diff --git a/Cargo.lock b/Cargo.lock
index f830002..66e9d0b 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -244,7 +244,7 @@ dependencies = [
  "futures-lite 2.2.0",
  "parking",
  "polling 3.3.2",
- "rustix 0.38.30",
+ "rustix 0.38.31",
  "slab",
  "tracing",
  "windows-sys 0.52.0",
@@ -1610,7 +1610,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "0bad00257d07be169d870ab665980b06cdb366d792ad690bf2e76876dc503455"
 dependencies = [
  "hermit-abi",
- "rustix 0.38.30",
+ "rustix 0.38.31",
  "windows-sys 0.52.0",
 ]
 
@@ -1870,6 +1870,7 @@ dependencies = [
  "keyfork-slip10-test-data",
  "keyforkd-models",
  "serde",
+ "tempfile",
  "thiserror",
  "tokio",
  "tower",
@@ -2533,7 +2534,7 @@ dependencies = [
  "cfg-if",
  "concurrent-queue",
  "pin-project-lite",
- "rustix 0.38.30",
+ "rustix 0.38.31",
  "tracing",
  "windows-sys 0.52.0",
 ]
@@ -2806,9 +2807,9 @@ dependencies = [
 
 [[package]]
 name = "rustix"
-version = "0.38.30"
+version = "0.38.31"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "322394588aaf33c24007e8bb3238ee3e4c5c09c084ab32bc73890b99ff326bca"
+checksum = "6ea3e1a662af26cd7a3ba09c0297a31af215563ecf42817c98df621387f4e949"
 dependencies = [
  "bitflags 2.4.2",
  "errno",
@@ -3184,14 +3185,13 @@ dependencies = [
 
 [[package]]
 name = "tempfile"
-version = "3.9.0"
+version = "3.10.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "01ce4141aa927a6d1bd34a041795abd0db1cccba5d5f24b009f694bdf3a1f3fa"
+checksum = "a365e8cd18e44762ef95d87f284f4b5cd04107fec2ff3052bd6a3e6069669e67"
 dependencies = [
  "cfg-if",
  "fastrand 2.0.1",
- "redox_syscall",
- "rustix 0.38.30",
+ "rustix 0.38.31",
  "windows-sys 0.52.0",
 ]
 
@@ -3212,7 +3212,7 @@ version = "0.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "21bebf2b7c9e0a515f6e0f8c51dc0f8e4696391e6f1ff30379559f8365fb0df7"
 dependencies = [
- "rustix 0.38.30",
+ "rustix 0.38.31",
  "windows-sys 0.48.0",
 ]
 
@@ -3606,7 +3606,7 @@ dependencies = [
  "either",
  "home",
  "once_cell",
- "rustix 0.38.30",
+ "rustix 0.38.31",
 ]
 
 [[package]]
diff --git a/crates/daemon/keyforkd-client/src/lib.rs b/crates/daemon/keyforkd-client/src/lib.rs
index 2362895..8ba4e79 100644
--- a/crates/daemon/keyforkd-client/src/lib.rs
+++ b/crates/daemon/keyforkd-client/src/lib.rs
@@ -2,8 +2,13 @@
 
 use std::{collections::HashMap, os::unix::net::UnixStream, path::PathBuf};
 
+use keyfork_derive_util::{
+    request::{AsAlgorithm, DerivationRequest},
+    DerivationPath, ExtendedPrivateKey, PrivateKey,
+};
+
 use keyfork_frame::{try_decode_from, try_encode_to, DecodeError, EncodeError};
-use keyforkd_models::{Request, Response, Error as KeyforkdError};
+use keyforkd_models::{Error as KeyforkdError, Request, Response};
 
 #[cfg(test)]
 mod tests;
@@ -11,6 +16,10 @@ mod tests;
 /// An error occurred while interacting with Keyforkd.
 #[derive(Debug, thiserror::Error)]
 pub enum Error {
+    /// The response from the server did not match the request.
+    #[error("The response from the server did not match the request")]
+    InvalidResponse,
+
     /// The environment variables used for determining a Keyforkd socket path were not set.
     #[error("Neither KEYFORK_SOCKET_PATH nor XDG_RUNTIME_DIR were set")]
     EnvVarsNotFound,
@@ -37,7 +46,7 @@ pub enum Error {
 
     /// An error encountered in Keyforkd.
     #[error("Error in Keyforkd: {0}")]
-    Keyforkd(#[from] KeyforkdError)
+    Keyforkd(#[from] KeyforkdError),
 }
 
 #[allow(missing_docs)]
@@ -95,6 +104,38 @@ impl Client {
         get_socket().map(|socket| Self { socket })
     }
 
+    /// Request an [`ExtendedPrivateKey`] for a given [`DerivationPath`].
+    ///
+    /// # Errors
+    /// An error may be returned if:
+    /// * Reading or writing from or to the socket encountered an error.
+    /// * Bincode could not serialize the request or deserialize the response.
+    /// * An error occurred in Keyforkd.
+    /// * Keyforkd returned invalid data.
+    pub fn request_xprv<K>(&mut self, path: &DerivationPath) -> Result<ExtendedPrivateKey<K>>
+    where
+        K: PrivateKey + Clone + AsAlgorithm,
+    {
+        let algo = K::as_algorithm();
+        let request = Request::Derivation(DerivationRequest::new(algo.clone(), path));
+        let response = self.request(&request)?;
+        match response {
+            Response::Derivation(d) => {
+                if d.algorithm != algo {
+                    return Err(Error::InvalidResponse);
+                }
+
+                let depth = path.len() as u8;
+                Ok(ExtendedPrivateKey::new_from_parts(
+                    &d.data,
+                    depth,
+                    d.chain_code,
+                ))
+            }
+            _ => Err(Error::InvalidResponse),
+        }
+    }
+
     /// Serialize and send a [`Request`] to the server, awaiting a [`Result<Response>`].
     ///
     /// # Errors
diff --git a/crates/daemon/keyforkd-client/src/tests.rs b/crates/daemon/keyforkd-client/src/tests.rs
index a3aabfb..7dae50c 100644
--- a/crates/daemon/keyforkd-client/src/tests.rs
+++ b/crates/daemon/keyforkd-client/src/tests.rs
@@ -1,100 +1,65 @@
 use crate::Client;
+use keyforkd::test_util::{run_test, Infallible};
 use keyfork_derive_util::{request::*, DerivationPath};
 use keyfork_slip10_test_data::test_data;
-use std::sync::mpsc::channel;
 use std::{os::unix::net::UnixStream, str::FromStr};
-use tokio::runtime::Builder;
 
 #[test]
-fn secp256k1() {
+fn secp256k1_test_suite() {
     let tests = test_data()
         .unwrap()
         .remove(&"secp256k1".to_string())
         .unwrap();
 
-    // note: since client is non async, can't be single threaded
-    let rt = Builder::new_multi_thread().enable_io().build().unwrap();
-    let tempdir = tempfile::tempdir().unwrap();
-    for (i, per_seed) in tests.into_iter().enumerate() {
-        let mut socket_name = i.to_string();
-        socket_name.push_str("-keyforkd.sock");
-        let socket_path = tempdir.path().join(socket_name);
-        let (tx, rx) = channel();
-        let handle = rt.spawn({
-            let socket_path = socket_path.clone();
-            async move {
-                let seed = per_seed.seed.clone();
-                let mut server = keyforkd::UnixServer::bind(&socket_path).unwrap();
-                tx.send(()).unwrap();
-                let service = keyforkd::ServiceBuilder::new()
-                    .layer(keyforkd::middleware::BincodeLayer::new())
-                    .service(keyforkd::Keyforkd::new(seed));
-                server.run(service).await.unwrap();
+    for seed_test in tests {
+        let seed = seed_test.seed;
+        run_test(&seed, move |socket_path| {
+            for test in seed_test.tests {
+                let socket = UnixStream::connect(&socket_path).unwrap();
+                let mut client = Client::new(socket);
+                let chain = DerivationPath::from_str(test.chain).unwrap();
+                if chain.len() < 2 {
+                    continue;
+                }
+                let req = DerivationRequest::new(
+                    DerivationAlgorithm::Secp256k1,
+                    &DerivationPath::from_str(test.chain).unwrap(),
+                );
+                let response =
+                    DerivationResponse::try_from(client.request(&req.into()).unwrap()).unwrap();
+                assert_eq!(&response.data, test.private_key.as_slice());
             }
-        });
-        rx.recv().unwrap();
-
-        for test in &per_seed.tests {
-            let socket = UnixStream::connect(&socket_path).unwrap();
-            let mut client = Client::new(socket);
-            let chain = DerivationPath::from_str(test.chain).unwrap();
-            if chain.len() < 2 {
-                continue;
-            }
-            let req = DerivationRequest::new(
-                DerivationAlgorithm::Secp256k1,
-                &DerivationPath::from_str(test.chain).unwrap(),
-            );
-            let response =
-                DerivationResponse::try_from(client.request(&req.into()).unwrap()).unwrap();
-            assert_eq!(response.data, test.private_key);
-        }
-
-        handle.abort();
+            Infallible::Ok(())
+        }).unwrap();
     }
 }
 
