commit 0bbcab572744f8c0fccc66070acd184373cc00f8
Author: Alex Emmet <111742636+Alex-Emmet@users.noreply.github.com>
Date:   Sat Jun 20 01:55:31 2026 +0200

    Initial commit

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..4c1b18f
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+**target/
+**Cargo.lock
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..78c22f3
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,12 @@
+[workspace]
+members = [
+    "common",
+    "crypto",
+    "registry",
+    "type-map",
+    "codec",
+    "transport",
+    "host",
+    "client",
+]
+resolver = "3"
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..4cb4408
--- /dev/null
+++ b/README.md
@@ -0,0 +1,60 @@
+# **M**ethanium **T**ransport **P**rotocol
+
+**MTP** is a **m**odular **t**ransport **p**rotocol by Methanium.
+
+## Crates
+- Common
+- Crypto
+- TypeMap
+- Registry
+- Codec
+- Transport
+- Host
+- Client
+
+## Registry & TypeMaps
+A TypeMap maps Communication-Types to a byte, and Data-Types to 2 bytes.
+A Communication- or Data-Type is a String to be used Plain in the code, while the Byte is transmitted.
+
+The Registries map a TypeMap to a specific version of MTP.
+
+## Codec
+The Codec crate handles encoding and decoding of MTP packets using Communication Types and Data Types from the Registry.
+The Codec has these Data Values:
+- Container
+- Encrypted Container
+- Signed Integer
+- Unsigned Integer
+- Boolean 
+- Signed Float
+- String
+- Array
+- Binary (List of Bytes)
+
+The Codec uses the Crypto crate to encrypt and decrypt Encrypted Containers.
+
+## Transport
+The Transport crate wraps QUIC.
+
+## Host & Client
+The host creates a quic Server that listens for incoming connections.
+The host also manages the registry and versions to allow for backwards compatibility with clients.
+
+The client connects to a quic Server and uses a registry to communicate with the host.
+
+The Client may be Outdated while the Host is updated.
+
+## Common
+Common Handles Logging and Error Handling. Personal information reported to Common will be anonmized.
+
+## Crypto Stack
+| Crate            | Audited? | Notes                                            |
+| ---------------- | -------- | ------------------------------------------------ |
+| ml-dsa           | No       | NIST vectors pass; regression bug fixed Jan 2026 |
+| ed25519-dalek    | Yes      | Used by Signal, Diem                             |
+| chacha20poly1305 | Yes      | NCC Group audit, Dec 2019                        |
+| aes-gcm          | Yes      | NCC Group audit, Dec 2019                        |
+| hkdf             | No       | Simple construction; well-reviewed               |
+| sha2             | No       | Standard construction; widely reviewed           |
+| zeroize          | No       | Simple; widely used                              |
+| mlkem-tls        | No       | mlkem-rs backend unaudited                       |
diff --git a/client/Cargo.toml b/client/Cargo.toml
new file mode 100644
index 0000000..09c50c3
--- /dev/null
+++ b/client/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "client"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
diff --git a/client/src/lib.rs b/client/src/lib.rs
new file mode 100644
index 0000000..b93cf3f
--- /dev/null
+++ b/client/src/lib.rs
@@ -0,0 +1,14 @@
+pub fn add(left: u64, right: u64) -> u64 {
+    left + right
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn it_works() {
+        let result = add(2, 2);
+        assert_eq!(result, 4);
+    }
+}
diff --git a/codec/Cargo.toml b/codec/Cargo.toml
new file mode 100644
index 0000000..652fbe6
--- /dev/null
+++ b/codec/Cargo.toml
@@ -0,0 +1,19 @@
+[package]
+name = "mtp-codec"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+type-map = { path = "../type-map" }
+common = { path = "../common" }
+mtp-crypto = { path = "../crypto", optional = true }
+base64 = "*"
+byteorder = "*"
+rand = { version = "*", features = ["std", "std_rng"] }
+
+[features]
+default = []
+# Enables the Registry module and versioned codec wrapper
+registry = []
+# Enables EncryptedContainer support via mtp-crypto
+crypto = ["dep:mtp-crypto"]
diff --git a/codec/src/communication_types.rs b/codec/src/communication_types.rs
new file mode 100644
index 0000000..16a4f1d
--- /dev/null
+++ b/codec/src/communication_types.rs
@@ -0,0 +1,25 @@
+// Communication types used in the MTP protocol.
+// The numeric values are part of the on‑wire format.
