Enum Content 

pub enum Content {
    Raw(Vec<u8>),
    ChaCha20Poly1305(ChaCha20Poly1305Content),
    Ed25519SelfEncrypted(Ed25519SelfEncryptedContent),
    MlDsaSelfEncrypted(MlDsaSelfEncryptedContent),
    PqxdhEncrypted(PqxdhEncryptedContent),
    EphemeralEcdh(EphemeralEcdhContent),
    Unknown {
        discriminant: u32,
        data: Vec<u8>,
    },
}

Message content variants supporting both raw bytes and encrypted content.

Content Type Design and Versioning Strategy

The Content enum represents the payload of a message and supports different encryption schemes. Important: The choice of available content types and their cryptographic implementations is hard-wired at the message version level (e.g., MessageV0). This means that when a new message version is introduced (like MessageV1), it can have different content variants or updated cryptographic schemes.

Serialization with Postcard

This enum uses postcard for efficient binary serialization. Postcard distinguishes enum variants using a compact binary tag system:

• Raw(Vec<u8>) → serialized as [0, ...data bytes...]
• ChaCha20Poly1305(content) → serialized as [1, ...encrypted content...]
• Ed25519Encrypted(content) → serialized as [2, ...encrypted content...]

The first byte indicates which variant is being deserialized, making the format self-describing and forwards-compatible. For more details on postcard’s enum handling, see: https://docs.rs/postcard/latest/postcard/#enums

Content Type Security Model

Each content type has different security properties and use cases:

Raw - Unencrypted Content

• Used for public messages or when encryption is handled at a higher layer
• Suitable for metadata, public announcements, or already-encrypted data
• No confidentiality protection - readable by all message recipients

ChaCha20Poly1305 - Context-Based Encryption

• Uses ChaCha20-Poly1305 AEAD (Authenticated Encryption with Associated Data)
• Encryption key derived from message context (channel tags, group keys, etc.)
• Provides both confidentiality and authenticity
• Minimal overhead, suitable for high-throughput scenarios

Ed25519Encrypted - Identity-Based Encryption

• Uses Ed25519 keypairs (typically from mnemonic phrases) for key derivation
• Encrypts using ChaCha20-Poly1305 with keys derived from Ed25519 operations
• Suitable for direct peer-to-peer encrypted messaging
• Self-contained encryption that doesn’t require additional context

Version Evolution

When message formats evolve (e.g., MessageV0 → MessageV1), the Content enum can be updated with:

• New encryption schemes (e.g., post-quantum cryptography)
• Additional metadata or structure
• Different key derivation methods
• Backwards-incompatible changes to existing variants

The versioning at the Message level ensures that older clients can gracefully handle unknown message versions while maintaining compatibility with supported versions.

Example Usage

use zoe_wire_protocol::Content;

// Raw content for public data
let public_msg = Content::raw("Hello, world!".as_bytes().to_stdvec());

// Typed content (serialized with postcard)
#[derive(serde::Serialize)]
struct MyData { value: u32 }
let typed_content = Content::raw_typed(&MyData { value: 42 })?;

Variants

Raw(Vec<u8>)

Raw byte content without encryption.

Use this variant for:

• Public messages that don’t require encryption
• Content that is already encrypted at a higher layer
• Metadata or routing information
• Binary data that should be transmitted as-is

ChaCha20Poly1305(ChaCha20Poly1305Content)

ChaCha20-Poly1305 encrypted content with context-derived keys.

The encryption key is determined by message context such as:

• Channel tags and group membership
• Shared secrets established through key exchange
• Derived keys from parent encryption contexts

This variant provides minimal serialization overhead while maintaining strong AEAD security properties.

Ed25519SelfEncrypted(Ed25519SelfEncryptedContent)

Ed25519-derived ChaCha20-Poly1305 self-encrypted content.

Uses sender’s Ed25519 keypair to derive ChaCha20-Poly1305 encryption keys. Only the sender can decrypt this content (encrypt-to-self pattern). Suitable for:

• Personal data storage
• Self-encrypted notes and backups
• Content where only the author should have access

MlDsaSelfEncrypted(MlDsaSelfEncryptedContent)

ML-DSA-derived ChaCha20-Poly1305 self-encrypted content.