 #[test]
-fn ed25519() {
-    let tests = test_data().unwrap().remove(&"ed25519".to_string()).unwrap();
+fn ed25519_test_suite() {
+    let tests = test_data()
+        .unwrap()
+        .remove(&"ed25519".to_string())
+        .unwrap();
 
-    let rt = Builder::new_multi_thread().enable_io().build().unwrap();
-    let tempdir = tempfile::tempdir().unwrap();
-    for (i, per_seed) in tests.into_iter().enumerate() {
-        let mut socket_name = i.to_string();
-        socket_name.push_str("-keyforkd.sock");
-        let socket_path = tempdir.path().join(socket_name);
-        let (tx, rx) = channel();
-        let handle = rt.spawn({
-            let socket_path = socket_path.clone();
-            async move {
-                let seed = per_seed.seed.clone();
-                let mut server = keyforkd::UnixServer::bind(&socket_path).unwrap();
-                tx.send(()).unwrap();
-                let service = keyforkd::ServiceBuilder::new()
-                    .layer(keyforkd::middleware::BincodeLayer::new())
-                    .service(keyforkd::Keyforkd::new(seed));
-                server.run(service).await.unwrap();
+    for seed_test in tests {
+        let seed = seed_test.seed;
+        run_test(&seed, move |socket_path| {
+            for test in seed_test.tests {
+                let socket = UnixStream::connect(&socket_path).unwrap();
+                let mut client = Client::new(socket);
+                let chain = DerivationPath::from_str(test.chain).unwrap();
+                if chain.len() < 2 {
+                    continue;
+                }
+                let req = DerivationRequest::new(
+                    DerivationAlgorithm::Ed25519,
+                    &DerivationPath::from_str(test.chain).unwrap(),
+                );
+                let response =
+                    DerivationResponse::try_from(client.request(&req.into()).unwrap()).unwrap();
+                assert_eq!(&response.data, test.private_key.as_slice());
             }
-        });
-        rx.recv().unwrap();
-
-        for test in &per_seed.tests {
-            let socket = UnixStream::connect(&socket_path).unwrap();
-            let mut client = Client::new(socket);
-            let chain = DerivationPath::from_str(test.chain).unwrap();
-            if chain.len() < 2 {
-                continue;
-            }
-            let req = DerivationRequest::new(
-                DerivationAlgorithm::Ed25519,
-                &DerivationPath::from_str(test.chain).unwrap(),
-            );
-            let response =
-                DerivationResponse::try_from(client.request(&req.into()).unwrap()).unwrap();
-            assert_eq!(response.data, test.private_key);
-        }
-
-        handle.abort();
+            Infallible::Ok(())
+        }).unwrap();
     }
 }
diff --git a/crates/daemon/keyforkd/Cargo.toml b/crates/daemon/keyforkd/Cargo.toml
index 158f810..7813fd0 100644
--- a/crates/daemon/keyforkd/Cargo.toml
+++ b/crates/daemon/keyforkd/Cargo.toml
@@ -31,6 +31,7 @@ tower = { version = "0.4.13", features = ["tokio", "util"] }
 # Personally audited
 thiserror = "1.0.47"
 serde = { version = "1.0.186", features = ["derive"] }
+tempfile = { version = "3.10.0", default-features = false }
 
 [dev-dependencies]
 hex-literal = "0.4.1"
diff --git a/crates/daemon/keyforkd/src/lib.rs b/crates/daemon/keyforkd/src/lib.rs
index 4ea3a45..2fa0b20 100644
--- a/crates/daemon/keyforkd/src/lib.rs
+++ b/crates/daemon/keyforkd/src/lib.rs
@@ -30,6 +30,8 @@ pub use error::Keyforkd as KeyforkdError;
 pub use server::UnixServer;
 pub use service::Keyforkd;
 
+pub mod test_util;
+
 /// Set up a Tracing subscriber, defaulting to debug mode.
 #[cfg(feature = "tracing")]
 pub fn setup_registry() {
diff --git a/crates/daemon/keyforkd/src/service.rs b/crates/daemon/keyforkd/src/service.rs
index 1b4058b..fee1cad 100644
--- a/crates/daemon/keyforkd/src/service.rs
+++ b/crates/daemon/keyforkd/src/service.rs
@@ -76,7 +76,7 @@ impl Service<Request> for Keyforkd {
                     info!("Deriving path: {}", req.path());
                 }
 
-                req.derive_with_master_seed((*seed).clone())
+                req.derive_with_master_seed(seed.as_ref())
                     .map(Response::Derivation)
                     .map_err(|e| DerivationError::Derivation(e.to_string()).into())
             }),
@@ -120,7 +120,7 @@ mod tests {
                     .unwrap()
                     .try_into()
                     .unwrap();
-                assert_eq!(response.data, test.private_key);
+                assert_eq!(&response.data, test.private_key.as_slice());
                 assert_eq!(response.chain_code.as_slice(), test.chain_code);
             }
         }
@@ -150,7 +150,7 @@ mod tests {
                     .unwrap()
                     .try_into()
                     .unwrap();
-                assert_eq!(response.data, test.private_key);
+                assert_eq!(&response.data, test.private_key.as_slice());
                 assert_eq!(response.chain_code.as_slice(), test.chain_code);
             }
         }
diff --git a/crates/daemon/keyforkd/src/test_util.rs b/crates/daemon/keyforkd/src/test_util.rs
new file mode 100644
index 0000000..5e7fdb7
--- /dev/null
+++ b/crates/daemon/keyforkd/src/test_util.rs
@@ -0,0 +1,85 @@
+//! # Keyforkd Test Utilities
+//!
+//! This module adds a helper to set up a Tokio runtime, start a Tokio runtime with a given seed,
+//! start a Keyfork server on that runtime, and run a given test closure.
+
+use crate::{middleware, Keyforkd, ServiceBuilder, UnixServer};
+
+use tokio::runtime::Builder;
+
+#[derive(Debug, thiserror::Error)]
+#[error("This error can never be instantiated")]
+#[doc(hidden)]
+pub struct InfallibleError {
+    protected: (),
+}
+
+/// An infallible result. This type can be used to represent a function that should never error.
+///
+/// ```rust
+/// use keyforkd::test_util::Infallible;
+/// let closure = || {
+///     Infallible::Ok(())
+/// };
+/// assert!(closure().is_ok());
+/// ```
+pub type Infallible<T> = std::result::Result<T, InfallibleError>;
+
+/// Run a test making use of a Keyforkd server. The path to the socket of the Keyforkd server is
+/// provided as the only argument to the closure. The closure is expected to return a Result; the
+/// Error field of the Result may be an error returned by a test.
+///
+/// # Panics
+///
+/// The function is not expected to run in production; therefore, the function plays "fast and
+/// loose" wih the usage of [`Result::expect`]. In normal usage, these should never be an issue.
+#[allow(clippy::missing_errors_doc)]
+pub fn run_test<F, E>(seed: &[u8], closure: F) -> Result<(), E>
+where
+    F: FnOnce(&std::path::Path) -> Result<(), E> + Send + 'static,
+    E: Send + 'static,
+{
+    let rt = Builder::new_multi_thread()
+        .worker_threads(2)
+        .enable_io()
+        .build()
+        .expect("tokio threaded IO runtime");
+    let socket_dir = tempfile::tempdir().expect("can't create tempdir");
+    let socket_path = socket_dir.path().join("keyforkd.sock");
+    rt.block_on(async move {
+        let (tx, mut rx) = tokio::sync::mpsc::channel(1);
+        let server_handle = tokio::spawn({
+            let socket_path = socket_path.clone();
+            let seed = seed.to_vec();
+            async move {
+                let mut server = UnixServer::bind(&socket_path).expect("can't bind unix socket");
+                tx.send(()).await.expect("couldn't send server start signal");
+                let service = ServiceBuilder::new()
+                    .layer(middleware::BincodeLayer::new())
+                    .service(Keyforkd::new(seed.to_vec()));
+                server.run(service).await.unwrap();
+            }
+        });
+
+        rx.recv()
+            .await
+            .expect("can't receive server start signal from channel");
+        let test_handle = tokio::task::spawn_blocking(move || closure(&socket_path));
+
+        let result = test_handle.await;
+        server_handle.abort();
+        result
+    })
+    .expect("runtime could not join all threads")
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_run_test() {
+        let seed = b"beefbeef";
+        run_test(seed, |_path| Infallible::Ok(())).expect("infallible");
+    }
+}
diff --git a/crates/derive/keyfork-derive-openpgp/src/lib.rs b/crates/derive/keyfork-derive-openpgp/src/lib.rs
index 2055734..1292ca7 100644
--- a/crates/derive/keyfork-derive-openpgp/src/lib.rs
+++ b/crates/derive/keyfork-derive-openpgp/src/lib.rs
@@ -2,13 +2,10 @@
 