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[allow(non_camel_case_types)]
+pub enum CommunicationType {
+    ping = 0x01,
+    message_send = 0x02,
+    update = 0x03,
+}
+
+impl CommunicationType {
+    pub fn as_number(self) -> u8 {
+        self as u8
+    }
+
+    pub fn from_number(n: u8) -> Self {
+        match n {
+            0x01 => CommunicationType::ping,
+            0x02 => CommunicationType::message_send,
+            0x03 => CommunicationType::update,
+            _ => CommunicationType::ping,
+        }
+    }
+}
diff --git a/codec/src/communication_value.rs b/codec/src/communication_value.rs
new file mode 100644
index 0000000..354efc2
--- /dev/null
+++ b/codec/src/communication_value.rs
@@ -0,0 +1,300 @@
+use byteorder::{BigEndian, ReadBytesExt, WriteBytesExt};
+use std::collections::BTreeMap;
+use std::io::{Cursor, Read};
+
+use crate::data_value::DataValue;
+use crate::rand_u32;
+use type_map::{CommTypeId, DataTypeId};
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct CommunicationValue {
+    id: u32,
+    comm_type: CommTypeId,
+    sender: u64,
+    receiver: u64,
+    data: BTreeMap<DataTypeId, DataValue>,
+}
+
+#[allow(dead_code)]
+impl CommunicationValue {
+    pub fn new(comm_type: CommTypeId) -> Self {
+        Self {
+            id: rand_u32(),
+            comm_type,
+            sender: 0,
+            receiver: 0,
+            data: BTreeMap::new(),
+        }
+    }
+
+    pub fn with_id(mut self, p0: u32) -> Self {
+        self.id = p0;
+        self
+    }
+
+    pub fn get_id(&self) -> u32 {
+        self.id
+    }
+
+    pub fn with_sender(mut self, sender: u64) -> Self {
+        self.sender = sender;
+        self
+    }
+
+    pub fn get_sender(&self) -> u64 {
+        self.sender
+    }
+
+    pub fn with_receiver(mut self, receiver: u64) -> Self {
+        self.receiver = receiver;
+        self
+    }
+
+    pub fn get_receiver(&self) -> u64 {
+        self.receiver
+    }
+
+    pub fn get_type(&self) -> CommTypeId {
+        self.comm_type
+    }
+
+    pub fn is_type(&self, p0: CommTypeId) -> bool {
+        self.comm_type == p0
+    }
+
+    pub fn add_data(mut self, data: DataTypeId, value: DataValue) -> Self {
+        self.data.insert(data, value);
+        self
+    }
+
+    pub fn get_data(&self, data_type: DataTypeId) -> &DataValue {
+        self.data.get(&data_type).unwrap_or(&DataValue::Null)
+    }
+
+    pub fn get_data_container(&self) -> &BTreeMap<DataTypeId, DataValue> {
+        &self.data
+    }
+}
+
+impl CommunicationValue {
+    /*
+     * Frame format (strict new format):
+     * [4 bytes u32 total_length] // number of bytes after this field
+     * [1 byte communication_type]
+     * [1 byte flags]
+     * [optional 4 bytes id]      // if flags bit2 set
+     * [optional 6 bytes sender]  // if flags bit0 set
+     * [optional 6 bytes receiver]// if flags bit1 set
+     * [data container bytes...]
+     *
+     * Flags:
+     * bit0 => has sender
+     * bit1 => has receiver
+     * bit2 => has id
+     */
+    pub fn to_bytes(&self) -> Vec<u8> {
+        let mut payload = Vec::new();
+
+        let has_sender = self.sender != 0;
+        let has_receiver = self.receiver != 0;
+        let has_id = self.id != 0;
+
+        let mut flags: u8 = 0;
+        if has_sender {
+            flags |= 0b0000_0001;
+        }
+        if has_receiver {
+            flags |= 0b0000_0010;
+        }
+        if has_id {
+            flags |= 0b0000_0100;
+        }
+
+        payload.push(self.comm_type.0);
+        payload.push(flags);
+
+        if has_id {
+            let _ = payload.write_u32::<BigEndian>(self.id);
+        }
+
+        if has_sender {
+            let sender_be = self.sender.to_be_bytes();
+            payload.extend_from_slice(&sender_be[2..]); // 6 bytes
+        }
+
+        if has_receiver {
+            let receiver_be = self.receiver.to_be_bytes();
+            payload.extend_from_slice(&receiver_be[2..]); // 6 bytes
+        }
+
+        let container_value = DataValue::container_from_map(&self.data);
+        let container_bytes = container_value.to_bytes();
+        payload.extend_from_slice(&container_bytes);
+
+        let mut frame = Vec::with_capacity(4 + payload.len());
+        let _ = frame.write_u32::<BigEndian>(payload.len() as u32);
+        frame.extend_from_slice(&payload);
+
+        frame
+    }
+
+    pub fn from_bytes(bytes: &[u8]) -> Option<Self> {
+        let mut cursor = Cursor::new(bytes);
+
+        let total_len = cursor.read_u32::<BigEndian>().ok()? as usize;
+        if bytes.len() < 4 + total_len {
+            return None;
+        }
+
+        let frame_end = 4 + total_len;
+
+        let comm_type_num = cursor.read_u8().ok()?;
+        let comm_type = CommTypeId(comm_type_num);
+
+        let flags = cursor.read_u8().ok()?;
+        let has_sender = (flags & 0b0000_0001) != 0;
+        let has_receiver = (flags & 0b0000_0010) != 0;
+        let has_id = (flags & 0b0000_0100) != 0;
+
+        let id = if has_id {
+            cursor.read_u32::<BigEndian>().ok()?
+        } else {
+            0
+        };
+
+        let sender = if has_sender {
+            let mut buf = [0u8; 8];
+            cursor.read_exact(&mut buf[2..]).ok()?;
+            u64::from_be_bytes(buf)
+        } else {
+            0
+        };
+
+        let receiver = if has_receiver {
+            let mut buf = [0u8; 8];
+            cursor.read_exact(&mut buf[2..]).ok()?;
+            u64::from_be_bytes(buf)
+        } else {
+            0
+        };
+
+        let pos = cursor.position() as usize;
+        if pos > frame_end {
+            return None;
+        }
+
+        let data_bytes = &bytes[pos..frame_end];
+        let data_value = DataValue::from_bytes(data_bytes)?;
+        let data = data_value.as_map()?;
+
+        Some(Self {
+            id,
+            comm_type,
+            sender,
+            receiver,
+            data,
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::data_value::DataValue;
+    use type_map::{CommTypeId, DataTypeId};
+
+    fn roundtrip(cv: CommunicationValue) -> CommunicationValue {
+        let bytes = cv.to_bytes();
+        let decoded = CommunicationValue::from_bytes(&bytes).expect("failed to deserialize");
+        let bytes2 = decoded.to_bytes();
+        assert_eq!(bytes, bytes2);
+        decoded
+    }
+
+    #[test]
+    fn test_flags_and_order_without_optional() {
+        let cv = CommunicationValue::new(CommTypeId(1)).with_id(0);
+        let bytes = cv.to_bytes();
+
+        // [u32 len][type][flags]...
