diff --git a/Cargo.toml b/Cargo.toml
index 24e7d0c..41178c4 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -22,7 +22,7 @@ std = ["curve25519-dalek/std", "getrandom", "rand/std", "rand/std_rng", "num-big
 serialize = ["serde", "base64", "generic-array/serde", "curve25519-dalek/serde"]
 
 [dependencies]
-argon2 = { version = "0.2", default-features = false, optional = true }
+argon2 = { version = "0.3", default-features = false, features = ["alloc"], optional = true }
 base64 = { version = "0.13", default-features = false, features = ["alloc"], optional = true }
 constant_time_eq = "0.1"
 curve25519-dalek = { version = "3", default-features = false }
diff --git a/src/group/x25519.rs b/src/group/x25519.rs
index a48c740..228c223 100644
--- a/src/group/x25519.rs
+++ b/src/group/x25519.rs
@@ -127,7 +127,7 @@ fn test() -> Result<(), ProtocolError> {
     } = client.finish(
         &mut OsRng,
         message,
-        ClientRegistrationFinishParameters::Default,
+        ClientRegistrationFinishParameters::default(),
     )?;
     let server_registration = ServerRegistration::finish(message);
 
@@ -152,7 +152,7 @@ fn test() -> Result<(), ProtocolError> {
         session_key: client_session_key,
         export_key: login_export_key,
         ..
-    } = client.finish(message, ClientLoginFinishParameters::Default)?;
+    } = client.finish(message, ClientLoginFinishParameters::default())?;
     let server_session_key = server.finish(message)?.session_key;
 
     assert_eq!(register_export_key, login_export_key);
@@ -172,7 +172,7 @@ fn test() -> Result<(), ProtocolError> {
     )?;
 
     assert!(matches!(
-        client.finish(message, ClientLoginFinishParameters::Default),
+        client.finish(message, ClientLoginFinishParameters::default()),
         Err(ProtocolError::InvalidLoginError)
     ));
 