 use std::time::{Duration, SystemTime, SystemTimeError};
 
-use derive_util::{
-    request::{DerivationResponse, TryFromDerivationResponseError},
-    DerivationIndex, ExtendedPrivateKey, PrivateKey,
-    IndexError,
-};
+use derive_util::{DerivationIndex, ExtendedPrivateKey, IndexError, PrivateKey};
 use ed25519_dalek::SigningKey;
 pub use keyfork_derive_util as derive_util;
+pub use sequoia_openpgp as openpgp;
 use sequoia_openpgp::{
     packet::{
         key::{Key4, PrimaryRole, SubordinateRole},
@@ -18,7 +15,9 @@ use sequoia_openpgp::{
     types::{KeyFlags, SignatureType},
     Cert, Packet,
 };
-pub use sequoia_openpgp as openpgp;
+
+pub type XPrvKey = SigningKey;
+pub type XPrv = ExtendedPrivateKey<SigningKey>;
 
 /// An error occurred while creating an OpenPGP key.
 #[derive(Debug, thiserror::Error)]
@@ -32,10 +31,6 @@ pub enum Error {
     #[error("Key configured with both encryption and non-encryption key flags: {0:?}")]
     InvalidKeyFlags(KeyFlags),
 
-    /// The derivation response contained incorrect data.
-    #[error("Incorrect derived data: {0}")]
-    IncorrectDerivedData(#[from] TryFromDerivationResponseError),
-
     /// A derivation index could not be created from the given index.
     #[error("Could not create derivation index: {0}")]
     Index(#[from] IndexError),
@@ -66,7 +61,7 @@ pub type Result<T, E = Error> = std::result::Result<T, E>;
 ///
 /// # Errors
 /// The function may error for any condition mentioned in [`Error`].
-pub fn derive(data: DerivationResponse, keys: &[KeyFlags], userid: &UserID) -> Result<Cert> {
+pub fn derive(xprv: XPrv, keys: &[KeyFlags], userid: &UserID) -> Result<Cert> {
     let primary_key_flags = match keys.get(0) {
         Some(kf) if kf.for_certification() => kf,
         _ => return Err(Error::NotCert),
@@ -76,7 +71,6 @@ pub fn derive(data: DerivationResponse, keys: &[KeyFlags], userid: &UserID) -> R
     let one_day = SystemTime::now() + Duration::from_secs(60 * 60 * 24);
 
     // Create certificate with initial key and signature
-    let xprv = ExtendedPrivateKey::<SigningKey>::try_from(data)?;
     let derived_primary_key = xprv.derive_child(&DerivationIndex::new(0, true)?)?;
     let primary_key = Key::from(Key4::<_, PrimaryRole>::import_secret_ed25519(
         &PrivateKey::to_bytes(derived_primary_key.private_key()),
@@ -118,21 +112,14 @@ pub fn derive(data: DerivationResponse, keys: &[KeyFlags], userid: &UserID) -> R
             bytes[0] &= 0b1111_1000;
             bytes[31] &= !0b1000_0000;
             bytes[31] |= 0b0100_0000;
-            Key::from(
-                Key4::<_, SubordinateRole>::import_secret_cv25519(
-                    &bytes,
-                    None,
-                    None,
-                    epoch,
-                )?
-            )
+            Key::from(Key4::<_, SubordinateRole>::import_secret_cv25519(
+                &bytes, None, None, epoch,
+            )?)
         } else {
-            Key::from(
-                Key4::<_, SubordinateRole>::import_secret_ed25519(
-                    &PrivateKey::to_bytes(derived_key.private_key()),
-                    epoch,
-                )?
-            )
+            Key::from(Key4::<_, SubordinateRole>::import_secret_ed25519(
+                &PrivateKey::to_bytes(derived_key.private_key()),
+                epoch,
+            )?)
         };
 
         // As per OpenPGP spec, signing keys must backsig the primary key
diff --git a/crates/derive/keyfork-derive-openpgp/src/main.rs b/crates/derive/keyfork-derive-openpgp/src/main.rs
index 3aec137..8431b17 100644
--- a/crates/derive/keyfork-derive-openpgp/src/main.rs
+++ b/crates/derive/keyfork-derive-openpgp/src/main.rs
@@ -2,12 +2,16 @@
 
 use std::{env, process::ExitCode, str::FromStr};
 
-use keyfork_derive_util::{
-    request::{DerivationAlgorithm, DerivationRequest, DerivationResponse},
-    DerivationIndex, DerivationPath,
-};
+use keyfork_derive_util::{DerivationIndex, DerivationPath};
 use keyforkd_client::Client;
-use sequoia_openpgp::{packet::UserID, types::KeyFlags, armor::{Kind, Writer}, serialize::Marshal};
+
+use ed25519_dalek::SigningKey;
+use sequoia_openpgp::{
+    armor::{Kind, Writer},
+    packet::UserID,
+    serialize::Marshal,
+    types::KeyFlags,
+};
 
 #[derive(Debug, thiserror::Error)]
 enum Error {
@@ -108,16 +112,13 @@ fn run() -> Result<(), Box<dyn std::error::Error>> {
         _ => panic!("Usage: {program_name} path subkey_format default_userid"),
     };
 
-    let request = DerivationRequest::new(DerivationAlgorithm::Ed25519, &path);
-    let derived_data: DerivationResponse = Client::discover_socket()?
-        .request(&request.into())?
-        .try_into()?;
+    let derived_xprv = Client::discover_socket()?.request_xprv::<SigningKey>(&path)?;
     let subkeys = subkey_format
         .iter()
         .map(|kt| kt.inner().clone())
         .collect::<Vec<_>>();
 
-    let cert = keyfork_derive_openpgp::derive(derived_data, subkeys.as_slice(), &default_userid)?;
+    let cert = keyfork_derive_openpgp::derive(derived_xprv, subkeys.as_slice(), &default_userid)?;
 
     let mut w = Writer::new(std::io::stdout(), Kind::SecretKey)?;
 
diff --git a/crates/derive/keyfork-derive-util/README.md b/crates/derive/keyfork-derive-util/README.md
index 20135ff..55fb1e1 100644
--- a/crates/derive/keyfork-derive-util/README.md
+++ b/crates/derive/keyfork-derive-util/README.md
@@ -40,7 +40,7 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
     let key1 = request.derive_with_mnemonic(&mnemonic)?;
 
     let seed = mnemonic.seed(None)?;
-    let key2 = request.derive_with_master_seed(seed)?;
+    let key2 = request.derive_with_master_seed(&seed)?;
 
     assert_eq!(key1, key2);
 
diff --git a/crates/derive/keyfork-derive-util/src/extended_key/private_key.rs b/crates/derive/keyfork-derive-util/src/extended_key/private_key.rs
index 1bbf3ca..ad15994 100644
--- a/crates/derive/keyfork-derive-util/src/extended_key/private_key.rs
+++ b/crates/derive/keyfork-derive-util/src/extended_key/private_key.rs
@@ -10,18 +10,10 @@ const KEY_SIZE: usize = 256;
 /// Errors associated with creating or deriving Extended Private Keys.
 #[derive(Error, Clone, Debug)]
 pub enum Error {
-    /// The seed has an unsuitable length; supported lengths are 16 bytes, 32 bytes, or 64 bytes.
-    #[error("Seed had an unsuitable length: {0}")]
-    BadSeedLength(usize),
-
     /// The maximum depth for key derivation has been reached. The supported maximum depth is 255.
     #[error("Reached maximum depth for key derivation")]
     Depth,
 
