diff --git a/Cargo.toml b/Cargo.toml
index 154cb3f..2a07a88 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -10,7 +10,7 @@ crate-type = ["cdylib"]
 [dependencies]
 paste = "1.0.15"
 thiserror = "1.0.63"
-vodozemac = "0.7.0"
+vodozemac = { git = "https://github.com/matrix-org/vodozemac.git" }
 
 [package.metadata.maturin]
 name = "vodozemac"
diff --git a/src/account.rs b/src/account.rs
index f64536c..3426eb0 100644
--- a/src/account.rs
+++ b/src/account.rs
@@ -1,9 +1,13 @@
 use std::collections::HashMap;
 
-use pyo3::{prelude::*, types::PyType};
+use pyo3::{
+    prelude::*,
+    types::{PyBytes, PyType},
+};
 use vodozemac::olm::SessionConfig;
 
 use crate::{
+    convert_to_pybytes,
     error::{LibolmPickleError, PickleError, SessionError},
     types::{Curve25519PublicKey, Ed25519PublicKey, Ed25519Signature, PreKeyMessage},
 };
@@ -70,7 +74,7 @@ impl Account {
         self.inner.curve25519_key().into()
     }
 
-    fn sign(&self, message: &str) -> Ed25519Signature {
+    fn sign(&self, message: &[u8]) -> Ed25519Signature {
         self.inner.sign(message).into()
     }
 
@@ -127,7 +131,7 @@ impl Account {
         &mut self,
         identity_key: &Curve25519PublicKey,
         message: &PreKeyMessage,
-    ) -> Result<(Session, String), SessionError> {
+    ) -> Result<(Session, Py<PyBytes>), SessionError> {
         let result = self
             .inner
             .create_inbound_session(identity_key.inner, &message.inner)?;
@@ -136,7 +140,7 @@ impl Account {
             Session {
                 inner: result.session,
             },
-            String::from_utf8(result.plaintext)?,
+            convert_to_pybytes(result.plaintext),
         ))
     }
 }
diff --git a/src/group_sessions.rs b/src/group_sessions.rs
index f4a038a..ce7390e 100644
--- a/src/group_sessions.rs
+++ b/src/group_sessions.rs
@@ -1,7 +1,11 @@
-use pyo3::{prelude::*, types::PyType};
+use pyo3::{
+    prelude::*,
+    types::{PyBytes, PyType},
+};
 use vodozemac::megolm::SessionConfig;
 
 use crate::{
+    convert_to_pybytes,
     error::{LibolmPickleError, MegolmDecryptionError, PickleError, SessionKeyDecodeError},
     types::{ExportedSessionKey, MegolmMessage, SessionKey},
 };
@@ -35,7 +39,7 @@ impl GroupSession {
         self.inner.session_key().into()
     }
 
-    fn encrypt(&mut self, plaintext: &str) -> MegolmMessage {
+    fn encrypt(&mut self, plaintext: &[u8]) -> MegolmMessage {
         self.inner.encrypt(plaintext).into()
     }
 
@@ -67,11 +71,20 @@ impl GroupSession {
 #[pyclass]
 pub struct DecryptedMessage {
     #[pyo3(get)]
-    plaintext: String,
+    plaintext: Py<PyBytes>,
     #[pyo3(get)]
     message_index: u32,
 }
 
+impl DecryptedMessage {
+    fn new(plaintext: &[u8], message_index: u32) -> Self {
+        DecryptedMessage {
+            plaintext: convert_to_pybytes(plaintext),
+            message_index,
+        }
+    }
+}
+
 #[pyclass]
 pub struct InboundGroupSession {
     pub(super) inner: vodozemac::megolm::InboundGroupSession,
@@ -122,10 +135,10 @@ impl InboundGroupSession {
     ) -> Result<DecryptedMessage, MegolmDecryptionError> {
         let ret = self.inner.decrypt(&message.inner)?;
 
-        Ok(DecryptedMessage {
-            plaintext: String::from_utf8(ret.plaintext)?,
-            message_index: ret.message_index,
-        })
+        Ok(DecryptedMessage::new(
+            ret.plaintext.as_slice(),
+            ret.message_index,
+        ))
     }
 
     fn pickle(&self, pickle_key: &[u8]) -> Result<String, PickleError> {
diff --git a/src/lib.rs b/src/lib.rs
index cff6206..662ed13 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -6,7 +6,7 @@ mod session;
 mod types;
 
 use error::*;
-use pyo3::prelude::*;
+use pyo3::{prelude::*, types::PyBytes};
 
 #[pymodule(name = "vodozemac")]
 fn my_module(py: Python<'_>, m: &Bound<'_, PyModule>) -> PyResult<()> {
@@ -58,3 +58,7 @@ fn my_module(py: Python<'_>, m: &Bound<'_, PyModule>) -> PyResult<()> {
 