diff --git a/src/keypair.rs b/src/keypair.rs
index 4d6f2a2..caf4b72 100644
--- a/src/keypair.rs
+++ b/src/keypair.rs
@@ -507,7 +507,7 @@ mod tests {
             .finish(
                 &mut OsRng,
                 message,
-                ClientRegistrationFinishParameters::Default,
+                ClientRegistrationFinishParameters::default(),
             )
             .unwrap();
         let file = ServerRegistration::finish(message);
@@ -530,7 +530,7 @@ mod tests {
         )
         .unwrap();
         let ClientLoginFinishResult { message, .. } = client
-            .finish(message, ClientLoginFinishParameters::Default)
+            .finish(message, ClientLoginFinishParameters::default())
             .unwrap();
         server.finish(message).unwrap();
     }
diff --git a/src/lib.rs b/src/lib.rs
index d6e5d6a..65f4ceb 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -578,7 +578,7 @@
 //!
 //! But, for applications that wish to cryptographically bind these identities to
 //! the registered password file as well as the session key output by the login phase, these custom identifiers can be specified through
-//! [ClientRegistrationFinishParameters::WithIdentifiers] in [Client Registration Finish](#client-registration-finish):
+//! [ClientRegistrationFinishParameters] in [Client Registration Finish](#client-registration-finish):
 //! ```
 //! # use opaque_ke::{
 //! #   errors::ProtocolError,
@@ -606,11 +606,12 @@
 //! let client_registration_finish_result = client_registration_start_result.state.finish(
 //!     &mut client_rng,
 //!     server_registration_start_result.message,
-//!     ClientRegistrationFinishParameters::WithIdentifiers(
-//!         Identifiers::ClientAndServerIdentifiers(
+//!     ClientRegistrationFinishParameters::new(
+//!         Some(Identifiers::ClientAndServerIdentifiers(
 //!             b"Alice_the_Cryptographer".to_vec(),
 //!             b"Facebook".to_vec(),
-//!         ),
+//!         )),
+//!         None,
 //!     ),
 //! )?;
 //! # Ok::<(), ProtocolError>(())
@@ -641,7 +642,7 @@
 //! # let mut server_rng = OsRng;
 //! # let server_setup = ServerSetup::<Default>::new(&mut server_rng);
 //! # let server_registration_start_result = ServerRegistration::<Default>::start(&server_setup, client_registration_start_result.message, b"alice@example.com")?;
-//! # let client_registration_finish_result = client_registration_start_result.state.finish(&mut client_rng, server_registration_start_result.message, ClientRegistrationFinishParameters::WithIdentifiers(Identifiers::ClientAndServerIdentifiers(b"Alice_the_Cryptographer".to_vec(), b"Facebook".to_vec())))?;
+//! # let client_registration_finish_result = client_registration_start_result.state.finish(&mut client_rng, server_registration_start_result.message, ClientRegistrationFinishParameters::new(Some(Identifiers::ClientAndServerIdentifiers(b"Alice_the_Cryptographer".to_vec(), b"Facebook".to_vec())), None))?;
 //! # let password_file_bytes = ServerRegistration::<Default>::finish(client_registration_finish_result.message).serialize();
 //! # let client_login_start_result = ClientLogin::<Default>::start(
 //! #   &mut client_rng,
@@ -666,7 +667,7 @@
 //! # Ok::<(), ProtocolError>(())
 //! ```
 //!
-//! as well as [ClientLoginFinishParameters::WithIdentifiers] in [Client Login Finish](#client-login-finish):
+//! as well as [ClientLoginFinishParameters] in [Client Login Finish](#client-login-finish):
 //! ```
 //! # use opaque_ke::{
 //! #   errors::ProtocolError,
@@ -691,7 +692,7 @@
 //! # let mut server_rng = OsRng;
 //! # let server_setup = ServerSetup::<Default>::new(&mut server_rng);
 //! # let server_registration_start_result = ServerRegistration::<Default>::start(&server_setup, client_registration_start_result.message, b"alice@example.com")?;
-//! # let client_registration_finish_result = client_registration_start_result.state.finish(&mut client_rng, server_registration_start_result.message, ClientRegistrationFinishParameters::WithIdentifiers(Identifiers::ClientAndServerIdentifiers(b"Alice_the_Cryptographer".to_vec(), b"Facebook".to_vec())))?;
+//! # let client_registration_finish_result = client_registration_start_result.state.finish(&mut client_rng, server_registration_start_result.message, ClientRegistrationFinishParameters::new(Some(Identifiers::ClientAndServerIdentifiers(b"Alice_the_Cryptographer".to_vec(), b"Facebook".to_vec())), None))?;
 //! # let password_file_bytes = ServerRegistration::<Default>::finish(client_registration_finish_result.message).serialize();
 //! # let client_login_start_result = ClientLogin::<Default>::start(
 //! #     &mut client_rng,
@@ -705,11 +706,13 @@
 //! #     ServerLogin::start(&mut server_rng, &server_setup, Some(password_file), client_login_start_result.message, b"alice@example.com", ServerLoginStartParameters::WithIdentifiers(Identifiers::ClientAndServerIdentifiers(b"Alice_the_Cryptographer".to_vec(), b"Facebook".to_vec())))?;
 //! let client_login_finish_result = client_login_start_result.state.finish(
 //!     server_login_start_result.message,
-//!     ClientLoginFinishParameters::WithIdentifiers(
-//!         Identifiers::ClientAndServerIdentifiers(
+//!     ClientLoginFinishParameters::new(
+//!         None,
+//!         Some(Identifiers::ClientAndServerIdentifiers(
 //!             b"Alice_the_Cryptographer".to_vec(),
 //!             b"Facebook".to_vec(),
-//!         ),
+//!         )),
+//!         None,
 //!     ),
 //! )?;
 //!
@@ -727,7 +730,7 @@
 //! so as to bind the integrity of application-specific data or configuration parameters to the security of the key exchange.
 //! During the login phase, the client and server can specify this context using:
 //! - The second login message, where the server can populate [ServerLoginStartParameters::WithContext], and
-//! - The third login message, where the client can populate [ClientLoginFinishParameters::WithContext].
+//! - The third login message, where the client can populate [ClientLoginFinishParameters].
 //!
 //! For both of these messages, the `WithContextAndIdentifiers` variant can be used to specify these fields in addition to
 //! [custom identifiers](#custom-identifiers), with the ordering of the fields as
@@ -780,7 +783,8 @@
 //!     fn public_key(
 //!         &self
 //!     ) -> Result<PublicKey<RistrettoPoint>, InternalError<Self::Error>> {
-//!         YourRemoteKey::public_key(self).map(PublicKey::from_arr).map_err(InternalError::Custom)
+//!         YourRemoteKey::public_key(self).map(PublicKey::from_arr)
+//!             .map_err(InternalError::Custom)
 //!     }
 //!
 //!     fn serialize(&self) -> Vec<u8> {
diff --git a/src/opaque.rs b/src/opaque.rs
index b784bbe..1591f6c 100644
--- a/src/opaque.rs
+++ b/src/opaque.rs
@@ -222,16 +222,29 @@ pub(crate) fn bytestrings_from_identifiers(
 
