diff --git a/src/proto/extension.rs b/src/proto/extension.rs
new file mode 100644
index 0000000..76cda23
--- /dev/null
+++ b/src/proto/extension.rs
@@ -0,0 +1,28 @@
+use serde::{Deserialize, Serialize};
+
+use super::recursive;
+use super::signature::Signature;
+
+/// SSH key
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct SshKey {
+    pub alg: String,
+    pub blob: Vec<u8>,
+}
+
+/// session-bind@openssh.com extension
+///
+/// This extension allows a ssh client to bind an agent connection to a
+/// particular SSH session.
+///
+/// Spec:
+/// <https://github.com/openssh/openssh-portable/blob/cbbdf868bce431a59e2fa36ca244d5739429408d/PROTOCOL.agent#L6>
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct SessionBind {
+    #[serde(with = "recursive")]
+    pub host_key: SshKey,
+    pub session_id: Vec<u8>,
+    #[serde(with = "recursive")]
+    pub signature: Signature,
+    pub is_forwarding: bool,
+}
diff --git a/src/proto/message.rs b/src/proto/message.rs
index 044169f..9f24086 100644
--- a/src/proto/message.rs
+++ b/src/proto/message.rs
@@ -1,4 +1,5 @@
 use serde::de::{Deserializer, Visitor};
+use serde::ser::SerializeTuple;
 use serde::{Deserialize, Serialize};
 
 use super::private_key::PrivateKey;
@@ -65,7 +66,11 @@ impl Serialize for ExtensionContents {
     where
         S: serde::Serializer,
     {
-        serializer.serialize_bytes(&self.0)
+        let mut seq = serializer.serialize_tuple(self.0.len())?;
+        for i in &self.0 {
+            seq.serialize_element(i)?;
+        }
+        seq.end()
     }
 }
 
diff --git a/src/proto/mod.rs b/src/proto/mod.rs
index cade6d9..59a4663 100644
--- a/src/proto/mod.rs
+++ b/src/proto/mod.rs
@@ -4,6 +4,7 @@ pub mod ser;
 #[macro_use]
 pub mod key_type;
 pub mod error;
+pub mod extension;
 pub mod message;
 pub mod private_key;
 pub mod public_key;
@@ -40,3 +41,49 @@ impl<'a, T: Serialize + Deserialize<'a>> Blob for T {
         from_bytes(blob)
     }
 }
+
+pub mod recursive {
+    use super::{from_bytes, to_bytes};
+    use serde::{
+        de::{self, Deserializer, Visitor},
+        ser::{Error, Serializer},
+        Deserialize, Serialize,
+    };
+    use std::{fmt, marker::PhantomData};
+
+    pub fn serialize<T, S>(obj: &T, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        T: Serialize,
+        S: Serializer,
+    {
+        serializer.serialize_bytes(&to_bytes(obj).map_err(S::Error::custom)?)
+    }
+
+    pub fn deserialize<'de, T, D>(deserialize: D) -> Result<T, D::Error>
+    where
+        T: Deserialize<'de>,
+        D: Deserializer<'de>,
+    {
+        struct RecursiveVisitor<T>(PhantomData<T>);
+
+        impl<'de, T> Visitor<'de> for RecursiveVisitor<T>
+        where
+            T: Deserialize<'de>,
+        {
+            type Value = T;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                formatter.write_str("an integer between -2^31 and 2^31")
+            }
+
+            fn visit_bytes<E>(self, value: &[u8]) -> Result<Self::Value, E>
+            where
+                E: de::Error,
+            {
+                from_bytes(value).map_err(E::custom)
+            }
+        }
+
+        deserialize.deserialize_bytes(RecursiveVisitor(PhantomData::<T>))
+    }
+}
diff --git a/src/proto/ser.rs b/src/proto/ser.rs
index dbb7894..f828501 100644
--- a/src/proto/ser.rs
+++ b/src/proto/ser.rs
@@ -27,8 +27,10 @@ impl<'a, W: io::Write> ser::Serializer for &'a mut Serializer<W> {
     type SerializeStruct = Self;
     type SerializeStructVariant = Self;
 
-    fn serialize_bool(self, _v: bool) -> ProtoResult<()> {
-        unimplemented!()
+    fn serialize_bool(self, v: bool) -> ProtoResult<()> {
+        self.writer
+            .write_u8(if v { 1 } else { 0 })
+            .map_err(Into::into)
     }
 
     fn serialize_i8(self, v: i8) -> ProtoResult<()> {
@@ -76,11 +78,11 @@ impl<'a, W: io::Write> ser::Serializer for &'a mut Serializer<W> {
     }
 
     fn serialize_str(self, v: &str) -> ProtoResult<()> {
-        (v.len() as u32).serialize(&mut *self)?;
         self.serialize_bytes(v.as_bytes())
     }
 
     fn serialize_bytes(self, v: &[u8]) -> ProtoResult<()> {
+        (v.len() as u32).serialize(&mut *self)?;
         self.writer.write_all(v).map_err(Into::into)
     }
 
diff --git a/src/proto/tests/mod.rs b/src/proto/tests/mod.rs
index b83a1a5..3cdc5fa 100644
--- a/src/proto/tests/mod.rs
+++ b/src/proto/tests/mod.rs
@@ -1,3 +1,4 @@
+use super::extension::SessionBind;
 use super::message::{Extension, Identity, Message, SignRequest};
 use super::private_key::*;
 use super::public_key::*;
@@ -178,4 +179,9 @@ fn test_extension() {
     assert_eq!(extension.extension_type, "session-bind@openssh.com");
     let out = to_bytes(&extension).unwrap();
     assert_eq!(extension_bytes, out);
+
+    let session_bind: SessionBind = from_bytes(&extension.extension_contents.0).unwrap();
+
+    let out = to_bytes(&session_bind).unwrap();
+    assert_eq!(extension.extension_contents.0, out);
 }