     Ok(())
 }
+
+pub(crate) fn convert_to_pybytes(bytes: impl AsRef<[u8]>) -> Py<PyBytes> {
+    Python::with_gil(|py| PyBytes::new_bound(py, bytes.as_ref()).into())
+}
diff --git a/src/session.rs b/src/session.rs
index 98100b1..02ff978 100644
--- a/src/session.rs
+++ b/src/session.rs
@@ -1,6 +1,10 @@
-use pyo3::{prelude::*, types::PyType};
+use pyo3::{
+    prelude::*,
+    types::{PyBytes, PyType},
+};
 
 use crate::{
+    convert_to_pybytes,
     types::{AnyOlmMessage, PreKeyMessage},
     LibolmPickleError, PickleError, SessionError,
 };
@@ -56,12 +60,12 @@ impl Session {
         Ok(Self { inner: session })
     }
 
-    fn encrypt(&mut self, plaintext: &str) -> AnyOlmMessage {
+    fn encrypt(&mut self, plaintext: &[u8]) -> AnyOlmMessage {
         let message = self.inner.encrypt(plaintext);
         AnyOlmMessage { inner: message }
     }
 
-    fn decrypt(&mut self, message: &AnyOlmMessage) -> Result<String, SessionError> {
-        Ok(String::from_utf8(self.inner.decrypt(&message.inner)?)?)
+    fn decrypt(&mut self, message: &AnyOlmMessage) -> Result<Py<PyBytes>, SessionError> {
+        Ok(convert_to_pybytes(self.inner.decrypt(&message.inner)?))
     }
 }
diff --git a/src/types/ed25519.rs b/src/types/ed25519.rs
index 13a9ad2..e0553eb 100644
--- a/src/types/ed25519.rs
+++ b/src/types/ed25519.rs
@@ -21,10 +21,10 @@ impl Ed25519PublicKey {
 
     pub fn verify_signature(
         &self,
-        message: &str,
+        message: &[u8],
         signature: &Ed25519Signature,
     ) -> Result<(), SignatureError> {
-        self.inner.verify(message.as_bytes(), &signature.inner)?;
+        self.inner.verify(message, &signature.inner)?;
 
         Ok(())
     }
diff --git a/src/types/messages.rs b/src/types/messages.rs
index 410232a..ea9f6d5 100644
--- a/src/types/messages.rs
+++ b/src/types/messages.rs
@@ -1,5 +1,8 @@
-use crate::error::*;
-use pyo3::{prelude::*, types::PyType};
+use crate::{convert_to_pybytes, error::*};
+use pyo3::{
+    prelude::*,
+    types::{PyBytes, PyType},
+};
 
 #[pyclass]
 pub struct AnyOlmMessage {
@@ -9,16 +12,16 @@ pub struct AnyOlmMessage {
 #[pymethods]
 impl AnyOlmMessage {
     #[classmethod]
-    pub fn pre_key(_cls: &Bound<'_, PyType>, message: &str) -> Result<Self, SessionError> {
+    pub fn pre_key(_cls: &Bound<'_, PyType>, message: &[u8]) -> Result<Self, SessionError> {
         Ok(Self {
-            inner: vodozemac::olm::PreKeyMessage::from_base64(message)?.into(),
+            inner: vodozemac::olm::PreKeyMessage::from_bytes(message)?.into(),
         })
     }
 
     #[classmethod]
-    pub fn normal(_cls: &Bound<'_, PyType>, message: &str) -> Result<Self, SessionError> {
+    pub fn normal(_cls: &Bound<'_, PyType>, message: &[u8]) -> Result<Self, SessionError> {
         Ok(Self {
-            inner: vodozemac::olm::Message::from_base64(message)?.into(),
+            inner: vodozemac::olm::Message::from_bytes(message)?.into(),
         })
     }
 
@@ -36,15 +39,16 @@ impl AnyOlmMessage {
     pub fn from_parts(
         _cls: &Bound<'_, PyType>,
         message_type: usize,
-        ciphertext: &str,
+        ciphertext: &[u8],
     ) -> Result<Self, DecodeError> {
         Ok(Self {
             inner: vodozemac::olm::OlmMessage::from_parts(message_type, ciphertext)?,
         })
     }
 
-    pub fn to_parts(&self) -> (usize, String) {
-        self.inner.clone().to_parts()
+    pub fn to_parts(&self) -> (usize, Py<PyBytes>) {
+        let (message_type, ciphertext) = self.inner.clone().to_parts();
+        (message_type, convert_to_pybytes(ciphertext))
     }
 }
 
diff --git a/tests/account_test.py b/tests/account_test.py
index 976c482..4e9b177 100644
--- a/tests/account_test.py
+++ b/tests/account_test.py
@@ -57,8 +57,8 @@ def test_publish_one_time_keys(self):
 
     def test_signing(self):
         alice = Account()
-        signature = alice.sign("This is a test")
+        signature = alice.sign(b"This is a test")
 