 /// Optional parameters for client registration finish
 #[derive(Clone)]
-pub enum ClientRegistrationFinishParameters {
+pub struct ClientRegistrationFinishParameters<'h, CS: CipherSuite> {
     /// Specifying the identifiers idU and idS
-    WithIdentifiers(Identifiers),
-    /// No identifiers or private key specified
-    Default,
+    pub identifiers: Option<Identifiers>,
+    /// Specifying a configuration for the slow hash
+    pub slow_hash: Option<&'h CS::SlowHash>,
 }
 
-impl Default for ClientRegistrationFinishParameters {
+impl<'h, CS: CipherSuite> Default for ClientRegistrationFinishParameters<'h, CS> {
     fn default() -> Self {
-        Self::Default
+        Self {
+            identifiers: None,
+            slow_hash: None,
+        }
+    }
+}
+
+impl<'h, CS: CipherSuite> ClientRegistrationFinishParameters<'h, CS> {
+    /// Create a new [`ClientRegistrationFinishParameters`]
+    pub fn new(identifiers: Option<Identifiers>, slow_hash: Option<&'h CS::SlowHash>) -> Self {
+        Self {
+            identifiers,
+            slow_hash,
+        }
     }
 }
 
@@ -312,22 +325,15 @@ impl<CS: CipherSuite> ClientRegistration<CS> {
         self,
         rng: &mut R,
         r2: RegistrationResponse<CS>,
-        params: ClientRegistrationFinishParameters,
+        params: ClientRegistrationFinishParameters<CS>,
     ) -> Result<ClientRegistrationFinishResult<CS>, ProtocolError> {
-        let optional_ids = match params {
-            ClientRegistrationFinishParameters::WithIdentifiers(ids) => Some(ids),
-            ClientRegistrationFinishParameters::Default => None,
-        };
-
         // Check for reflected value from server and halt if detected
         if self.alpha.ct_equal(&r2.beta) {
             return Err(ProtocolError::ReflectedValueError);
         }
 
-        let password_derived_key = get_password_derived_key::<CS::OprfGroup, CS::SlowHash, CS::Hash>(
-            &self.token,
-            r2.beta,
-        )?;
+        let password_derived_key =
+            get_password_derived_key::<CS>(&self.token, r2.beta, params.slow_hash)?;
 
         #[cfg_attr(not(test), allow(unused_variables))]
         let (randomized_pwd, h) = Hkdf::<CS::Hash>::extract(None, &password_derived_key);
@@ -335,8 +341,12 @@ impl<CS: CipherSuite> ClientRegistration<CS> {
         h.expand(STR_MASKING_KEY, &mut masking_key)
             .map_err(|_| InternalError::HkdfError)?;
 
-        let result =
-            Envelope::<CS>::seal(rng, &password_derived_key, &r2.server_s_pk, optional_ids)?;
+        let result = Envelope::<CS>::seal(
+            rng,
+            &password_derived_key,
+            &r2.server_s_pk,
+            params.identifiers,
+        )?;
 