-    /// This should never happen. HMAC keys should be able to take any size input.
-    #[error("Invalid length for HMAC key while generating master key (report me!)")]
-    HmacInvalidLength(#[from] hmac::digest::InvalidLength),
-
     /// An unknown error occurred while deriving a child key.
     #[error("Unknown error while deriving child key")]
     Derivation,
@@ -39,17 +31,104 @@ type Result<T, E = Error> = std::result::Result<T, E>;
 type ChainCode = [u8; 32];
 type HmacSha512 = Hmac<Sha512>;
 
+/// A reference to a variable-length seed. Keyfork automatically supports a seed of 128 bits,
+/// 256 bits, or 512 bits, but because the master key is derived from a hashed seed, in theory
+/// any amount of bytes could be used. It is not advised to use a variable-length seed longer
+/// than 256 bits, as a brute-force attack on the master key could be performed in 2^256
+/// attempts.
+///
+/// Mnemonics use a 512 bit seed, as knowledge of the mnemonics' words (such as through a side
+/// channel attack) could leak which individual word is used, but not the order the words are
+/// used in. Using a 512 bit hash to generate the seed results in a more computationally
+/// expensive brute-force requirement.
+pub struct VariableLengthSeed<'a> {
+    seed: &'a [u8],
+}
+
+impl<'a> VariableLengthSeed<'a> {
+    /// Create a new VariableLengthSeed.
+    ///
+    /// # Examples
+    /// ```rust
+    /// use sha2::{Sha256, Digest};
+    /// use keyfork_derive_util::VariableLengthSeed;
+    ///
+    /// let data = b"the missile is very eepy and wants to take a small sleeb";
+    /// let seed = VariableLengthSeed::new(data);
+    /// ```
+    pub fn new(seed: &'a [u8]) -> Self {
+        Self { seed }
+    }
+}
+
+mod as_private_key {
+    use super::VariableLengthSeed;
+
+    pub trait AsPrivateKey {
+        fn as_private_key(&self) -> &[u8];
+    }
+
+    impl AsPrivateKey for [u8; 16] {
+        fn as_private_key(&self) -> &[u8] {
+            self
+        }
+    }
+
+    impl AsPrivateKey for [u8; 32] {
+        fn as_private_key(&self) -> &[u8] {
+            self
+        }
+    }
+
+    impl AsPrivateKey for [u8; 64] {
+        fn as_private_key(&self) -> &[u8] {
+            self
+        }
+    }
+
+    impl AsPrivateKey for VariableLengthSeed<'_> {
+        fn as_private_key(&self) -> &[u8] {
+            self.seed
+        }
+    }
+}
+
 /// Extended private keys derived using BIP-0032.
 ///
 /// Generic over types implementing [`PrivateKey`].
 #[derive(Clone, Serialize, Deserialize)]
 pub struct ExtendedPrivateKey<K: PrivateKey + Clone> {
     /// The internal private key data.
+    #[serde(with = "serde_with")]
     private_key: K,
     depth: u8,
     chain_code: ChainCode,
 }
 
+mod serde_with {
+    use super::*;
+
+    pub(crate) fn serialize<S, K>(value: &K, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: serde::Serializer,
+        K: PrivateKey + Clone,
+    {
+        serializer.serialize_bytes(&value.to_bytes())
+    }
+
+    pub(crate) fn deserialize<'de, D, K>(deserializer: D) -> Result<K, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+        K: PrivateKey + Clone,
+    {
+        let variable_len_bytes = <&[u8]>::deserialize(deserializer)?;
+        let bytes: [u8; 32] = variable_len_bytes
+            .try_into()
+            .expect("unable to parse serialized private key; no support for static len");
+        Ok(K::from_bytes(&bytes))
+    }
+}
+
 impl<K: PrivateKey + Clone> std::fmt::Debug for ExtendedPrivateKey<K> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         f.debug_struct("ExtendedPrivateKey")
@@ -73,7 +152,7 @@ where
     /// # Errors
     /// An error may be returned if:
     /// * The given seed had an incorrect length.
-    /// * A `HmacSha512` can't be constructed - this should be impossible.
+    /// * A `HmacSha512` can't be constructed.
     ///
     /// # Examples
     /// ```rust
@@ -82,31 +161,26 @@ where
     /// #   public_key::TestPublicKey as PublicKey,
     /// #   private_key::TestPrivateKey as PrivateKey,
     /// # };
-    /// # fn main() -> Result<(), Box<dyn std::error::Error>> {
     /// let seed: &[u8; 64] = //
     /// #   b"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA";
-    /// let xprv = ExtendedPrivateKey::<PrivateKey>::new(seed)?;
-    /// # Ok(())
-    /// # }
+    /// let xprv = ExtendedPrivateKey::<PrivateKey>::new(*seed);
     /// ```
-    pub fn new(seed: impl AsRef<[u8]>) -> Result<Self> {
-        Self::new_internal(seed.as_ref())
+    pub fn new(seed: impl as_private_key::AsPrivateKey) -> Self {
+        Self::new_internal(seed.as_private_key())
     }
 
-    fn new_internal(seed: &[u8]) -> Result<Self> {
-        let len = seed.len();
-        if ![16, 32, 64].contains(&len) {
-            return Err(Error::BadSeedLength(len));
-        }
-
-        let hash = HmacSha512::new_from_slice(&K::key().bytes().collect::<Vec<_>>())?
+    fn new_internal(seed: &[u8]) -> Self {
+        let hash = HmacSha512::new_from_slice(&K::key().bytes().collect::<Vec<_>>())
+            .expect("HmacSha512 InvalidLength should be infallible")
             .chain_update(seed)
             .finalize()
             .into_bytes();
         let (private_key, chain_code) = hash.split_at(KEY_SIZE / 8);
 
         Self::new_from_parts(
-            private_key,
+            private_key
+                .try_into()
+                .expect("KEY_SIZE / 8 did not give a 32 byte slice"),
             0,
             // Checked: chain_code is always the same length, hash is static size
             chain_code.try_into().expect("Invalid chain code length"),
@@ -125,21 +199,18 @@ where
     /// #   public_key::TestPublicKey as PublicKey,
     /// #   private_key::TestPrivateKey as PrivateKey,
     /// # };
-    /// # fn main() -> Result<(), Box<dyn std::error::Error>> {
     /// let key: &[u8; 32] = //
     /// #   b"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA";
     /// let chain_code: &[u8; 32] = //
     /// #   b"BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB";
-    /// let xprv = ExtendedPrivateKey::<PrivateKey>::new_from_parts(key, 4, *chain_code)?;
-    /// # Ok(())
-    /// # }
+    /// let xprv = ExtendedPrivateKey::<PrivateKey>::new_from_parts(key, 4, *chain_code);
     /// ```
-    pub fn new_from_parts(seed: &[u8], depth: u8, chain_code: [u8; 32]) -> Result<Self> {
-        Ok(Self {
-            private_key: K::from_bytes(seed.try_into()?),
+    pub fn new_from_parts(key: &[u8; 32], depth: u8, chain_code: [u8; 32]) -> Self {
+        Self {
+            private_key: K::from_bytes(key),
             depth,
             chain_code,
-        })
+        }
     }
 