+        assert!(bytes.len() >= 6);
+        let mut c = Cursor::new(bytes.as_slice());
+        let total_len = c.read_u32::<BigEndian>().expect("read len");
+        assert_eq!(total_len as usize + 4, bytes.len());
+
+        let typ = c.read_u8().expect("read type");
+        assert_eq!(typ, 1);
+
+        let flags = c.read_u8().expect("read flags");
+        assert_eq!(flags & 0b0000_0111, 0);
+    }
+
+    #[test]
+    fn test_flags_and_order_with_all_optional() {
+        let cv = CommunicationValue::new(CommTypeId(2))
+            .with_id(0xAABBCCDD)
+            .with_sender(0x0000_1122_3344_5566)
+            .with_receiver(0x0000_6677_8899_AABB);
+
+        let bytes = cv.to_bytes();
+        let mut c = Cursor::new(bytes.as_slice());
+
+        let total_len = c.read_u32::<BigEndian>().expect("len");
+        assert_eq!(total_len as usize + 4, bytes.len());
+
+        let typ = c.read_u8().expect("type");
+        assert_eq!(typ, 2);
+
+        let flags = c.read_u8().expect("flags");
+        assert_eq!(flags & 0b0000_0111, 0b0000_0111);
+
+        let id = c.read_u32::<BigEndian>().expect("id");
+        assert_eq!(id, 0xAABBCCDD);
+
+        let mut sender6 = [0u8; 6];
+        c.read_exact(&mut sender6).expect("sender");
+        assert_eq!(sender6, [0x11, 0x22, 0x33, 0x44, 0x55, 0x66]);
+
+        let mut receiver6 = [0u8; 6];
+        c.read_exact(&mut receiver6).expect("receiver");
+        assert_eq!(receiver6, [0x66, 0x77, 0x88, 0x99, 0xAA, 0xBB]);
+    }
+
+    #[test]
+    fn test_roundtrip_complex() {
+        let cv = CommunicationValue::new(CommTypeId(3))
+            .with_id(1234)
+            .with_sender(111)
+            .with_receiver(222)
+            .add_data(DataTypeId(1), DataValue::Str("alice".to_string()))
+            .add_data(DataTypeId(2), DataValue::SignedNumber(42))
+            .add_data(DataTypeId(3), DataValue::BoolTrue)
+            .add_data(
+                DataTypeId(4),
+                DataValue::Array(vec![DataValue::SignedNumber(1), DataValue::SignedNumber(2)]),
+            );
+
+        let decoded = roundtrip(cv.clone());
+
+        assert_eq!(decoded.get_id(), 1234);
+        assert_eq!(decoded.get_sender(), 111);
+        assert_eq!(decoded.get_receiver(), 222);
+        assert_eq!(decoded.get_type(), CommTypeId(3));
+        assert_eq!(
+            decoded.get_data(DataTypeId(1)),
+            &DataValue::Str("alice".to_string())
+        );
+        assert_eq!(
+            decoded.get_data(DataTypeId(2)),
+            &DataValue::SignedNumber(42)
+        );
+    }
+
+    #[test]
+    fn test_corrupted_length_returns_none() {
+        let mut bad = vec![0u8; 8];
+        // total_length claims more than available
+        bad[0..4].copy_from_slice(&(1000u32.to_be_bytes()));
+        assert!(CommunicationValue::from_bytes(&bad).is_none());
+    }
+}
diff --git a/codec/src/data_value.rs b/codec/src/data_value.rs
new file mode 100644
index 0000000..f283dd2
--- /dev/null
+++ b/codec/src/data_value.rs
@@ -0,0 +1,663 @@
+use base64::Engine;
+use base64::engine::general_purpose;
+use byteorder::{BigEndian, ReadBytesExt, WriteBytesExt};
+use std::collections::BTreeMap;
+use std::hash::{Hash, Hasher};
+use std::io::Cursor;
+
+use type_map::DataTypeId;
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum DataKind {
+    Bool,
+
+    SignedNumber,
+    UnsignedNumber,
+    Float,
+
+    Str,
+    Bytes,
+    Array(Box<DataKind>),
+
+    Container,
+
+    #[cfg(feature = "crypto")]
+    EncryptedContainer,
+
+    Null,
+}
+
+#[derive(Debug, Clone, Eq)]
+pub enum DataValue {
+    BoolTrue,
+    BoolFalse,
+    Bool(bool),
+
+    SignedNumber(i128),
+    UnsignedNumber(u128),
+    Float(u8, u32),
+
+    Str(String),
+    Bytes(Vec<u8>),
+    Array(Vec<DataValue>),
+
+    Container(Vec<(DataTypeId, DataValue)>),
+
+    #[cfg(feature = "crypto")]
+    EncryptedContainer(Vec<(DataTypeId, DataValue)>),
+
+    Null,
+}
+
+impl DataValue {
+    /*
+     * Container format:
+     * [2 bytes u16 entry_count]       // number of key-value pairs
+     * [1 byte kind]                   // DataValue kind marker
+     * [if kind == BOOL_TRUE or BOOL_FALSE:]
+     *     [1 byte key]                // DataTypes discriminant
+     * [else:]
+     *     [2 bytes u16 payload_len]   // length of the value payload
+     *     [1 byte key]                // DataTypes discriminant
+     *     [payload_len bytes payload] // value data (interpreted based on kind)
+     *
+     * Kind markers:
+     * 0x01 => BoolTrue
+     * 0x02 => BoolFalse
+     * 0x03 => Number (i64, 8 bytes big-endian)
+     * 0x04 => Str (UTF-8 bytes)
+     * 0x05 => Array (nested container format)
+     * 0x06 => Container (nested container format)
+     * 0x07 => Null
+     */
+    const KIND_BOOL_TRUE: u8 = 0x01;
+    const KIND_BOOL_FALSE: u8 = 0x02;
+
+    const KIND_SIGNED_NUMBER: u8 = 0x03;
+    const KIND_UNSIGNED_NUMBER: u8 = 0x04;
+    const KIND_FLOAT: u8 = 0x05;
+
+    const KIND_STR: u8 = 0x06;
+    const KIND_BYTES: u8 = 0x07;
+    const KIND_ARRAY: u8 = 0x08;
+
+    const KIND_CONTAINER: u8 = 0x09;
+    #[cfg(feature = "crypto")]
+    const KIND_ENCRYPTED_CONTAINER: u8 = 0x0A;
+
+    const KIND_NULL: u8 = 0x0B;
+
+    pub fn container_from_map(map: &BTreeMap<DataTypeId, DataValue>) -> DataValue {
+        let mut container = Vec::new();
+        for (key, value) in map {
+            container.push((key.clone(), value.clone()));
+        }
+        DataValue::Container(container)
+    }
+
+    pub fn kind(&self) -> DataKind {
+        match self {
+            DataValue::Bool(_) | DataValue::BoolTrue | DataValue::BoolFalse => DataKind::Bool,
+            DataValue::SignedNumber(_) => DataKind::SignedNumber,
+            DataValue::UnsignedNumber(_) => DataKind::UnsignedNumber,
+            DataValue::Float(_, _) => DataKind::Float,
+            DataValue::Str(_) => DataKind::Str,
+            DataValue::Array(a) => {
+                if let Some(first) = a.first() {
+                    DataKind::Array(Box::new(first.kind()))
+                } else {
+                    DataKind::Array(Box::new(DataKind::Null))
+                }
+            }
+            DataValue::Bytes(_) => DataKind::Bytes,