         Ok(ClientRegistrationFinishResult {
             message: RegistrationUpload {
@@ -553,21 +563,37 @@ impl<CS: CipherSuite> Clone for ClientLoginStartResult<CS> {
 
 /// Optional parameters for client login finish
 #[derive(Clone)]
-pub enum ClientLoginFinishParameters {
+pub struct ClientLoginFinishParameters<'h, CS: CipherSuite> {
     /// Specifying a context field that the server must agree on
-    WithContext(Vec<u8>),
+    pub context: Option<Vec<u8>>,
     /// Specifying a user identifier and server identifier that will be matched against the server
-    WithIdentifiers(Identifiers),
-    /// Specifying a context field that the server must agree on,
-    /// along with a user identifier and server identifier and context that will be matched against the server
-    WithContextAndIdentifiers(Vec<u8>, Identifiers),
-    /// No custom identifiers and no context
-    Default,
+    pub identifiers: Option<Identifiers>,
+    /// Specifying a configuration for the slow hash
+    pub slow_hash: Option<&'h CS::SlowHash>,
 }
 
-impl Default for ClientLoginFinishParameters {
+impl<'h, CS: CipherSuite> Default for ClientLoginFinishParameters<'h, CS> {
     fn default() -> Self {
-        Self::Default
+        Self {
+            context: None,
+            identifiers: None,
+            slow_hash: None,
+        }
+    }
+}
+
+impl<'h, CS: CipherSuite> ClientLoginFinishParameters<'h, CS> {
+    /// Create a new [`ClientLoginFinishParameters`]
+    pub fn new(
+        context: Option<Vec<u8>>,
+        identifiers: Option<Identifiers>,
+        slow_hash: Option<&'h CS::SlowHash>,
+    ) -> Self {
+        Self {
+            context,
+            identifiers,
+            slow_hash,
+        }
     }
 }
 
@@ -638,18 +664,8 @@ impl<CS: CipherSuite> ClientLogin<CS> {
     pub fn finish(
         self,
         credential_response: CredentialResponse<CS>,
-        params: ClientLoginFinishParameters,
+        params: ClientLoginFinishParameters<CS>,
     ) -> Result<ClientLoginFinishResult<CS>, ProtocolError> {
-        let (context, optional_ids) = match params {
-            ClientLoginFinishParameters::Default => (vec![], None),
-            ClientLoginFinishParameters::WithContext(context) => (context, None),
-            ClientLoginFinishParameters::WithIdentifiers(ids) => (vec![], Some(ids)),
-            // add context
-            ClientLoginFinishParameters::WithContextAndIdentifiers(context, ids) => {
-                (context, Some(ids))
-            }
-        };
-
         // Check if beta value from server is equal to alpha value from client
         let credential_request =
             CredentialRequest::<CS>::deserialize(&self.serialized_credential_request[..])?;
@@ -657,9 +673,10 @@ impl<CS: CipherSuite> ClientLogin<CS> {
             return Err(ProtocolError::ReflectedValueError);
         }
 
-        let password_derived_key = get_password_derived_key::<CS::OprfGroup, CS::SlowHash, CS::Hash>(
+        let password_derived_key = get_password_derived_key::<CS>(
             &self.token,
             credential_response.beta,
+            params.slow_hash,
         )?;
 
         let h = Hkdf::<CS::Hash>::new(None, &password_derived_key);
@@ -679,7 +696,11 @@ impl<CS: CipherSuite> ClientLogin<CS> {
         let server_s_pk_bytes = server_s_pk.to_arr().to_vec();
 
         let opened_envelope = &envelope
-            .open(&password_derived_key, &server_s_pk_bytes, &optional_ids)
+            .open(
+                &password_derived_key,
+                &server_s_pk_bytes,
+                &params.identifiers,
+            )
             .map_err(|e| match e {
                 ProtocolError::LibraryError(InternalError::SealOpenHmacError) => {
                     ProtocolError::InvalidLoginError
@@ -702,7 +723,7 @@ impl<CS: CipherSuite> ClientLogin<CS> {
             opened_envelope.client_static_keypair.private().clone(),
             opened_envelope.id_u.clone(),
             opened_envelope.id_s.clone(),
-            context,
+            params.context.unwrap_or_default(),
         )?;
 
