openmls/framing/
public_message.rs

//! # PublicMessage
//!
//! A PublicMessage is a framing structure for MLS messages. It can contain
//! Proposals, Commits and application messages.

use std::io::Write;

use openmls_traits::{crypto::OpenMlsCrypto, types::Ciphersuite};
use tls_codec::{
    Serialize as TlsSerializeTrait, TlsDeserialize, TlsDeserializeBytes, TlsSerialize, TlsSize,
};

use super::{
    mls_auth_content::{AuthenticatedContent, FramedContentAuthData},
    mls_content::{framed_content_tbs_serialized_detached, AuthenticatedContentTbm, FramedContent},
    *,
};
use crate::{error::LibraryError, versions::ProtocolVersion};

/// Wrapper around a `Mac` used for type safety.
#[derive(
    Debug,
    PartialEq,
    Clone,
    Serialize,
    Deserialize,
    TlsSerialize,
    TlsDeserialize,
    TlsDeserializeBytes,
    TlsSize,
)]
pub(crate) struct MembershipTag(pub(crate) Mac);

/// [`PublicMessage`] is a framing structure for MLS messages. It can contain
/// Proposals, Commits and application messages.
///
/// 9. Message framing
///
/// ```c
/// // draft-ietf-mls-protocol-17
///
/// struct {
///     FramedContent content;
///     FramedContentAuthData auth;
///     optional<MAC> membership_tag;
/// } PublicMessage;
/// ```
#[derive(Debug, PartialEq, Clone, Serialize, Deserialize)]
pub struct PublicMessage {
    pub(crate) content: FramedContent,
    pub(crate) auth: FramedContentAuthData,
    pub(crate) membership_tag: Option<MembershipTag>,
}

#[cfg(test)]
impl PublicMessage {
    pub(crate) fn content(&self) -> &crate::framing::mls_content::FramedContentBody {
        &self.content.body
    }

    pub fn set_confirmation_tag(&mut self, confirmation_tag: Option<ConfirmationTag>) {
        self.auth.confirmation_tag = confirmation_tag;
    }

    pub fn unset_membership_tag(&mut self) {
        self.membership_tag = None;
    }

    pub(crate) fn set_content(&mut self, content: FramedContentBody) {
        self.content.body = content;
    }

    pub fn set_epoch(&mut self, epoch: u64) {
        self.content.epoch = epoch.into();
    }

    pub fn confirmation_tag(&self) -> Option<&ConfirmationTag> {
        self.auth.confirmation_tag.as_ref()
    }

    pub(crate) fn invalidate_signature(&mut self) {
        let mut modified_signature = self.auth.signature.as_slice().to_vec();
        modified_signature[0] ^= 0xFF;
        self.auth.signature.modify(&modified_signature);
    }

    /// Set the sender.
    pub(crate) fn set_sender(&mut self, sender: Sender) {
        self.content.sender = sender;
    }

    /// Set the group id.
    pub(crate) fn set_group_id(&mut self, group_id: GroupId) {
        self.content.group_id = group_id;
    }

    /// Returns `true` if this is a handshake message and `false` otherwise.
    pub(crate) fn is_handshake_message(&self) -> bool {
        self.content_type().is_handshake_message()
    }
    // TODO: #727 - Remove if not needed.
    // #[cfg(test)]
    // pub(super) fn set_signature(&mut self, signature: Signature) {
    //     self.signature = signature;
    // }

    // #[cfg(test)]
    // pub(super) fn set_membership_tag_test(&mut self, tag: MembershipTag) {
    //     self.membership_tag = Some(tag);
    // }
}

impl From<AuthenticatedContent> for PublicMessage {
    fn from(v: AuthenticatedContent) -> Self {
        Self {
            content: v.content,
            auth: v.auth,
            membership_tag: None,
        }
    }
}

impl PublicMessage {
    /// Returns the [`ContentType`] of the message.
    pub fn content_type(&self) -> ContentType {
        self.content.body.content_type()
    }

    /// Get the sender of this message.
    pub(crate) fn sender(&self) -> &Sender {
        &self.content.sender
    }

    /// Adds a membership tag to this `PublicMessage`. The membership_tag is
    /// produced using the the membership secret.
    ///
    /// This should be used after signing messages from group members.
    pub(crate) fn set_membership_tag(
        &mut self,
        crypto: &impl OpenMlsCrypto,
        ciphersuite: Ciphersuite,
        membership_key: &MembershipKey,
        serialized_context: &[u8],
    ) -> Result<(), LibraryError> {
        let tbs_payload = framed_content_tbs_serialized_detached(
            ProtocolVersion::default(),
            WireFormat::PublicMessage,
            &self.content,
            &self.content.sender,
            serialized_context,
        )
        .map_err(LibraryError::missing_bound_check)?;
        let tbm_payload = AuthenticatedContentTbm::new(&tbs_payload, &self.auth)?;
        let membership_tag = membership_key.tag_message(crypto, ciphersuite, tbm_payload)?;

        self.membership_tag = Some(membership_tag);
        Ok(())
    }

    #[cfg(test)]
    pub(crate) fn set_membership_tag_test(&mut self, membership_tag: MembershipTag) {
        self.membership_tag = Some(membership_tag);
    }