+            DataValue::Container(_) => DataKind::Container,
+            #[cfg(feature = "crypto")]
+            DataValue::EncryptedContainer(_) => DataKind::EncryptedContainer,
+            DataValue::Null => DataKind::Null,
+        }
+    }
+
+    pub fn as_bool(&self) -> Option<bool> {
+        match self {
+            DataValue::BoolTrue => Some(true),
+            DataValue::BoolFalse => Some(false),
+            DataValue::Bool(v) => Some(*v),
+            _ => None,
+        }
+    }
+
+    pub fn as_str(&self) -> Option<&str> {
+        match self {
+            DataValue::Str(s) => Some(s),
+            _ => None,
+        }
+    }
+
+    pub fn as_string(&self) -> Option<String> {
+        self.as_str().map(|s| s.to_string())
+    }
+
+    pub fn as_signed_number(&self) -> Option<i128> {
+        match self {
+            DataValue::SignedNumber(n) => Some(*n),
+            _ => None,
+        }
+    }
+
+    pub fn as_unsigned_number(&self) -> Option<u128> {
+        match self {
+            DataValue::UnsignedNumber(n) => Some(*n),
+            _ => None,
+        }
+    }
+
+    pub fn as_float(&self) -> Option<(u8, u32)> {
+        match self {
+            DataValue::Float(a, b) => Some((*a, *b)),
+            _ => None,
+        }
+    }
+
+    pub fn as_array(&self) -> Option<Vec<DataValue>> {
+        match self {
+            DataValue::Array(a) => Some(a.clone()),
+            _ => None,
+        }
+    }
+
+    pub fn as_bytes(&self) -> Option<Vec<u8>> {
+        match self {
+            DataValue::Bytes(b) => Some(b.clone()),
+            _ => None,
+        }
+    }
+
+    pub fn as_container(&self) -> Option<Vec<(DataTypeId, DataValue)>> {
+        match self {
+            DataValue::Container(c) => Some(c.clone()),
+            _ => None,
+        }
+    }
+
+    #[cfg(feature = "crypto")]
+    pub fn as_encrypted_container(&self) -> Option<Vec<(DataTypeId, DataValue)>> {
+        match self {
+            DataValue::EncryptedContainer(c) => Some(c.clone()),
+            _ => None,
+        }
+    }
+
+    pub fn as_map(&self) -> Option<BTreeMap<DataTypeId, DataValue>> {
+        match self {
+            DataValue::Container(c) => {
+                let mut out = BTreeMap::new();
+                for (k, v) in c {
+                    out.insert(k.clone(), v.clone());
+                }
+                Some(out)
+            }
+            _ => None,
+        }
+    }
+
+    pub fn to_bytes(&self) -> Vec<u8> {
+        match self {
+            DataValue::Container(entries) => Self::encode_container(entries),
+            DataValue::Array(arr) => Self::encode_array(arr),
+            _ => {
+                let mut out = Vec::new();
+                if Self::write_value_payload(&mut out, self).is_none() {
+                    return Vec::new();
+                }
+                out
+            }
+        }
+    }
+
+    pub fn from_bytes(bytes: &[u8]) -> Option<Self> {
+        let mut cursor = Cursor::new(bytes);
+        let value = Self::read_value(&mut cursor, true)?;
+        if cursor.position() as usize != bytes.len() {
+            return None;
+        }
+        Some(value)
+    }
+
+    pub fn to_base64(&self) -> String {
+        general_purpose::STANDARD.encode(self.to_bytes())
+    }
+
+    pub fn from_base64(base64_str: &str) -> Option<Self> {
+        let bytes = general_purpose::STANDARD.decode(base64_str).ok()?;
+        Self::from_bytes(&bytes)
+    }
+
+    fn encode_container(entries: &[(DataTypeId, DataValue)]) -> Vec<u8> {
+        let mut out = Vec::new();
+        if out
+            .write_u16::<BigEndian>(u16::try_from(entries.len()).ok().unwrap_or(0))
+            .is_err()
+        {
+            return Vec::new();
+        }
+
+        for (key, value) in entries {
+            if !Self::write_container_entry(&mut out, key.clone(), value) {
+                return Vec::new();
+            }
+        }
+        out
+    }
+
+    fn write_container_entry(buf: &mut Vec<u8>, key: DataTypeId, value: &DataValue) -> bool {
+        let kind = Self::kind_marker(value);
+        buf.push(kind);
+
+        if kind == Self::KIND_BOOL_TRUE || kind == Self::KIND_BOOL_FALSE {
+            let key = u8::try_from(key.0).unwrap_or(0);
+            buf.push(key);
+            return true;
+        }
+
+        let mut payload = Vec::new();
+        if Self::write_value_payload(&mut payload, value).is_none() {
+            return false;
+        }
+
+        let len_u16 = match u16::try_from(payload.len()) {
+            Ok(v) => v,
+            Err(_) => return false,
+        };
+
+        if buf.write_u16::<BigEndian>(len_u16).is_err() {
+            return false;
+        }
+        let key = u8::try_from(key.0).unwrap_or(0);
+        buf.push(key);
+        buf.extend_from_slice(&payload);
+        true
+    }
+
+    fn encode_array(arr: &[DataValue]) -> Vec<u8> {
+        let mut out = Vec::new();
+        if out
+            .write_u16::<BigEndian>(u16::try_from(arr.len()).ok().unwrap_or(0))
+            .is_err()
+        {
+            return Vec::new();
+        }
+
+        for value in arr {
+            if !Self::write_array_entry(&mut out, value) {
+                return Vec::new();
+            }
+        }
+
+        out
+    }
+
+    fn write_array_entry(buf: &mut Vec<u8>, value: &DataValue) -> bool {
+        let kind = Self::kind_marker(value);
+        buf.push(kind);
+
+        if kind == Self::KIND_BOOL_TRUE || kind == Self::KIND_BOOL_FALSE {
+            return true;
+        }
+
+        let mut payload = Vec::new();
+        if Self::write_value_payload(&mut payload, value).is_none() {
+            return false;
+        }
+
+        let len_u16 = match u16::try_from(payload.len()) {
+            Ok(v) => v,
+            Err(_) => return false,
+        };
+
+        if buf.write_u16::<BigEndian>(len_u16).is_err() {
+            return false;
+        }
+        buf.extend_from_slice(&payload);
+        true
+    }
+
+    fn write_value_payload(buf: &mut Vec<u8>, value: &DataValue) -> Option<()> {
+        match value {
+            DataValue::BoolTrue => Some(()),
+            DataValue::BoolFalse => Some(()),
