name().as_str().as_bytes()).unwrap(),
+                    Bytes::try_from(HPKE_SEALKEY_REFERENCE_INFO).unwrap(),
                 ));
 
                 KeyOrEncryptedWithAlg::Encrypted(match key {
@@ -382,8 +382,8 @@ impl LoadedState<'_> {
             key.name().into(),
             options.storage,
             Location::Volatile,
-            Bytes::from_slice(key.name().as_str().as_bytes()).unwrap(),
-            Bytes::from_slice(HPKE_SEALKEY_REFERENCE_INFO).unwrap(),
+            Bytes::try_from(key.name().as_str().as_bytes()).unwrap(),
+            Bytes::try_from(HPKE_SEALKEY_REFERENCE_INFO).unwrap(),
         ))
         .map_err(|_err| {
             error!("Failed to unseal key: {_err:?}");
@@ -460,7 +460,7 @@ impl Volatile {
         client: &mut T,
     ) -> &'this mut PinVerified {
         self.clear_pin_verified(client);
-        let pin = Bytes::from_slice(&value.0).expect("Convertion of static array");
+        let pin = Bytes::try_from(&value.0).expect("Convertion of static array");
         let syscall_res = try_syscall!(client.get_pin_key(PinType::UserPin, pin));
         let pin_key = match syscall_res {
             Err(_err) => {
@@ -532,8 +532,8 @@ impl Volatile {
             data_encryption_sealed_key_path,
             options.storage,
             Location::Volatile,
-            Bytes::from_slice(ContainerStorage(container).path_key_str().as_bytes()).unwrap(),
-            Bytes::from_slice(HPKE_SEALKEY_CONTAINER_INFO).unwrap(),
+            Bytes::try_from(ContainerStorage(container).path_key_str().as_bytes()).unwrap(),
+            Bytes::try_from(HPKE_SEALKEY_CONTAINER_INFO).unwrap(),
         )) else {
             return Ok(ReadValid::EncryptedNotFound);
         };
@@ -680,7 +680,7 @@ impl Persistent {
         value: &Puk,
         client: &mut T,
     ) -> Result<Option<KeyId>, Status> {
-        let puk = Bytes::from_slice(&value.0).expect("Convertion of static array");
+        let puk = Bytes::try_from(&value.0).expect("Convertion of static array");
         try_syscall!(client.get_pin_key(PinType::Puk, puk))
             .map(|r| r.result)
             .map_err(|_err| {
@@ -695,8 +695,8 @@ impl Persistent {
         new_value: &Pin,
         client: &mut T,
     ) -> bool {
-        let old_pin = Bytes::from_slice(&old_value.0).expect("Convertion of static array");
-        let new_pin = Bytes::from_slice(&new_value.0).expect("Convertion of static array");
+        let old_pin = Bytes::try_from(&old_value.0).expect("Convertion of static array");
+        let new_pin = Bytes::try_from(&new_value.0).expect("Convertion of static array");
         try_syscall!(client.change_pin(PinType::UserPin, old_pin, new_pin))
             .map(|r| r.success)
             .unwrap_or(false)
@@ -708,8 +708,8 @@ impl Persistent {
         new_value: &Puk,
         client: &mut T,
     ) -> bool {
-        let old_puk = Bytes::from_slice(&old_value.0).expect("Convertion of static array");
-        let new_puk = Bytes::from_slice(&new_value.0).expect("Convertion of static array");
+        let old_puk = Bytes::try_from(&old_value.0).expect("Convertion of static array");
+        let new_puk = Bytes::try_from(&new_value.0).expect("Convertion of static array");
         try_syscall!(client.change_pin(PinType::Puk, old_puk, new_puk))
             .map(|r| r.success)
             .unwrap_or(false)
@@ -721,7 +721,7 @@ impl Persistent {
         old_key: KeyId,
         client: &mut T,
     ) -> Result<(), Status> {
-        let new_pin = Bytes::from_slice(&new_pin.0).expect("Convertion of static array");
+        let new_pin = Bytes::try_from(&new_pin.0).expect("Convertion of static array");
         try_syscall!(client.set_pin_with_key(
             PinType::UserPin,
             new_pin,
@@ -740,7 +740,7 @@ impl Persistent {
         new_puk: Puk,
         client: &mut T,
     ) -> Result<(), Status> {
-        let new_puk = Bytes::from_slice(&new_puk.0).expect("Convertion of static array");
+        let new_puk = Bytes::try_from(&new_puk.0).expect("Convertion of static array");
         try_syscall!(client.set_pin(PinType::Puk, new_puk, Some(Self::PUK_RETRIES_DEFAULT), true))
             .map_err(|_err| {
                 error!("Failed to set puk");
@@ -859,7 +859,7 @@ impl Persistent {
 
     fn init_pins<T: crate::Client>(client: &mut T, options: &crate::Options) -> Result<(), Status> {
         let default_pin =
-            Bytes::from_slice(&Self::DEFAULT_PIN.0).expect("Convertion of static array");
+            Bytes::try_from(&Self::DEFAULT_PIN.0).expect("Convertion of static array");
         try_syscall!(client.set_pin(
             PinType::UserPin,
             default_pin.clone(),
@@ -871,7 +871,7 @@ impl Persistent {
             Status::UnspecifiedPersistentExecutionError
         })?;
         let default_puk =
-            Bytes::from_slice(&Self::DEFAULT_PUK.0).expect("Convertion of static array");
+            Bytes::try_from(&Self::DEFAULT_PUK.0).expect("Convertion of static array");
         try_syscall!(client.set_pin(
             PinType::Puk,
             default_puk.clone(),
@@ -933,7 +933,7 @@ impl Persistent {
         syscall!(client.write_file(
             options.storage,
             PathBuf::from(USER_PUBLIC_KEY),
-            Bytes::from_slice(&key).unwrap(),
+            Bytes::try_from(&*key).unwrap(),
             None
         ));
 
@@ -1068,11 +1068,11 @@ fn load_if_exists(
 }
 
 /// Returns false if the file does not exist
-fn load_if_exists_streaming<const R: usize>(
+fn load_if_exists_streaming(
     client: &mut impl crate::Client,
     location: Location,
     path: &PathBuf,
-    mut buffer: Reply<'_, R>,
+    mut buffer: Reply<'_>,
     encryption: Option<KeyId>,
 ) -> Result<bool, Status> {
     let offset = buffer.len();
@@ -1218,11 +1218,11 @@ impl ContainerStorage {
     }
 
     // Write the length of the file and write
-    pub fn load<const R: usize>(
+    pub fn load(
         self,
         client: &mut impl crate::Client,
         storage: Location,
-        mut reply: Reply<'_, R>,
+        mut reply: Reply<'_>,
         read_valid: ReadValid,
     ) -> Result<bool, Status> {
         let encryption = match read_valid {
@@ -1292,8 +1292,8 @@ impl ContainerStorage {
             storage,
             user_public_key,
             key_to_seal,
-            Bytes::from_slice(self.path_key_str().as_bytes()).unwrap(),
-            Bytes::from_slice(HPKE_SEALKEY_CONTAINER_INFO).unwrap(),
+            Bytes::try_from(self.path_key_str().as_bytes()).unwrap(),
+            Bytes::try_from(HPKE_SEALKEY_CONTAINER_INFO).unwrap(),
         ));
         syscall!(client.delete(user_public_key));