     /// Returns a reference to the [`PrivateKey`].
@@ -152,15 +223,12 @@ where
     /// #   public_key::TestPublicKey as PublicKey,
     /// #   private_key::TestPrivateKey as PrivateKey,
     /// # };
-    /// # fn main() -> Result<(), Box<dyn std::error::Error>> {
     /// let key: &[u8; 32] = //
     /// #   b"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA";
     /// let chain_code: &[u8; 32] = //
     /// #   b"BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB";
-    /// let xprv = ExtendedPrivateKey::<PrivateKey>::new_from_parts(key, 4, *chain_code)?;
+    /// let xprv = ExtendedPrivateKey::<PrivateKey>::new_from_parts(key, 4, *chain_code);
     /// assert_eq!(xprv.private_key(), &PrivateKey::from_bytes(key));
-    /// # Ok(())
-    /// # }
     /// ```
     pub fn private_key(&self) -> &K {
         &self.private_key
@@ -185,7 +253,7 @@ where
     /// # 102, 201, 210, 159, 219, 222, 42, 201, 44, 196, 27,
     /// # 90, 221, 80, 85, 135, 79, 39, 253, 223, 35, 251
     /// # ];
-    /// let xprv = ExtendedPrivateKey::<PrivateKey>::new(seed)?;
+    /// let xprv = ExtendedPrivateKey::<PrivateKey>::new(*seed);
     /// let xpub = xprv.extended_public_key();
     /// assert_eq!(known_key, xpub.public_key().to_bytes());
     /// # Ok(())
@@ -209,7 +277,7 @@ where
     /// # fn main() -> Result<(), Box<dyn std::error::Error>> {
     /// let seed: &[u8; 64] = //
     /// #   b"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA";
-    /// let xprv = ExtendedPrivateKey::<PrivateKey>::new(seed)?;
+    /// let xprv = ExtendedPrivateKey::<PrivateKey>::new(*seed);
     /// let pubkey = xprv.public_key();
     /// # Ok(())
     /// # }
@@ -227,15 +295,12 @@ where
     /// #   public_key::TestPublicKey as PublicKey,
     /// #   private_key::TestPrivateKey as PrivateKey,
     /// # };
-    /// # fn main() -> Result<(), Box<dyn std::error::Error>> {
     /// let key: &[u8; 32] = //
     /// #   b"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA";
     /// let chain_code: &[u8; 32] = //
     /// #   b"BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB";
-    /// let xprv = ExtendedPrivateKey::<PrivateKey>::new_from_parts(key, 4, *chain_code)?;
+    /// let xprv = ExtendedPrivateKey::<PrivateKey>::new_from_parts(key, 4, *chain_code);
     /// assert_eq!(xprv.depth(), 4);
-    /// # Ok(())
-    /// # }
     /// ```
     pub fn depth(&self) -> u8 {
         self.depth
@@ -250,15 +315,12 @@ where
     /// #   public_key::TestPublicKey as PublicKey,
     /// #   private_key::TestPrivateKey as PrivateKey,
     /// # };
-    /// # fn main() -> Result<(), Box<dyn std::error::Error>> {
     /// let key: &[u8; 32] = //
     /// #   b"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA";
     /// let chain_code: &[u8; 32] = //
     /// #   b"BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB";
-    /// let xprv = ExtendedPrivateKey::<PrivateKey>::new_from_parts(key, 4, *chain_code)?;
+    /// let xprv = ExtendedPrivateKey::<PrivateKey>::new_from_parts(key, 4, *chain_code);
     /// assert_eq!(chain_code, &xprv.chain_code());
-    /// # Ok(())
-    /// # }
     /// ```
     pub fn chain_code(&self) -> [u8; 32] {
         self.chain_code
@@ -280,7 +342,7 @@ where
     /// # fn main() -> Result<(), Box<dyn std::error::Error>> {
     /// let seed: &[u8; 64] = //
     /// #   b"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA";
-    /// let root_xprv = ExtendedPrivateKey::<PrivateKey>::new(seed)?;
+    /// let root_xprv = ExtendedPrivateKey::<PrivateKey>::new(*seed);
     /// let path = DerivationPath::default()
     ///     .chain_push(DerivationIndex::new(44, true)?)
     ///     .chain_push(DerivationIndex::new(0, true)?)
@@ -326,7 +388,7 @@ where
     /// # fn main() -> Result<(), Box<dyn std::error::Error>> {
     /// let seed: &[u8; 64] = //
     /// #   b"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA";
-    /// let root_xprv = ExtendedPrivateKey::<PrivateKey>::new(seed)?;
+    /// let root_xprv = ExtendedPrivateKey::<PrivateKey>::new(*seed);
     /// let bip44_wallet = DerivationPath::default()
     ///     .chain_push(DerivationIndex::new(44, true)?)
     ///     .chain_push(DerivationIndex::new(0, true)?)
@@ -342,8 +404,8 @@ where
     pub fn derive_child(&self, index: &DerivationIndex) -> Result<Self> {
         let depth = self.depth.checked_add(1).ok_or(Error::Depth)?;
 
-        let mut hmac =
-            HmacSha512::new_from_slice(&self.chain_code).map_err(Error::HmacInvalidLength)?;
+        let mut hmac = HmacSha512::new_from_slice(&self.chain_code)
+            .expect("HmacSha512 InvalidLength should be infallible");
         if index.is_hardened() {
             hmac.update(&[0]);
             hmac.update(&self.private_key.to_bytes());
diff --git a/crates/derive/keyfork-derive-util/src/lib.rs b/crates/derive/keyfork-derive-util/src/lib.rs
index ba170d4..ce2c1a7 100644
--- a/crates/derive/keyfork-derive-util/src/lib.rs
+++ b/crates/derive/keyfork-derive-util/src/lib.rs
@@ -17,7 +17,7 @@ pub mod public_key;
 mod tests;
 
 #[doc(inline)]
-pub use crate::extended_key::{private_key::ExtendedPrivateKey, public_key::ExtendedPublicKey};
+pub use crate::extended_key::{private_key::{ExtendedPrivateKey, Error as XPrvError, VariableLengthSeed}, public_key::{ExtendedPublicKey, Error as XPubError}};
 
 pub use crate::{
     index::{DerivationIndex, Error as IndexError},
diff --git a/crates/derive/keyfork-derive-util/src/request.rs b/crates/derive/keyfork-derive-util/src/request.rs
index 57fc810..d6f5830 100644
--- a/crates/derive/keyfork-derive-util/src/request.rs
+++ b/crates/derive/keyfork-derive-util/src/request.rs
@@ -19,10 +19,11 @@
 //! ```
 
 use crate::{
-    extended_key::private_key::Error as XPrvError,
+    extended_key::private_key::{Error as XPrvError, VariableLengthSeed},
     private_key::{PrivateKey, TestPrivateKey},
     DerivationPath, ExtendedPrivateKey,
 };
+
 use keyfork_mnemonic_util::{Mnemonic, MnemonicGenerationError};
 use serde::{Deserialize, Serialize};
 
@@ -64,11 +65,12 @@ impl DerivationAlgorithm {
     ///
     /// # Errors
     /// The method may error if the derivation fails or if the algorithm is not supported.
-    fn derive(&self, seed: Vec<u8>, path: &DerivationPath) -> Result<DerivationResponse> {
+    fn derive(&self, seed: &[u8], path: &DerivationPath) -> Result<DerivationResponse> {
+        let seed = VariableLengthSeed::new(seed);
         match self {
             #[cfg(feature = "ed25519")]
             Self::Ed25519 => {
-                let key = ExtendedPrivateKey::<ed25519_dalek::SigningKey>::new(seed)?;
+                let key = ExtendedPrivateKey::<ed25519_dalek::SigningKey>::new(seed);
                 let derived_key = key.derive_path(path)?;
                 Ok(DerivationResponse::with_algo_and_xprv(
                     self.clone(),
@@ -77,7 +79,7 @@ impl DerivationAlgorithm {
             }
             #[cfg(feature = "secp256k1")]
             Self::Secp256k1 => {
-                let key = ExtendedPrivateKey::<k256::SecretKey>::new(seed)?;
+                let key = ExtendedPrivateKey::<k256::SecretKey>::new(seed);
                 let derived_key = key.derive_path(path)?;
                 Ok(DerivationResponse::with_algo_and_xprv(
                     self.clone(),
@@ -85,7 +87,7 @@ impl DerivationAlgorithm {
                 ))
             }
             Self::Internal => {
-                let key = ExtendedPrivateKey::<TestPrivateKey>::new(seed)?;
+                let key = ExtendedPrivateKey::<TestPrivateKey>::new(seed);
                 let derived_key = key.derive_path(path)?;
                 Ok(DerivationResponse::with_algo_and_xprv(
                     self.clone(),
@@ -110,6 +112,18 @@ impl std::str::FromStr for DerivationAlgorithm {
     }
 }
 