+            DataValue::Bool(v) => {
+                if *v {
+                    Some(())
+                } else {
+                    Some(())
+                }
+            }
+            DataValue::SignedNumber(n) => {
+                buf.write_i128::<BigEndian>(*n).ok()?;
+                Some(())
+            }
+            DataValue::UnsignedNumber(n) => {
+                buf.write_u128::<BigEndian>(*n).ok()?;
+                Some(())
+            }
+            DataValue::Float(a, b) => {
+                buf.write_u8(*a).ok()?;
+                buf.write_u32::<BigEndian>(*b).ok()?;
+                Some(())
+            }
+            DataValue::Str(s) => {
+                buf.extend_from_slice(s.as_bytes());
+                Some(())
+            }
+            DataValue::Array(arr) => {
+                let bytes = Self::encode_array(arr);
+                buf.extend_from_slice(&bytes);
+                Some(())
+            }
+            DataValue::Bytes(b) => {
+                buf.extend_from_slice(b);
+                Some(())
+            }
+            DataValue::Container(entries) => {
+                let bytes = Self::encode_container(entries);
+                buf.extend_from_slice(&bytes);
+                Some(())
+            }
+            #[cfg(feature = "crypto")]
+            DataValue::EncryptedContainer(entries) => {
+                let bytes = Self::encode_container(entries);
+                buf.extend_from_slice(&bytes);
+                Some(())
+            }
+
+            DataValue::Null => Some(()),
+        }
+    }
+
+    fn read_value(cursor: &mut Cursor<&[u8]>, top_level: bool) -> Option<Self> {
+        if top_level {
+            let start = cursor.position() as usize;
+            let remaining = cursor.get_ref().len().checked_sub(start)?;
+            if remaining < 2 {
+                return None;
+            }
+
+            let snapshot = cursor.clone();
+            if let Some(container) = Self::try_read_container(cursor) {
+                return Some(container);
+            }
+            *cursor = snapshot;
+
+            let array = Self::read_array(cursor)?;
+            return Some(array);
+        }
+
+        let kind = cursor.read_u8().ok()?;
+        Self::read_value_by_kind(cursor, kind, None)
+    }
+
+    fn try_read_container(cursor: &mut Cursor<&[u8]>) -> Option<Self> {
+        let count = cursor.read_u16::<BigEndian>().ok()? as usize;
+        let mut entries = Vec::with_capacity(count);
+
+        for _ in 0..count {
+            let kind = cursor.read_u8().ok()?;
+
+            if kind == Self::KIND_BOOL_TRUE || kind == Self::KIND_BOOL_FALSE {
+                let key = DataTypeId(cursor.read_u16::<BigEndian>().ok()?);
+                let value = if kind == Self::KIND_BOOL_TRUE {
+                    DataValue::BoolTrue
+                } else {
+                    DataValue::BoolFalse
+                };
+                entries.push((key, value));
+                continue;
+            }
+
+            let len = cursor.read_u16::<BigEndian>().ok()? as usize;
+            let key = DataTypeId(cursor.read_u16::<BigEndian>().ok()?);
+
+            let start = cursor.position() as usize;
+            let end = start.checked_add(len)?;
+            if end > cursor.get_ref().len() {
+                return None;
+            }
+
+            let payload = &cursor.get_ref()[start..end];
+            let mut inner = Cursor::new(payload);
+            let value = Self::read_value_by_kind(&mut inner, kind, Some(len))?;
+            if inner.position() as usize != len {
+                return None;
+            }
+
+            cursor.set_position(end as u64);
+            entries.push((key, value));
+        }
+
+        Some(DataValue::Container(entries))
+    }
+
+    fn read_array(cursor: &mut Cursor<&[u8]>) -> Option<Self> {
+        let count = cursor.read_u16::<BigEndian>().ok()? as usize;
+        let mut out = Vec::with_capacity(count);
+
+        for _ in 0..count {
+            let kind = cursor.read_u8().ok()?;
+
+            if kind == Self::KIND_BOOL_TRUE {
+                out.push(DataValue::BoolTrue);
+                continue;
+            }
+            if kind == Self::KIND_BOOL_FALSE {
+                out.push(DataValue::BoolFalse);
+                continue;
+            }
+
+            let len = cursor.read_u16::<BigEndian>().ok()? as usize;
+            let start = cursor.position() as usize;
+            let end = start.checked_add(len)?;
+            if end > cursor.get_ref().len() {
+                return None;
+            }
+
+            let payload = &cursor.get_ref()[start..end];
+            let mut inner = Cursor::new(payload);
+            let value = Self::read_value_by_kind(&mut inner, kind, Some(len))?;
+            if inner.position() as usize != len {
+                return None;
+            }
+
+            cursor.set_position(end as u64);
+            out.push(value);
+        }
+
+        Some(DataValue::Array(out))
+    }
+
+    fn read_value_by_kind(
+        cursor: &mut Cursor<&[u8]>,
+        kind: u8,
+        payload_len: Option<usize>,
+    ) -> Option<Self> {
+        match kind {
+            Self::KIND_BOOL_TRUE => Some(DataValue::BoolTrue),
+            Self::KIND_BOOL_FALSE => Some(DataValue::BoolFalse),
+            Self::KIND_SIGNED_NUMBER => Some(DataValue::SignedNumber(
+                cursor.read_i128::<BigEndian>().ok()?,
+            )),
+            Self::KIND_UNSIGNED_NUMBER => Some(DataValue::UnsignedNumber(
+                cursor.read_u128::<BigEndian>().ok()?,
+            )),
+            Self::KIND_FLOAT => {
+                let a = cursor.read_u8().ok()?;
+                let b = cursor.read_u32::<BigEndian>().ok()?;
+                Some(DataValue::Float(a, b))
+            }
+            Self::KIND_STR => {
+                let len = payload_len?;
+                let start = cursor.position() as usize;
+                let end = start.checked_add(len)?;
+                if end > cursor.get_ref().len() {
+                    return None;
+                }
+                let s = std::str::from_utf8(&cursor.get_ref()[start..end])
+                    .ok()?