-        alice.ed25519_key.verify_signature("This is a test", signature)
+        alice.ed25519_key.verify_signature(b"This is a test", signature)
         with pytest.raises(SignatureException):
-            alice.ed25519_key.verify_signature("This should fail", signature)
+            alice.ed25519_key.verify_signature(b"This should fail", signature)
diff --git a/tests/group_session_test.py b/tests/group_session_test.py
index 7fcd102..5fe160b 100644
--- a/tests/group_session_test.py
+++ b/tests/group_session_test.py
@@ -54,8 +54,8 @@ def test_inbound_export(self):
         imported = InboundGroupSession.import_session(
             inbound.export_at(inbound.first_known_index)
         )
-        message = imported.decrypt(outbound.encrypt("Test"))
-        assert message.plaintext == "Test"
+        message = imported.decrypt(outbound.encrypt(b"Test"))
+        assert message.plaintext == b"Test"
         assert message.message_index == 0
 
     def test_first_index(self):
@@ -68,24 +68,24 @@ def test_first_index(self):
     def test_encrypt(self):
         outbound = GroupSession()
         inbound = InboundGroupSession(outbound.session_key)
-        message = inbound.decrypt(outbound.encrypt("Test"))
-        assert "Test", 0 == inbound.decrypt(outbound.encrypt("Test"))
+        message = inbound.decrypt(outbound.encrypt(b"Test"))
+        assert b"Test", 0 == inbound.decrypt(outbound.encrypt(b"Test"))
 
     def test_decrypt_twice(self):
         outbound = GroupSession()
         inbound = InboundGroupSession(outbound.session_key)
-        outbound.encrypt("Test 1")
-        message = inbound.decrypt(outbound.encrypt("Test 2"))
+        outbound.encrypt(b"Test 1")
+        message = inbound.decrypt(outbound.encrypt(b"Test 2"))
         assert isinstance(message.message_index, int)
         assert message.message_index == 1
-        assert message.plaintext == "Test 2"
+        assert message.plaintext == b"Test 2"
 
     def test_decrypt_failure(self):
         outbound = GroupSession()
         inbound = InboundGroupSession(outbound.session_key)
         eve_outbound = GroupSession()
         with pytest.raises(MegolmDecryptionException):
-            inbound.decrypt(eve_outbound.encrypt("Test"))
+            inbound.decrypt(eve_outbound.encrypt(b"Test"))
 
     def test_id(self):
         outbound = GroupSession()
diff --git a/tests/session_test.py b/tests/session_test.py
index 247e1e8..a31479c 100644
--- a/tests/session_test.py
+++ b/tests/session_test.py
@@ -55,7 +55,7 @@ def test_wrong_passphrase_pickle(self):
             Session.from_pickle(pickle, PICKLE_KEY)
 
     def test_encrypt(self):
-        plaintext = "It's a secret to everybody"
+        plaintext = b"It's a secret to everybody"
         alice, bob, session = self._create_session()
         message = session.encrypt(plaintext)
 
@@ -69,10 +69,10 @@ def test_encrypt(self):
 
     def test_empty_message(self):
         with pytest.raises(DecodeException):
-            AnyOlmMessage.from_parts(0, "x")
+            AnyOlmMessage.from_parts(0, b"x")
 
     def test_two_messages(self):
-        plaintext = "It's a secret to everybody"
+        plaintext = b"It's a secret to everybody"
         alice, bob, session = self._create_session()
         message = session.encrypt(plaintext)
         message = message.to_pre_key()
@@ -82,13 +82,13 @@ def test_two_messages(self):
         )
         assert plaintext == decrypted
 
-        bob_plaintext = "Grumble, Grumble"
+        bob_plaintext = b"Grumble, Grumble"
         bob_message = bob_session.encrypt(bob_plaintext)
 
         assert bob_plaintext == session.decrypt(bob_message)
 
     def test_matches(self):
-        plaintext = "It's a secret to everybody"
+        plaintext = b"It's a secret to everybody"
         alice, bob, session = self._create_session()
         message = session.encrypt(plaintext)
         message = message.to_pre_key()
@@ -98,7 +98,7 @@ def test_matches(self):
         )
         assert plaintext == decrypted
 
-        message2 = session.encrypt("Hey! Listen!")
+        message2 = session.encrypt(b"Hey! Listen!")
         message2 = message2.to_pre_key()
 
         assert bob_session.session_matches(message2) is True
@@ -107,13 +107,13 @@ def test_invalid(self):
         alice, bob, session = self._create_session()
         _, _, another_session = self._create_session()
 
-        message = another_session.encrypt("It's a secret to everybody")
+        message = another_session.encrypt(b"It's a secret to everybody")
         message = message.to_pre_key()
 
         assert not session.session_matches(message)
 
     def test_does_not_match(self):
-        plaintext = "It's a secret to everybody"
+        plaintext = b"It's a secret to everybody"
         alice, bob, session = self._create_session()
         message = session.encrypt(plaintext)
         message = message.to_pre_key()
@@ -129,7 +129,7 @@ def test_does_not_match(self):
         assert bob_session.session_matches(new_message) is False
 
     def test_message_to_parts(self):
-        plaintext = "It's a secret to everybody"
+        plaintext = b"It's a secret to everybody"
         alice, bob, session = self._create_session()
         message = session.encrypt(plaintext)