rustls/conn/
kernel.rs

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1//! Kernel connection API.
2//!
3//! This module gives you the bare minimum you need to implement a TLS connection
4//! that does its own encryption and decryption while still using rustls to manage
5//! connection secrets and session tickets. It is intended for use cases like kTLS
6//! where you want to use rustls to establish the connection but want to use
7//! something else to do the encryption/decryption after that.
8//!
9//! There are only two things that [`KernelConnection`] is able to do:
10//! 1. Compute new traffic secrets when a key update occurs.
11//! 2. Save received session tickets sent by a server peer.
12//!
13//! That's it. Everything else you will need to implement yourself.
14//!
15//! # Entry Point
16//! The entry points into this API are
17//! [`UnbufferedClientConnection::dangerous_into_kernel_connection`][client-into]
18//! and
19//! [`UnbufferedServerConnection::dangerous_into_kernel_connection`][server-into].
20//!
21//! In order to actually create an [`KernelConnection`] all of the following
22//! must be true:
23//! - the connection must have completed its handshake,
24//! - the connection must have no buffered TLS data waiting to be sent, and,
25//! - the config used to create the connection must have `enable_extract_secrets`
26//!   set to true.
27//!
28//! This sounds fairly complicated to achieve at first glance. However, if you
29//! drive an unbuffered connection through the handshake until it returns
30//! [`WriteTraffic`] then it will end up in an appropriate state to convert
31//! into an external connection.
32//!
33//! [client-into]: crate::client::UnbufferedClientConnection::dangerous_into_kernel_connection
34//! [server-into]: crate::server::UnbufferedServerConnection::dangerous_into_kernel_connection
35//! [`WriteTraffic`]: crate::unbuffered::ConnectionState::WriteTraffic
36//!
37//! # Cipher Suite Confidentiality Limits
38//! Some cipher suites (notably AES-GCM) have vulnerabilities where they are no
39//! longer secure once a certain number of messages have been sent. Normally,
40//! rustls tracks how many messages have been written or read and will
41//! automatically either refresh keys or emit an error when approaching the
42//! confidentiality limit of the cipher suite.
43//!
44//! [`KernelConnection`] has no way to track this. It is the responsibility
45//! of the user of the API to track approximately how many messages have been
46//! sent and either refresh the traffic keys or abort the connection before the
47//! confidentiality limit is reached.
48//!
49//! You can find the current confidentiality limit by looking at
50//! [`CipherSuiteCommon::confidentiality_limit`] for the cipher suite selected
51//! by the connection.
52//!
53//! [`CipherSuiteCommon::confidentiality_limit`]: crate::CipherSuiteCommon::confidentiality_limit
54//! [`KernelConnection`]: crate::kernel::KernelConnection
55
56use core::marker::PhantomData;
57
58use alloc::boxed::Box;
59
60use crate::client::ClientConnectionData;
61use crate::common_state::Protocol;
62use crate::msgs::codec::Codec;
63use crate::msgs::handshake::{CertificateChain, NewSessionTicketPayloadTls13};
64use crate::quic::Quic;
65use crate::{CommonState, ConnectionTrafficSecrets, Error, ProtocolVersion, SupportedCipherSuite};
66
67/// A kernel connection.
68///
69/// This does not directly wrap a kernel connection, rather it gives you the
70/// minimal interfaces you need to implement a well-behaved TLS connection on
71/// top of kTLS.
72///
73/// See the [`crate::kernel`] module docs for more details.
74pub struct KernelConnection<Data> {
75    state: Box<dyn KernelState>,
76
77    peer_certificates: Option<CertificateChain<'static>>,
78    quic: Quic,
79
80    negotiated_version: ProtocolVersion,
81    protocol: Protocol,
82    suite: SupportedCipherSuite,
83
84    _data: PhantomData<Data>,
85}
86
87impl<Data> KernelConnection<Data> {
88    pub(crate) fn new(state: Box<dyn KernelState>, common: CommonState) -> Result<Self, Error> {
89        Ok(Self {
90            state,
91
92            peer_certificates: common.peer_certificates,
93            quic: common.quic,
94            negotiated_version: common
95                .negotiated_version
96                .ok_or(Error::HandshakeNotComplete)?,
97            protocol: common.protocol,
98            suite: common
99                .suite
100                .ok_or(Error::HandshakeNotComplete)?,
101
102            _data: PhantomData,
103        })
104    }
105
106    /// Retrieves the ciphersuite agreed with the peer.
107    pub fn negotiated_cipher_suite(&self) -> SupportedCipherSuite {
108        self.suite
109    }
110
111    /// Retrieves the protocol version agreed with the peer.
112    pub fn protocol_version(&self) -> ProtocolVersion {
113        self.negotiated_version
114    }
115
116    /// Update the traffic secret used for encrypting messages sent to the peer.
117    ///
118    /// Returns the new traffic secret and initial sequence number to use.
119    ///
120    /// In order to use the new secret you should send a TLS 1.3 key update to
121    /// the peer and then use the new traffic secrets to encrypt any future
122    /// messages.
123    ///
124    /// Note that it is only possible to update the traffic secrets on a TLS 1.3
125    /// connection. Attempting to do so on a non-TLS 1.3 connection will result
126    /// in an error.
127    pub fn update_tx_secret(&mut self) -> Result<(u64, ConnectionTrafficSecrets), Error> {
128        // The sequence number always starts at 0 after a key update.
129        self.state
130            .update_secrets(Direction::Transmit)
131            .map(|secret| (0, secret))
132    }
133
134    /// Update the traffic secret used for decrypting messages received from the
135    /// peer.