+                    .to_string();
+                cursor.set_position(end as u64);
+                Some(DataValue::Str(s))
+            }
+            Self::KIND_ARRAY => {
+                let start = cursor.position() as usize;
+                let len = payload_len?;
+                let end = start.checked_add(len)?;
+                if end > cursor.get_ref().len() {
+                    return None;
+                }
+                let mut inner = Cursor::new(&cursor.get_ref()[start..end]);
+                let arr = Self::read_array(&mut inner)?;
+                if inner.position() as usize != len {
+                    return None;
+                }
+                cursor.set_position(end as u64);
+                Some(arr)
+            }
+            Self::KIND_CONTAINER => {
+                let start = cursor.position() as usize;
+                let len = payload_len?;
+                let end = start.checked_add(len)?;
+                if end > cursor.get_ref().len() {
+                    return None;
+                }
+                let mut inner = Cursor::new(&cursor.get_ref()[start..end]);
+                let c = Self::try_read_container(&mut inner)?;
+                if inner.position() as usize != len {
+                    return None;
+                }
+                cursor.set_position(end as u64);
+                Some(c)
+            }
+            #[cfg(feature = "crypto")]
+            Self::KIND_ENCRYPTED_CONTAINER => {
+                let start = cursor.position() as usize;
+                let len = payload_len?;
+                let end = start.checked_add(len)?;
+                if end > cursor.get_ref().len() {
+                    return None;
+                }
+                let mut inner = Cursor::new(&cursor.get_ref()[start..end]);
+                let c = Self::try_read_container(&mut inner)?;
+                if inner.position() as usize != len {
+                    return None;
+                }
+                cursor.set_position(end as u64);
+                if let DataValue::Container(entries) = c {
+                    Some(DataValue::EncryptedContainer(entries))
+                } else {
+                    None
+                }
+            }
+            Self::KIND_NULL => Some(DataValue::Null),
+            _ => None,
+        }
+    }
+
+    fn kind_marker(value: &DataValue) -> u8 {
+        match value {
+            DataValue::BoolTrue => Self::KIND_BOOL_TRUE,
+            DataValue::BoolFalse => Self::KIND_BOOL_FALSE,
+            DataValue::Bool(v) => {
+                if *v {
+                    Self::KIND_BOOL_TRUE
+                } else {
+                    Self::KIND_BOOL_FALSE
+                }
+            }
+            DataValue::SignedNumber(_) => Self::KIND_SIGNED_NUMBER,
+            DataValue::UnsignedNumber(_) => Self::KIND_UNSIGNED_NUMBER,
+            DataValue::Float(_, _) => Self::KIND_FLOAT,
+            DataValue::Str(_) => Self::KIND_STR,
+            DataValue::Array(_) => Self::KIND_ARRAY,
+            DataValue::Bytes(_) => Self::KIND_BYTES,
+            DataValue::Container(_) => Self::KIND_CONTAINER,
+            #[cfg(feature = "crypto")]
+            DataValue::EncryptedContainer(_) => Self::KIND_ENCRYPTED_CONTAINER,
+            DataValue::Null => Self::KIND_NULL,
+        }
+    }
+}
+
+impl PartialEq for DataValue {
+    fn eq(&self, other: &Self) -> bool {
+        use DataValue::*;
+        match (self, other) {
+            (BoolTrue, BoolTrue) | (BoolFalse, BoolFalse) => true,
+            (BoolTrue, Bool(true)) | (Bool(true), BoolTrue) => true,
+            (BoolFalse, Bool(false)) | (Bool(false), BoolFalse) => true,
+            (Bool(a), Bool(b)) => a == b,
+            (SignedNumber(a), SignedNumber(b)) => a == b,
+            (UnsignedNumber(a), UnsignedNumber(b)) => a == b,
+            (Float(a, b), Float(c, d)) => a == c && b == d,
+            (Str(a), Str(b)) => a == b,
+            (Array(a), Array(b)) => a == b,
+            (Bytes(a), Bytes(b)) => a == b,
+            (Container(a), Container(b)) => a == b,
+            #[cfg(feature = "crypto")]
+            (EncryptedContainer(a), EncryptedContainer(b)) => a == b,
+            (Null, Null) => true,
+            _ => false,
+        }
+    }
+}
+
+impl Hash for DataValue {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        use DataValue::*;
+        match self {
+            BoolTrue | Bool(true) => {
+                0u8.hash(state);
+                true.hash(state);
+            }
+            BoolFalse | Bool(false) => {
+                0u8.hash(state);
+                false.hash(state);
+            }
+            SignedNumber(n) => {
+                1u8.hash(state);
+                n.hash(state);
+            }
+            UnsignedNumber(n) => {
+                2u8.hash(state);
+                n.hash(state);
+            }
+            Float(n, m) => {
+                3u8.hash(state);
+                n.hash(state);
+                m.hash(state);
+            }
+            Str(s) => {
+                2u8.hash(state);
+                s.hash(state);
+            }
+            Array(a) => {
+                3u8.hash(state);
+                a.hash(state);
+            }
+            Bytes(a) => {
+                4u8.hash(state);
+                a.hash(state);
+            }
+            Container(c) => {
+                5u8.hash(state);
+                c.hash(state);
+            }
+            #[cfg(feature = "crypto")]
+            EncryptedContainer(c) => {
+                6u8.hash(state);
+                c.hash(state);
+            }
+            Null => {
+                6u8.hash(state);
+            }
+        }
+    }
+}
diff --git a/codec/src/lib.rs b/codec/src/lib.rs