+/// Acquire the associated [`DerivationAlgorithm`] for a [`PrivateKey`].
+pub trait AsAlgorithm: PrivateKey {
+    /// Return the appropriate [`DerivationAlgorithm`].
+    fn as_algorithm() -> DerivationAlgorithm;
+}
+
+impl AsAlgorithm for TestPrivateKey {
+    fn as_algorithm() -> DerivationAlgorithm {
+        DerivationAlgorithm::Internal
+    }
+}
+
 /// A derivation request.
 #[derive(Serialize, Deserialize, Clone, Debug, PartialEq, Eq)]
 pub struct DerivationRequest {
@@ -195,7 +209,7 @@ impl DerivationRequest {
     /// # }
     pub fn derive_with_mnemonic(&self, mnemonic: &Mnemonic) -> Result<DerivationResponse> {
         // TODO: passphrase support and/or store passphrase within mnemonic
-        self.derive_with_master_seed(mnemonic.seed(None)?)
+        self.derive_with_master_seed(&mnemonic.seed(None)?)
     }
 
     /// Derive an [`ExtendedPrivateKey`] using the given seed.
@@ -219,10 +233,10 @@ impl DerivationRequest {
     /// let path: DerivationPath = //
     /// #   DerivationPath::default();
     /// let request = DerivationRequest::new(algo, &path);
-    /// let response = request.derive_with_master_seed(seed.to_vec())?;
+    /// let response = request.derive_with_master_seed(seed)?;
     /// # Ok(())
     /// # }
-    pub fn derive_with_master_seed(&self, seed: Vec<u8>) -> Result<DerivationResponse> {
+    pub fn derive_with_master_seed(&self, seed: &[u8]) -> Result<DerivationResponse> {
         self.algorithm.derive(seed, &self.path)
     }
 }
@@ -234,7 +248,7 @@ pub struct DerivationResponse {
     pub algorithm: DerivationAlgorithm,
 
     /// The derived private key.
-    pub data: Vec<u8>,
+    pub data: [u8; 32],
 
     /// The chain code, used for further derivation.
     pub chain_code: [u8; 32],
@@ -251,7 +265,7 @@ impl DerivationResponse {
     ) -> Self {
         Self {
             algorithm,
-            data: PrivateKey::to_bytes(xprv.private_key()).to_vec(),
+            data: PrivateKey::to_bytes(xprv.private_key()),
             chain_code: xprv.chain_code(),
             depth: xprv.depth(),
         }
@@ -272,47 +286,71 @@ pub enum TryFromDerivationResponseError {
 }
 
 #[cfg(feature = "secp256k1")]
-impl TryFrom<&DerivationResponse> for ExtendedPrivateKey<k256::SecretKey> {
-    type Error = TryFromDerivationResponseError;
+mod secp256k1 {
+    use super::*;
+    use k256::SecretKey;
 
-    fn try_from(value: &DerivationResponse) -> std::result::Result<Self, Self::Error> {
-        match value.algorithm {
-            DerivationAlgorithm::Secp256k1 => {
-                Self::new_from_parts(&value.data, value.depth, value.chain_code).map_err(From::from)
-            }
-            _ => Err(Self::Error::Algorithm),
+    impl AsAlgorithm for SecretKey {
+        fn as_algorithm() -> DerivationAlgorithm {
+            DerivationAlgorithm::Secp256k1
         }
     }
-}
 
-#[cfg(feature = "secp256k1")]
-impl TryFrom<DerivationResponse> for ExtendedPrivateKey<k256::SecretKey> {
-    type Error = TryFromDerivationResponseError;
+    impl TryFrom<&DerivationResponse> for ExtendedPrivateKey<SecretKey> {
+        type Error = TryFromDerivationResponseError;
 
-    fn try_from(value: DerivationResponse) -> std::result::Result<Self, Self::Error> {
-        ExtendedPrivateKey::<k256::SecretKey>::try_from(&value)
-    }
-}
-
-#[cfg(feature = "ed25519")]
-impl TryFrom<&DerivationResponse> for ExtendedPrivateKey<ed25519_dalek::SigningKey> {
-    type Error = TryFromDerivationResponseError;
-
-    fn try_from(value: &DerivationResponse) -> std::result::Result<Self, Self::Error> {
-        match value.algorithm {
-            DerivationAlgorithm::Ed25519 => {
-                Self::new_from_parts(&value.data, value.depth, value.chain_code).map_err(From::from)
+        fn try_from(value: &DerivationResponse) -> Result<Self, Self::Error> {
+            match value.algorithm {
+                DerivationAlgorithm::Secp256k1 => Ok(Self::new_from_parts(
+                    &value.data,
+                    value.depth,
+                    value.chain_code,
+                )),
+                _ => Err(Self::Error::Algorithm),
             }
-            _ => Err(Self::Error::Algorithm),
+        }
+    }
+
+    impl TryFrom<DerivationResponse> for ExtendedPrivateKey<SecretKey> {
+        type Error = TryFromDerivationResponseError;
+
+        fn try_from(value: DerivationResponse) -> Result<Self, Self::Error> {
+            ExtendedPrivateKey::<SecretKey>::try_from(&value)
         }
     }
 }
 
 #[cfg(feature = "ed25519")]
-impl TryFrom<DerivationResponse> for ExtendedPrivateKey<ed25519_dalek::SigningKey> {
-    type Error = TryFromDerivationResponseError;
+mod ed25519 {
+    use super::*;
+    use ed25519_dalek::SigningKey;
 
-    fn try_from(value: DerivationResponse) -> std::result::Result<Self, Self::Error> {
-        ExtendedPrivateKey::<ed25519_dalek::SigningKey>::try_from(&value)
+    impl AsAlgorithm for SigningKey {
+        fn as_algorithm() -> DerivationAlgorithm {
+            DerivationAlgorithm::Ed25519
+        }
+    }
+
+    impl TryFrom<&DerivationResponse> for ExtendedPrivateKey<SigningKey> {
+        type Error = TryFromDerivationResponseError;
+
+        fn try_from(value: &DerivationResponse) -> Result<Self, Self::Error> {
+            match value.algorithm {
+                DerivationAlgorithm::Ed25519 => Ok(Self::new_from_parts(
+                    &value.data,
+                    value.depth,
+                    value.chain_code,
+                )),
+                _ => Err(Self::Error::Algorithm),
+            }
+        }
+    }
+
+    impl TryFrom<DerivationResponse> for ExtendedPrivateKey<SigningKey> {
+        type Error = TryFromDerivationResponseError;
+
+        fn try_from(value: DerivationResponse) -> Result<Self, Self::Error> {
+            ExtendedPrivateKey::<SigningKey>::try_from(&value)
+        }
     }
 }
diff --git a/crates/derive/keyfork-derive-util/src/tests.rs b/crates/derive/keyfork-derive-util/src/tests.rs
index f4238e3..3f2eba3 100644
--- a/crates/derive/keyfork-derive-util/src/tests.rs
+++ b/crates/derive/keyfork-derive-util/src/tests.rs
@@ -30,7 +30,8 @@ fn secp256k1() {
             } = test;
 
             // Tests for ExtendedPrivateKey
-            let xkey = ExtendedPrivateKey::<SecretKey>::new(seed).unwrap();
+            let varlen_seed = VariableLengthSeed::new(&seed);
+            let xkey = ExtendedPrivateKey::<SecretKey>::new(varlen_seed);
             let derived_key = xkey.derive_path(&chain).unwrap();
             assert_eq!(
                 derived_key.chain_code().as_slice(),
@@ -50,8 +51,8 @@ fn secp256k1() {
 
             // Tests for DerivationRequest
             let request = DerivationRequest::new(DerivationAlgorithm::Secp256k1, &chain);
-            let response = request.derive_with_master_seed(seed.clone()).unwrap();
-            assert_eq!(&response.data, private_key, "test: {chain}");
+            let response = request.derive_with_master_seed(&seed).unwrap();
+            assert_eq!(&response.data, private_key.as_slice(), "test: {chain}");
         }
     }
 }
@@ -75,7 +76,8 @@ fn ed25519() {
             } = test;
 