         Ok(ClientLoginFinishResult {
@@ -1007,12 +1028,19 @@ impl<CS: CipherSuite> Drop for ServerLogin<CS> {
 
 // Helper functions
 
-fn get_password_derived_key<G: Group, SH: SlowHash<D>, D: Hash>(
-    token: &oprf::Token<G>,
-    beta: G,
+fn get_password_derived_key<CS: CipherSuite>(
+    token: &oprf::Token<CS::OprfGroup>,
+    beta: CS::OprfGroup,
+    slow_hash: Option<&CS::SlowHash>,
 ) -> Result<Vec<u8>, ProtocolError> {
-    let oprf_output = oprf::finalize::<G, D>(&token.data, &token.blind, beta)?;
-    SH::hash(oprf_output).map_err(ProtocolError::from)
+    let oprf_output = oprf::finalize::<CS::OprfGroup, CS::Hash>(&token.data, &token.blind, beta)?;
+
+    if let Some(slow_hash) = slow_hash {
+        slow_hash.hash(oprf_output)
+    } else {
+        CS::SlowHash::default().hash(oprf_output)
+    }
+    .map_err(ProtocolError::from)
 }
 
 fn oprf_key_from_seed<G: Group, D: Hash>(
diff --git a/src/slow_hash.rs b/src/slow_hash.rs
index 19ce0e9..281dce7 100644
--- a/src/slow_hash.rs
+++ b/src/slow_hash.rs
@@ -13,33 +13,35 @@ use generic_array::typenum::Unsigned;
 use generic_array::GenericArray;
 
 /// Used for the slow hashing function in OPAQUE
-pub trait SlowHash<D: Hash> {
+pub trait SlowHash<D: Hash>: Default {
     /// Computes the slow hashing function
-    fn hash(input: GenericArray<u8, <D as Digest>::OutputSize>) -> Result<Vec<u8>, InternalError>;
+    fn hash(
+        &self,
+        input: GenericArray<u8, <D as Digest>::OutputSize>,
+    ) -> Result<Vec<u8>, InternalError>;
 }
 
 /// A no-op hash which simply returns its input
+#[derive(Default)]
 pub struct NoOpHash;
 
 impl<D: Hash> SlowHash<D> for NoOpHash {
-    fn hash(input: GenericArray<u8, <D as Digest>::OutputSize>) -> Result<Vec<u8>, InternalError> {
+    fn hash(
+        &self,
+        input: GenericArray<u8, <D as Digest>::OutputSize>,
+    ) -> Result<Vec<u8>, InternalError> {
         Ok(input.to_vec())
     }
 }
 