new file mode 100644
index 0000000..071dbe6
--- /dev/null
+++ b/codec/src/lib.rs
@@ -0,0 +1,26 @@
+pub mod communication_types;
+pub mod communication_value;
+pub mod data_value;
+pub mod util;
+
+pub use communication_value::CommunicationValue;
+pub use data_value::{DataKind, DataValue};
+
+pub use util::rand_u32;
+
+pub use type_map::{CommTypeId, DataTypeId, TypeMap, Version};
+
+use common::CodecError;
+
+pub fn encode(_value: &DataValue, _typemap: &TypeMap) -> Result<Vec<u8>, CodecError> {
+    // write header using typemap.data_id(), serialize value
+    todo!()
+}
+
+pub fn decode(_bytes: &[u8], _typemap: &TypeMap) -> Result<DataValue, CodecError> {
+    // read header, look up type names from typemap, build DataValue
+    todo!()
+}
+
+#[cfg(feature = "registry")]
+pub mod registry;
diff --git a/codec/src/registry.rs b/codec/src/registry.rs
new file mode 100644
index 0000000..d7f5ae9
--- /dev/null
+++ b/codec/src/registry.rs
@@ -0,0 +1,67 @@
+use crate::{CodecError, DataValue, decode, encode};
+use std::collections::BTreeMap;
+use type_map::{TypeMap, Version};
+
+#[derive(Clone, Debug)]
+pub struct Registry {
+    versions: BTreeMap<Version, TypeMap>,
+}
+
+impl Registry {
+    pub fn new() -> Self {
+        Self {
+            versions: BTreeMap::new(),
+        }
+    }
+
+    pub fn register(&mut self, typemap: TypeMap) {
+        self.versions.insert(typemap.version.clone(), typemap);
+    }
+
+    pub fn get(&self, version: Version) -> Option<&TypeMap> {
+        self.versions.get(&version)
+    }
+
+    pub fn negotiate(&self, client_versions: &[Version]) -> Option<Version> {
+        client_versions
+            .iter()
+            .filter(|v| self.versions.contains_key(v))
+            .max()
+            .cloned()
+    }
+
+    pub fn latest(&self) -> Option<&TypeMap> {
+        self.versions.last_key_value().map(|(_, v)| v)
+    }
+}
+
+#[derive(Clone, Debug)]
+pub struct VersionedCodec {
+    registry: Registry,
+}
+
+impl VersionedCodec {
+    pub fn new(registry: Registry) -> Self {
+        Self { registry }
+    }
+
+    pub fn encode(&self, value: &DataValue, version: Version) -> Result<Vec<u8>, CodecError> {
+        let typemap = self
+            .registry
+            .get(version)
+            .ok_or(CodecError::UnknownVersion)?;
+        encode(value, typemap)
+    }
+
+    pub fn decode(&self, bytes: &[u8], version: Version) -> Result<DataValue, CodecError> {
+        let typemap = self
+            .registry
+            .get(version)
+            .ok_or(CodecError::UnknownVersion)?;
+        decode(bytes, typemap)
+    }
+
+    pub fn negotiate(&self, client_versions: &[Version]) -> Option<Version> {
+        self.registry.negotiate(client_versions)
+    }
+}
diff --git a/codec/src/util.rs b/codec/src/util.rs
new file mode 100644
index 0000000..db90014
--- /dev/null
+++ b/codec/src/util.rs
@@ -0,0 +1,9 @@
+use rand::random;
+
+pub fn rand_u32() -> u32 {
+    random::<u32>()
+}
+
+pub fn rand_u64() -> u64 {
+    random::<u64>()
+}
diff --git a/common/Cargo.toml b/common/Cargo.toml
new file mode 100644
index 0000000..fa02773
--- /dev/null
+++ b/common/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "common"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
diff --git a/common/src/lib.rs b/common/src/lib.rs
new file mode 100644
index 0000000..0b3c97b
--- /dev/null
+++ b/common/src/lib.rs
@@ -0,0 +1,12 @@
+pub enum RegistryError {
+    ReservedCommId(u8, String),
+}
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum CodecError {
+    UnknownVersion,
+    UnknownCommunicationType(String),
+    UnknownDataType(String),
+    ReservedCommunicationType(u8),
+    InvalidEncoding,
+}
diff --git a/crypto/Cargo.toml b/crypto/Cargo.toml
new file mode 100644
index 0000000..d882c57
--- /dev/null
+++ b/crypto/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "mtp-crypto"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
diff --git a/crypto/src/lib.rs b/crypto/src/lib.rs
new file mode 100644
index 0000000..b93cf3f
--- /dev/null
+++ b/crypto/src/lib.rs
@@ -0,0 +1,14 @@
+pub fn add(left: u64, right: u64) -> u64 {
+    left + right
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn it_works() {
+        let result = add(2, 2);
+        assert_eq!(result, 4);
+    }
+}
diff --git a/host/Cargo.toml b/host/Cargo.toml
new file mode 100644
index 0000000..b35bfb6
--- /dev/null
+++ b/host/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "host"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
diff --git a/host/src/lib.rs b/host/src/lib.rs
new file mode 100644
index 0000000..b93cf3f
--- /dev/null
+++ b/host/src/lib.rs
@@ -0,0 +1,14 @@
+pub fn add(left: u64, right: u64) -> u64 {
+    left + right
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn it_works() {
+        let result = add(2, 2);
+        assert_eq!(result, 4);
+    }
+}
diff --git a/registry/Cargo.toml b/registry/Cargo.toml
new file mode 100644
index 0000000..20e847b
--- /dev/null
+++ b/registry/Cargo.toml
@@ -0,0 +1,7 @@
+[package]
+name = "registry"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+common = { path = "../common" }
diff --git a/registry/src/lib.rs b/registry/src/lib.rs
new file mode 100644
index 0000000..aef951f
--- /dev/null
+++ b/registry/src/lib.rs
@@ -0,0 +1,94 @@
+use common::RegistryError;
+use std::collections::HashMap;
+
+#[repr(transparent)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, PartialOrd, Ord)]
+pub struct CommTypeId(pub u8);
+
+#[repr(transparent)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, PartialOrd, Ord)]
+pub struct DataTypeId(pub u16);
+
+/*
+ * # Reserved Internal Namespace
+ * These are NEVER assigned by a RegistryConfig. They are fixed
+ * across all versions for version negotiation & security.