             // Tests for ExtendedPrivateKey
-            let xkey = ExtendedPrivateKey::<SigningKey>::new(seed).unwrap();
+            let varlen_seed = VariableLengthSeed::new(&seed);
+            let xkey = ExtendedPrivateKey::<SigningKey>::new(varlen_seed);
             let derived_key = xkey.derive_path(&chain).unwrap();
             assert_eq!(
                 derived_key.chain_code().as_slice(),
@@ -95,8 +97,8 @@ fn ed25519() {
 
             // Tests for DerivationRequest
             let request = DerivationRequest::new(DerivationAlgorithm::Ed25519, &chain);
-            let response = request.derive_with_master_seed(seed.to_vec()).unwrap();
-            assert_eq!(&response.data, private_key, "test: {chain}");
+            let response = request.derive_with_master_seed(&seed).unwrap();
+            assert_eq!(&response.data, private_key.as_slice(), "test: {chain}");
         }
     }
 }
@@ -108,7 +110,7 @@ fn panics_with_unhardened_derivation() {
     use ed25519_dalek::SigningKey;
 
     let seed = hex!("000102030405060708090a0b0c0d0e0f");
-    let xkey = ExtendedPrivateKey::<SigningKey>::new(seed).unwrap();
+    let xkey = ExtendedPrivateKey::<SigningKey>::new(seed);
     xkey.derive_path(&DerivationPath::from_str("m/0").unwrap())
         .unwrap();
 }
@@ -120,7 +122,7 @@ fn panics_at_depth() {
     use ed25519_dalek::SigningKey;
 
     let seed = hex!("000102030405060708090a0b0c0d0e0f");
-    let mut xkey = ExtendedPrivateKey::<SigningKey>::new(seed).unwrap();
+    let mut xkey = ExtendedPrivateKey::<SigningKey>::new(seed);
     for i in 0..=u32::from(u8::MAX) {
         xkey = xkey
             .derive_child(&DerivationIndex::new(i, true).unwrap())
diff --git a/crates/keyfork-shard/Cargo.toml b/crates/keyfork-shard/Cargo.toml
index f1ae88b..8c2d75a 100644
--- a/crates/keyfork-shard/Cargo.toml
+++ b/crates/keyfork-shard/Cargo.toml
@@ -7,11 +7,10 @@ license = "AGPL-3.0-only"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [features]
-default = ["openpgp", "openpgp-card", "qrcode"]
+default = ["openpgp", "openpgp-card", "qrcode", "sequoia-openpgp/crypto-nettle", "keyfork-qrcode/decode-backend-rqrr"]
 openpgp = ["sequoia-openpgp", "anyhow"]
 openpgp-card = ["openpgp-card-sequoia", "card-backend-pcsc", "card-backend", "dep:openpgp-card"]
 qrcode = ["keyfork-qrcode"]
-bin = ["sequoia-openpgp/crypto-nettle", "keyfork-qrcode/decode-backend-rqrr"]
 
 [dependencies]
 keyfork-prompt = { version = "0.1.0", path = "../util/keyfork-prompt", default-features = false, features = ["mnemonic"] }
diff --git a/crates/keyfork-shard/src/openpgp.rs b/crates/keyfork-shard/src/openpgp.rs
index 36ab011..c07396a 100644
--- a/crates/keyfork-shard/src/openpgp.rs
+++ b/crates/keyfork-shard/src/openpgp.rs
@@ -13,9 +13,9 @@ use aes_gcm::{
     Aes256Gcm, Error as AesError, KeyInit, Nonce,
 };
 use hkdf::{Hkdf, InvalidLength as HkdfInvalidLength};
-use keyfork_derive_openpgp::derive_util::{
-    request::{DerivationAlgorithm, DerivationRequest},
-    DerivationPath, PathError,
+use keyfork_derive_openpgp::{
+    derive_util::{DerivationPath, PathError, VariableLengthSeed},
+    XPrv,
 };
 use keyfork_mnemonic_util::{Mnemonic, MnemonicFromStrError, MnemonicGenerationError, Wordlist};
 use keyfork_prompt::{
@@ -123,6 +123,10 @@ pub enum Error {
     #[error("IO error: {0}")]
     Io(#[source] std::io::Error),
 
+    /// An error occurred while deriving data.
+    #[error("Derivation: {0}")]
+    Derivation(#[from] keyfork_derive_openpgp::derive_util::extended_key::private_key::Error),
+
     /// An error occurred while parsing a derivation path.
     #[error("Derivation path: {0}")]
     DerivationPath(#[from] PathError),
@@ -643,13 +647,11 @@ pub fn combine(
 
     // TODO: extract as function
     let userid = UserID::from("keyfork-sss");
-    let kdr = DerivationRequest::new(
-        DerivationAlgorithm::Ed25519,
-        &DerivationPath::from_str("m/7366512'/0'")?,
-    )
-    .derive_with_master_seed(secret.clone())?;
+    let path = DerivationPath::from_str("m/7366512'/0'")?;
+    let seed = VariableLengthSeed::new(&secret);
+    let xprv = XPrv::new(seed).derive_path(&path)?;
     let derived_cert = keyfork_derive_openpgp::derive(
-        kdr,
+        xprv,
         &[KeyFlags::empty().set_certification().set_signing()],
         &userid,
     )?;
@@ -678,15 +680,13 @@ pub fn combine(
 /// The function may panic if the metadata can't properly store the certificates used to generate
 /// the encrypted shares.
 pub fn split(threshold: u8, certs: Vec<Cert>, secret: &[u8], output: impl Write) -> Result<()> {
+    let seed = VariableLengthSeed::new(secret);
     // build cert to sign encrypted shares
     let userid = UserID::from("keyfork-sss");
-    let kdr = DerivationRequest::new(
-        DerivationAlgorithm::Ed25519,
-        &DerivationPath::from_str("m/7366512'/0'")?,
-    )
-    .derive_with_master_seed(secret.to_vec())?;
+    let path = DerivationPath::from_str("m/7366512'/0'")?;
+    let xprv = XPrv::new(seed).derive_path(&path)?;
     let derived_cert = keyfork_derive_openpgp::derive(
-        kdr,
+        xprv,
         &[KeyFlags::empty().set_certification().set_signing()],
         &userid,
     )?;
diff --git a/crates/keyfork/src/cli/derive.rs b/crates/keyfork/src/cli/derive.rs
index 7b2dc2f..27cd731 100644
--- a/crates/keyfork/src/cli/derive.rs
+++ b/crates/keyfork/src/cli/derive.rs
@@ -1,16 +1,16 @@
 use super::Keyfork;
 use clap::{Parser, Subcommand};
 
-use keyfork_derive_openpgp::openpgp::{
-    armor::{Kind, Writer},
-    packet::UserID,
-    serialize::Marshal,
-    types::KeyFlags,
-};
-use keyfork_derive_util::{
-    request::{DerivationAlgorithm, DerivationRequest, DerivationResponse},
-    DerivationIndex, DerivationPath,
+use keyfork_derive_openpgp::{
+    openpgp::{
+        armor::{Kind, Writer},
+        packet::UserID,
+        serialize::Marshal,
+        types::KeyFlags,
+    },
+    XPrvKey,
 };
+use keyfork_derive_util::{DerivationIndex, DerivationPath};
 use keyforkd_client::Client;
 
 type Result<T, E = Box<dyn std::error::Error>> = std::result::Result<T, E>;
@@ -48,12 +48,9 @@ impl DeriveSubcommands {
                         .set_storage_encryption(),
                     KeyFlags::empty().set_authentication(),
                 ];
-                let request = DerivationRequest::new(DerivationAlgorithm::Ed25519, &path);
-                let derived_data: DerivationResponse = Client::discover_socket()?
-                    .request(&request.into())?
-                    .try_into()?;
+                let xprv = Client::discover_socket()?.request_xprv::<XPrvKey>(&path)?;
                 let default_userid = UserID::from(user_id.as_str());
-                let cert = keyfork_derive_openpgp::derive(derived_data, &subkeys, &default_userid)?;
+                let cert = keyfork_derive_openpgp::derive(xprv, &subkeys, &default_userid)?;
 
                 let mut w = Writer::new(std::io::stdout(), Kind::SecretKey)?;
 
diff --git a/crates/keyfork/src/cli/wizard.rs b/crates/keyfork/src/cli/wizard.rs
index 2793890..3c6e1db 100644
--- a/crates/keyfork/src/cli/wizard.rs
+++ b/crates/keyfork/src/cli/wizard.rs
@@ -5,11 +5,11 @@ use std::{collections::HashSet, fs::File, io::IsTerminal, path::PathBuf};
 use card_backend_pcsc::PcscBackend;
 use openpgp_card_sequoia::{state::Open, types::KeyType, Card};
 