 #[cfg(feature = "slow-hash")]
 impl<D: Hash> SlowHash<D> for argon2::Argon2<'_> {
-    fn hash(input: GenericArray<u8, <D as Digest>::OutputSize>) -> Result<Vec<u8>, InternalError> {
-        let params = argon2::Argon2::default();
+    fn hash(
+        &self,
+        input: GenericArray<u8, <D as Digest>::OutputSize>,
+    ) -> Result<Vec<u8>, InternalError> {
         let mut output = alloc::vec![0u8; <D as Digest>::OutputSize::USIZE];
-        params
-            .hash_password_into(
-                argon2::Algorithm::Argon2id,
-                &input,
-                &[0; argon2::MIN_SALT_LENGTH],
-                &[],
-                &mut output,
-            )
+        self.hash_password_into(&input, &[0; argon2::MIN_SALT_LEN], &mut output)
             .map_err(|_| InternalError::SlowHashError)?;
         Ok(output)
     }
diff --git a/src/tests/full_test.rs b/src/tests/full_test.rs
index 28c58cc..a42c8bc 100644
--- a/src/tests/full_test.rs
+++ b/src/tests/full_test.rs
@@ -347,8 +347,12 @@ fn generate_parameters<CS: CipherSuite>() -> TestVectorParameters {
         .finish(
             &mut finish_registration_rng,
             server_registration_start_result.message,
-            ClientRegistrationFinishParameters::WithIdentifiers(
-                Identifiers::ClientAndServerIdentifiers(id_u.to_vec(), id_s.to_vec()),
+            ClientRegistrationFinishParameters::new(
+                Some(Identifiers::ClientAndServerIdentifiers(
+                    id_u.to_vec(),
+                    id_s.to_vec(),
+                )),
+                None,
             ),
         )
         .unwrap();
@@ -402,9 +406,13 @@ fn generate_parameters<CS: CipherSuite>() -> TestVectorParameters {
         .state
         .finish(
             server_login_start_result.message,
-            ClientLoginFinishParameters::WithContextAndIdentifiers(
-                context.to_vec(),
-                Identifiers::ClientAndServerIdentifiers(id_u.to_vec(), id_s.to_vec()),
+            ClientLoginFinishParameters::new(
+                Some(context.to_vec()),
+                Some(Identifiers::ClientAndServerIdentifiers(
+                    id_u.to_vec(),
+                    id_s.to_vec(),
+                )),
+                None,
             ),
         )
         .unwrap();
@@ -544,8 +552,12 @@ fn test_registration_upload() -> Result<(), ProtocolError> {
     .finish(
         &mut finish_registration_rng,
         RegistrationResponse::deserialize(&parameters.registration_response[..])?,
-        ClientRegistrationFinishParameters::WithIdentifiers(
-            Identifiers::ClientAndServerIdentifiers(parameters.id_u, parameters.id_s),
+        ClientRegistrationFinishParameters::new(
+            Some(Identifiers::ClientAndServerIdentifiers(
+                parameters.id_u,
+                parameters.id_s,
+            )),
+            None,
         ),
     )?;
 
@@ -662,9 +674,13 @@ fn test_credential_finalization() -> Result<(), ProtocolError> {
         CredentialResponse::<RistrettoSha5123dhNoSlowHash>::deserialize(
             &parameters.credential_response[..],
         )?,
-        ClientLoginFinishParameters::WithContextAndIdentifiers(
-            parameters.context,
-            Identifiers::ClientAndServerIdentifiers(parameters.id_u, parameters.id_s),
+        ClientLoginFinishParameters::new(
+            Some(parameters.context),
+            Some(Identifiers::ClientAndServerIdentifiers(
+                parameters.id_u,
+                parameters.id_s,
+            )),
+            None,
         ),
     )?;
 
diff --git a/src/tests/opaque_test_vectors.rs b/src/tests/opaque_test_vectors.rs
index 106eb2b..1971813 100644
--- a/src/tests/opaque_test_vectors.rs
+++ b/src/tests/opaque_test_vectors.rs
@@ -881,8 +881,8 @@ fn test_registration_upload<CS: CipherSuite>(tvs: &[&str]) -> Result<(), Protoco
             &mut finish_registration_rng,
             RegistrationResponse::deserialize(&parameters.registration_response[..]).unwrap(),
             match parse_identifiers(parameters.client_identity, parameters.server_identity) {
-                None => ClientRegistrationFinishParameters::Default,
-                Some(ids) => ClientRegistrationFinishParameters::WithIdentifiers(ids),
+                None => ClientRegistrationFinishParameters::default(),
+                Some(ids) => ClientRegistrationFinishParameters::new(Some(ids), None),
             },
         )?;
 
@@ -998,9 +998,9 @@ fn test_ke3<CS: CipherSuite>(tvs: &[&str]) -> Result<(), ProtocolError> {
         let client_login_finish_result = client_login_start_result.state.finish(
             CredentialResponse::<CS>::deserialize(&parameters.KE2[..])?,
             match parse_identifiers(parameters.client_identity, parameters.server_identity) {
-                None => ClientLoginFinishParameters::WithContext(parameters.context),
+                None => ClientLoginFinishParameters::new(Some(parameters.context), None, None),
                 Some(ids) => {
-                    ClientLoginFinishParameters::WithContextAndIdentifiers(parameters.context, ids)
+                    ClientLoginFinishParameters::new(Some(parameters.context), Some(ids), None)
                 }
             },
         )?;