136    ///
137    /// Returns the new traffic secret and initial sequence number to use.
138    ///
139    /// You should call this method once you receive a TLS 1.3 key update message
140    /// from the peer.
141    ///
142    /// Note that it is only possible to update the traffic secrets on a TLS 1.3
143    /// connection. Attempting to do so on a non-TLS 1.3 connection will result
144    /// in an error.
145    pub fn update_rx_secret(&mut self) -> Result<(u64, ConnectionTrafficSecrets), Error> {
146        // The sequence number always starts at 0 after a key update.
147        self.state
148            .update_secrets(Direction::Receive)
149            .map(|secret| (0, secret))
150    }
151}
152
153impl KernelConnection<ClientConnectionData> {
154    /// Handle a `new_session_ticket` message from the peer.
155    ///
156    /// This will register the session ticket within with rustls so that it can
157    /// be used to establish future TLS connections.
158    ///
159    /// # Getting the right payload
160    ///
161    /// This method expects to be passed the inner payload of the handshake
162    /// message. This means that you will need to parse the header of the
163    /// handshake message in order to determine the correct payload to pass in.
164    /// The message format is described in [RFC 8446 section 4][0]. `payload`
165    /// should not include the `msg_type` or `length` fields.
166    ///
167    /// Code to parse out the payload should look something like this
168    /// ```no_run
169    /// use rustls::{ContentType, HandshakeType};
170    /// use rustls::kernel::KernelConnection;
171    /// use rustls::client::ClientConnectionData;
172    ///
173    /// # fn doctest(conn: &mut KernelConnection<ClientConnectionData>, typ: ContentType, message: &[u8]) -> Result<(), rustls::Error> {
174    /// let conn: &mut KernelConnection<ClientConnectionData> = // ...
175    /// #   conn;
176    /// let typ: ContentType = // ...
177    /// #   typ;
178    /// let mut message: &[u8] = // ...
179    /// #   message;
180    ///
181    /// // Processing for other messages not included in this example
182    /// assert_eq!(typ, ContentType::Handshake);
183    ///
184    /// // There may be multiple handshake payloads within a single handshake message.
185    /// while !message.is_empty() {
186    ///     let (typ, len, rest) = match message {
187    ///         &[typ, a, b, c, ref rest @ ..] => (
188    ///             HandshakeType::from(typ),
189    ///             u32::from_be_bytes([0, a, b, c]) as usize,
190    ///             rest
191    ///         ),
192    ///         _ => panic!("error handling not included in this example")
193    ///     };
194    ///
195    ///     // Processing for other messages not included in this example.
196    ///     assert_eq!(typ, HandshakeType::NewSessionTicket);
197    ///     assert!(rest.len() >= len, "invalid handshake message");
198    ///
199    ///     let (payload, rest) = rest.split_at(len);
200    ///     message = rest;
201    ///
202    ///     conn.handle_new_session_ticket(payload)?;
203    /// }
204    /// # Ok(())
205    /// # }
206    /// ```
207    ///
208    /// # Errors
209    /// This method will return an error if:
210    /// - This connection is not a TLS 1.3 connection (in TLS 1.2 session tickets
211    ///   are sent as part of the handshake).
212    /// - The provided payload is not a valid `new_session_ticket` payload or has
213    ///   extra unparsed trailing data.
214    /// - An error occurs while the connection updates the session ticket store.
215    ///
216    /// [0]: https://datatracker.ietf.org/doc/html/rfc8446#section-4
217    pub fn handle_new_session_ticket(&mut self, payload: &[u8]) -> Result<(), Error> {
218        // We want to return a more specific error here first if this is called
219        // on a non-TLS 1.3 connection since a parsing error isn't the real issue
220        // here.
221        if self.protocol_version() != ProtocolVersion::TLSv1_3 {
222            return Err(Error::General(
223                "TLS 1.2 session tickets may not be sent once the handshake has completed".into(),
224            ));
225        }
226
227        let nst = NewSessionTicketPayloadTls13::read_bytes(payload)?;
228        let mut cx = KernelContext {
229            peer_certificates: self.peer_certificates.as_ref(),
230            protocol: self.protocol,
231            quic: &self.quic,
232        };
233        self.state
234            .handle_new_session_ticket(&mut cx, &nst)
235    }
236}
237
238pub(crate) trait KernelState: Send + Sync {
239    /// Update the traffic secret for the specified direction on the connection.
240    fn update_secrets(&mut self, dir: Direction) -> Result<ConnectionTrafficSecrets, Error>;
241
242    /// Handle a new session ticket.
243    ///
244    /// This will only ever be called for client connections, as [`KernelConnection`]
245    /// only exposes the relevant API for client connections.
246    fn handle_new_session_ticket(
247        &mut self,
248        cx: &mut KernelContext<'_>,
249        message: &NewSessionTicketPayloadTls13,
250    ) -> Result<(), Error>;
251}
252
253pub(crate) struct KernelContext<'a> {
254    pub(crate) peer_certificates: Option<&'a CertificateChain<'static>>,
255    pub(crate) protocol: Protocol,
256    pub(crate) quic: &'a Quic,
257}
258
259impl KernelContext<'_> {
260    pub(crate) fn is_quic(&self) -> bool {
261        self.protocol == Protocol::Quic
262    }
263}
264
265#[derive(Copy, Clone, Debug, Eq, PartialEq)]
266pub(crate) enum Direction {
267    Transmit,
268    Receive,
269}
rustls/conn/kernel.rs

rustls/conn/
kernel.rs