-use keyfork_derive_openpgp::openpgp::{self, packet::UserID, types::KeyFlags, Cert};
-use keyfork_derive_util::{
-    request::{DerivationAlgorithm, DerivationRequest},
-    DerivationIndex, DerivationPath,
+use keyfork_derive_openpgp::{
+    openpgp::{self, packet::UserID, types::KeyFlags, Cert},
+    XPrv,
 };
+use keyfork_derive_util::{DerivationIndex, DerivationPath};
 use keyfork_prompt::{
     validators::{PinValidator, Validator},
     Message, PromptHandler, Terminal,
@@ -21,7 +21,7 @@ pub struct PinLength(usize);
 
 type Result<T, E = Box<dyn std::error::Error>> = std::result::Result<T, E>;
 
-fn derive_key(seed: &[u8], index: u8) -> Result<Cert> {
+fn derive_key(seed: [u8; 32], index: u8) -> Result<Cert> {
     let subkeys = vec![
         KeyFlags::empty().set_certification(),
         KeyFlags::empty().set_signing(),
@@ -42,10 +42,9 @@ fn derive_key(seed: &[u8], index: u8) -> Result<Cert> {
         .chain_push(chain)
         .chain_push(account)
         .chain_push(subkey);
-    let request = DerivationRequest::new(DerivationAlgorithm::Ed25519, &path);
-    let response = request.derive_with_master_seed(seed.to_vec())?;
+    let xprv = XPrv::new(seed).derive_path(&path)?;
     let userid = UserID::from(format!("Keyfork Shard {index}"));
-    let cert = keyfork_derive_openpgp::derive(response, &subkeys, &userid)?;
+    let cert = keyfork_derive_openpgp::derive(xprv, &subkeys, &userid)?;
     Ok(cert)
 }
 
@@ -103,7 +102,7 @@ fn generate_shard_secret(
     keys_per_shard: u8,
     output_file: &Option<PathBuf>,
 ) -> Result<()> {
-    let seed = keyfork_entropy::generate_entropy_of_size(256 / 8)?;
+    let seed = keyfork_entropy::generate_entropy_of_const_size::<{256 / 8}>()?;
     let mut pm = Terminal::new(std::io::stdin(), std::io::stderr())?;
     let mut certs = vec![];
     let mut seen_cards: HashSet<String> = HashSet::new();
@@ -127,7 +126,7 @@ fn generate_shard_secret(
     .to_fn();
 
     for index in 0..max {
-        let cert = derive_key(&seed, index)?;
+        let cert = derive_key(seed, index)?;
         for i in 0..keys_per_shard {
             pm.prompt_message(Message::Text(format!(
                 "Please remove all keys and insert key #{} for user #{}",
diff --git a/crates/util/keyfork-entropy/Cargo.toml b/crates/util/keyfork-entropy/Cargo.toml
index 1d5a444..20a75c2 100644
--- a/crates/util/keyfork-entropy/Cargo.toml
+++ b/crates/util/keyfork-entropy/Cargo.toml
@@ -7,7 +7,7 @@ license = "MIT"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [features]
-default = []
+default = ["bin"]
 bin = ["smex"]
 
 [dependencies]
diff --git a/crates/util/keyfork-entropy/src/lib.rs b/crates/util/keyfork-entropy/src/lib.rs
index d7512b5..8f1580f 100644
--- a/crates/util/keyfork-entropy/src/lib.rs
+++ b/crates/util/keyfork-entropy/src/lib.rs
@@ -1,6 +1,9 @@
 //! Utilities for reading entropy from secure sources.
 
-use std::{fs::{read_dir, read_to_string, File}, io::Read};
+use std::{
+    fs::{read_dir, read_to_string, File},
+    io::Read,
+};
 
 static WARNING_LINKS: [&str; 1] =
     ["https://lore.kernel.org/lkml/20211223141113.1240679-2-Jason@zx2c4.com/"];
@@ -84,3 +87,24 @@ pub fn generate_entropy_of_size(byte_count: usize) -> Result<Vec<u8>, std::io::E
     entropy_file.read_exact(&mut vec[..])?;
     Ok(vec)
 }
+
+/// Read system entropy of a constant size.
+///
+/// # Errors
+/// An error may be returned if an error occurred while reading from the random source.
+///
+/// # Examples
+/// ```rust,no_run
+/// # fn main() -> Result<(), Box<dyn std::error::Error>> {
+/// # std::env::set_var("SHOOT_SELF_IN_FOOT", "1");
+/// let entropy = keyfork_entropy::generate_entropy_of_const_size::<64>()?;
+/// assert_eq!(entropy.len(), 64);
+/// # Ok(())
+/// # }
+/// ```
+pub fn generate_entropy_of_const_size<const N: usize>() -> Result<[u8; N], std::io::Error> {
+    let mut output = [0u8; N];
+    let mut entropy_file = File::open("/dev/urandom")?;
+    entropy_file.read_exact(&mut output[..])?;
+    Ok(output)
+}
diff --git a/crates/util/keyfork-mnemonic-util/Cargo.toml b/crates/util/keyfork-mnemonic-util/Cargo.toml
index 3707884..10c88dc 100644
--- a/crates/util/keyfork-mnemonic-util/Cargo.toml
+++ b/crates/util/keyfork-mnemonic-util/Cargo.toml
@@ -7,7 +7,7 @@ edition = "2021"
 license = "MIT"
 
 [features]
-default = []
+default = ["bin"]
 bin = ["smex"]
 
 [dependencies]
diff --git a/crates/util/keyfork-mnemonic-util/src/lib.rs b/crates/util/keyfork-mnemonic-util/src/lib.rs
index c34e305..b1eb04b 100644
--- a/crates/util/keyfork-mnemonic-util/src/lib.rs
+++ b/crates/util/keyfork-mnemonic-util/src/lib.rs
@@ -276,7 +276,7 @@ impl Mnemonic {
     }
 
     /// Clone the existing entropy.
-    #[deprecated]
+    #[deprecated = "Use as_bytes(), to_bytes(), or into_bytes() instead"]
     pub fn entropy(&self) -> Vec<u8> {
         self.entropy.clone()
     }
@@ -353,8 +353,8 @@ mod tests {
         random_handle.read_exact(&mut entropy[..]).unwrap();
         let wordlist = Wordlist::default().arc();
         let mnemonic = super::Mnemonic::from_entropy(&entropy[..256 / 8], wordlist).unwrap();
-        let new_entropy = mnemonic.entropy();
-        assert_eq!(&new_entropy, entropy);
+        let new_entropy = mnemonic.as_bytes();
+        assert_eq!(new_entropy, entropy);
     }
 
     #[test]
diff --git a/crates/util/keyfork-prompt/examples/test-basic-prompt.rs b/crates/util/keyfork-prompt/examples/test-basic-prompt.rs
index fe4ad86..801c35c 100644
--- a/crates/util/keyfork-prompt/examples/test-basic-prompt.rs
+++ b/crates/util/keyfork-prompt/examples/test-basic-prompt.rs
@@ -22,8 +22,8 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
         3,
         transport_validator.to_fn(),
     )?;
-    assert_eq!(mnemonics[0].entropy().len(), 12);
-    assert_eq!(mnemonics[1].entropy().len(), 32);
+    assert_eq!(mnemonics[0].as_bytes().len(), 12);
+    assert_eq!(mnemonics[1].as_bytes().len(), 32);
 
     let mnemonics = mgr.prompt_validated_wordlist(
         "Enter a 24 and 48-word mnemonic: ",
@@ -31,8 +31,8 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
         3,
         combine_validator.to_fn(),
     )?;
-    assert_eq!(mnemonics[0].entropy().len(), 32);
-    assert_eq!(mnemonics[1].entropy().len(), 64);
+    assert_eq!(mnemonics[0].as_bytes().len(), 32);
+    assert_eq!(mnemonics[1].as_bytes().len(), 64);
 
     Ok(())
 }