    // TODO: #727 - Remove if not needed.
    // #[cfg(test)]
    // pub(crate) fn invalidate_signature(&mut self) {
    //     let mut modified_signature = self.signature().as_slice().to_vec();
    //     modified_signature[0] ^= 0xFF;
    //     self.signature.modify(&modified_signature);
    // }
}

#[cfg(test)]
impl From<PublicMessage> for FramedContentTbs {
    fn from(v: PublicMessage) -> Self {
        FramedContentTbs {
            version: ProtocolVersion::default(),
            wire_format: WireFormat::PublicMessage,
            content: v.content,
            serialized_context: None,
        }
    }
}

// -------------------------------------------------------------------------------------------------

/// ```c
/// // draft-ietf-mls-protocol-17
/// struct {
///     WireFormat wire_format;
///     FramedContent content; /* with content_type == commit */
///     opaque signature<V>;
///} ConfirmedTranscriptHashInput;
/// ```
#[derive(TlsSerialize, TlsSize)]
pub(crate) struct ConfirmedTranscriptHashInput<'a> {
    pub(super) wire_format: WireFormat,
    pub(super) mls_content: &'a FramedContent,
    pub(super) signature: &'a Signature,
}

impl ConfirmedTranscriptHashInput<'_> {
    pub(crate) fn calculate_confirmed_transcript_hash(
        self,
        crypto: &impl OpenMlsCrypto,
        ciphersuite: Ciphersuite,
        interim_transcript_hash: &[u8],
    ) -> Result<Vec<u8>, LibraryError> {
        let serialized: Vec<u8> = self
            .tls_serialize_detached()
            .map_err(LibraryError::missing_bound_check)?;

        crypto
            .hash(
                ciphersuite.hash_algorithm(),
                &[interim_transcript_hash, &serialized].concat(),
            )
            .map_err(LibraryError::unexpected_crypto_error)
    }
}

impl<'a> TryFrom<&'a AuthenticatedContent> for ConfirmedTranscriptHashInput<'a> {
    type Error = &'static str;

    fn try_from(mls_content: &'a AuthenticatedContent) -> Result<Self, Self::Error> {
        if !matches!(mls_content.content().content_type(), ContentType::Commit) {
            return Err("PublicMessage needs to contain a Commit.");
        }

        Ok(ConfirmedTranscriptHashInput {
            wire_format: mls_content.wire_format(),
            mls_content: &mls_content.content,
            signature: mls_content.signature(),
        })
    }
}

// -------------------------------------------------------------------------------------------------

/// ```c
/// // draft-ietf-mls-protocol-17
/// struct {
///     MAC confirmation_tag;
/// } InterimTranscriptHashInput;
/// ```
#[derive(TlsSerialize, TlsSize)]
pub(crate) struct InterimTranscriptHashInput<'a> {
    pub(crate) confirmation_tag: &'a ConfirmationTag,
}

impl InterimTranscriptHashInput<'_> {
    pub fn calculate_interim_transcript_hash(
        self,
        crypto: &impl OpenMlsCrypto,
        ciphersuite: Ciphersuite,
        confirmed_transcript_hash: &[u8],
    ) -> Result<Vec<u8>, LibraryError> {
        let serialized = self
            .tls_serialize_detached()
            .map_err(LibraryError::missing_bound_check)?;

        crypto
            .hash(
                ciphersuite.hash_algorithm(),
                &[confirmed_transcript_hash, &serialized].concat(),
            )
            .map_err(LibraryError::unexpected_crypto_error)
    }
}

impl<'a> TryFrom<&'a PublicMessage> for InterimTranscriptHashInput<'a> {
    type Error = &'static str;

    fn try_from(public_message: &'a PublicMessage) -> Result<Self, Self::Error> {
        match public_message.auth.confirmation_tag.as_ref() {
            Some(confirmation_tag) => Ok(InterimTranscriptHashInput { confirmation_tag }),
            None => Err("PublicMessage needs to contain a confirmation tag."),
        }
    }
}

impl<'a> From<&'a ConfirmationTag> for InterimTranscriptHashInput<'a> {
    fn from(confirmation_tag: &'a ConfirmationTag) -> Self {
        InterimTranscriptHashInput { confirmation_tag }
    }
}

// -------------------------------------------------------------------------------------------------

impl Size for PublicMessage {
    #[inline]
    fn tls_serialized_len(&self) -> usize {
        self.content.tls_serialized_len()
            + self.auth.tls_serialized_len()
            + if let Some(membership_tag) = &self.membership_tag {
                membership_tag.tls_serialized_len()
            } else {
                0
            }
    }
}

impl TlsSerializeTrait for PublicMessage {
    fn tls_serialize<W: Write>(&self, writer: &mut W) -> Result<usize, tls_codec::Error> {
        // Serialize the content, not the TBS.
        let mut written = self.content.tls_serialize(writer)?;
        written += self.auth.tls_serialize(writer)?;
        written += if let Some(membership_tag) = &self.membership_tag {
            membership_tag.tls_serialize(writer)?
        } else {
            0
        };
        Ok(written)
    }
}
openmls/framing/public_message.rs

openmls/framing/
public_message.rs