+ */
+
+pub const INTERNAL_COMM_RESERVED: std::ops::Range<u8> = 0..16;
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum InternalCommType {
+    VersionNegotiate = 0,
+    SecurityHandshake = 1,
+    RegistrySync = 2,
+    // 3-15 reserved for future internal use
+}
+
+impl InternalCommType {
+    pub fn as_id(self) -> CommTypeId {
+        CommTypeId(self as u8)
+    }
+}
+
+#[derive(Clone, Debug)]
+//                (major  , minor  , patch  );
+pub struct Version(pub u16, pub u16, pub u16);
+
+pub struct Registry {
+    pub version: Version,
+    comm_name_to_id: HashMap<String, u8>,
+    comm_id_to_name: HashMap<u8, String>,
+    data_name_to_id: HashMap<String, u16>,
+    data_id_to_name: HashMap<u16, String>,
+}
+
+pub struct RegistryConfig {
+    pub version: Version,
+    pub communication_types: HashMap<String, u8>,
+    pub data_types: HashMap<String, u16>,
+}
+
+impl Registry {
+    pub fn from_config(cfg: RegistryConfig) -> Result<Self, RegistryError> {
+        for (name, &id) in &cfg.communication_types {
+            if INTERNAL_COMM_RESERVED.contains(&id) {
+                return Err(RegistryError::ReservedCommId(id, name.clone()));
+            }
+        }
+
+        let mut comm_id_to_name = HashMap::with_capacity(cfg.communication_types.len());
+        for (name, id) in &cfg.communication_types {
+            comm_id_to_name.insert(*id, name.clone());
+        }
+
+        let mut data_id_to_name = HashMap::with_capacity(cfg.data_types.len());
+        for (name, id) in &cfg.data_types {
+            data_id_to_name.insert(*id, name.clone());
+        }
+
+        Ok(Self {
+            version: cfg.version,
+            comm_name_to_id: cfg.communication_types,
+            comm_id_to_name,
+            data_name_to_id: cfg.data_types,
+            data_id_to_name,
+        })
+    }
+
+    pub fn resolve_comm(&self, name: &str) -> Option<CommTypeId> {
+        self.comm_name_to_id.get(name).copied().map(CommTypeId)
+    }
+
+    pub fn parse_comm(&self, id: CommTypeId) -> Option<&str> {
+        self.comm_id_to_name.get(&id.0).map(|s| s.as_str())
+    }
+
+    pub fn resolve_data(&self, name: &str) -> Option<DataTypeId> {
+        self.data_name_to_id.get(name).copied().map(DataTypeId)
+    }
+
+    pub fn parse_data(&self, id: DataTypeId) -> Option<&str> {
+        self.data_id_to_name.get(&id.0).map(|s| s.as_str())
+    }
+}
diff --git a/transport/Cargo.toml b/transport/Cargo.toml
new file mode 100644
index 0000000..4ac083f
--- /dev/null
+++ b/transport/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "transport"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
diff --git a/transport/src/lib.rs b/transport/src/lib.rs
new file mode 100644
index 0000000..b93cf3f
--- /dev/null
+++ b/transport/src/lib.rs
@@ -0,0 +1,14 @@
+pub fn add(left: u64, right: u64) -> u64 {
+    left + right
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn it_works() {
+        let result = add(2, 2);
+        assert_eq!(result, 4);
+    }
+}
diff --git a/type-map/Cargo.toml b/type-map/Cargo.toml
new file mode 100644
index 0000000..66f916d
--- /dev/null
+++ b/type-map/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "type-map"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
diff --git a/type-map/src/lib.rs b/type-map/src/lib.rs
new file mode 100644
index 0000000..ddba981
--- /dev/null
+++ b/type-map/src/lib.rs
@@ -0,0 +1,28 @@
+use std::collections::HashMap;
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, PartialOrd, Ord)]
+pub struct CommTypeId(pub u8);
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, PartialOrd, Ord)]
+pub struct DataTypeId(pub u16);
+
+#[derive(Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct Version(pub u16);
+
+/// A single protocol version's type dictionary.
+/// Compiled into the client, or loaded by the host via the registry.
+#[derive(Clone, Debug)]
+pub struct TypeMap {
+    pub version: Version,
+    pub comm_types: HashMap<String, u8>,
+    pub data_types: HashMap<String, u16>,
+}
+
+impl TypeMap {
+    pub fn comm_id(&self, name: &str) -> Option<u8> {
+        self.comm_types.get(name).copied()
+    }
+    pub fn data_id(&self, name: &str) -> Option<u16> {
+        self.data_types.get(name).copied()
+    }
+}