Uses sender’s ML-DSA keypair to derive ChaCha20-Poly1305 encryption keys. Only the sender can decrypt this content (encrypt-to-self pattern). Post-quantum secure version of Ed25519SelfEncrypted. Suitable for:

• Personal data storage (post-quantum secure)
• Self-encrypted notes and backups
• Content where only the author should have access

PqxdhEncrypted(PqxdhEncryptedContent)

PQXDH encrypted content.

Uses the PQXDH (Post-Quantum Extended Diffie-Hellman) protocol for asynchronous secure communication establishment. Combines X25519 ECDH with ML-KEM for hybrid classical/post-quantum security. Suitable for:

• Asynchronous RPC initiation (tarpc-over-message)
• Secure inbox messaging
• Initial key agreement for ongoing sessions
• Post-quantum secure communication setup

EphemeralEcdh(EphemeralEcdhContent)

Ephemeral ECDH encrypted content.

Uses ephemeral X25519 key pairs for each message to encrypt for the recipient. Only the recipient can decrypt (proper public key encryption). Provides perfect forward secrecy. Suitable for:

• RPC calls over message infrastructure
• One-off encrypted messages
• Public key encryption scenarios

Unknown

Unknown content type.

This variant is used when the content type is unknown or not supported. It contains the discriminant and the raw data.

Fields

discriminant: u32

data: Vec<u8>

Implementations

impl Content

pub fn raw(data: Vec<u8>) -> Self

Create raw content from bytes

pub fn raw_typed<T: Serialize>(data: &T) -> Result<Self, Error>

Create raw content from serializable object

pub fn encrypted(content: ChaCha20Poly1305Content) -> Self

Create encrypted content

pub fn ed25519_self_encrypted(content: Ed25519SelfEncryptedContent) -> Self

Create ed25519 self-encrypted content

pub fn ml_dsa_self_encrypted(content: MlDsaSelfEncryptedContent) -> Self

Create ML-DSA self-encrypted content

pub fn ephemeral_ecdh(content: EphemeralEcdhContent) -> Self

Create ephemeral ECDH encrypted content

pub fn pqxdh_encrypted(content: PqxdhEncryptedContent) -> Self

Create PQXDH encrypted content

pub fn pqxdh_initial(message: PqxdhInitialMessage) -> Self

Create PQXDH initial message content

pub fn pqxdh_session(message: PqxdhSessionMessage) -> Self

Create PQXDH session message content

pub fn as_raw(&self) -> Option<&Vec<u8>>

Get the raw bytes if this is raw content

pub fn as_encrypted(&self) -> Option<&ChaCha20Poly1305Content>

Get the encrypted content if this is encrypted

pub fn as_ed25519_self_encrypted(&self) -> Option<&Ed25519SelfEncryptedContent>

Get the ed25519 self-encrypted content if this is ed25519 self-encrypted

pub fn as_ml_dsa_self_encrypted(&self) -> Option<&MlDsaSelfEncryptedContent>

Get the ML-DSA self-encrypted content if this is ML-DSA self-encrypted

pub fn as_ephemeral_ecdh(&self) -> Option<&EphemeralEcdhContent>

Get the ephemeral ECDH encrypted content if this is ephemeral ECDH encrypted

pub fn as_pqxdh_encrypted(&self) -> Option<&PqxdhEncryptedContent>

Get the PQXDH encrypted content if this is PQXDH encrypted

pub fn is_encrypted(&self) -> bool

Check if this content is encrypted

pub fn is_raw(&self) -> bool

Check if this content is raw

Trait Implementations

impl Clone for Content

fn clone(&self) -> Content

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Content

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for Content

fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>

where D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl PartialEq for Content

fn eq(&self, other: &Content) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Serialize for Content

fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>

where S: Serializer,

Serialize this value into the given Serde serializer.

impl StructuralPartialEq for Content