[][src]Crate rustls

Rustls - a modern TLS library

Rustls is a TLS library that aims to provide a good level of cryptographic security, requires no configuration to achieve that security, and provides no unsafe features or obsolete cryptography.

Current features

  • TLS1.2 and TLS1.3.
  • ECDSA, Ed25519 or RSA server authentication by clients.
  • ECDSA, Ed25519 or RSA server authentication by servers.
  • Forward secrecy using ECDHE; with curve25519, nistp256 or nistp384 curves.
  • AES128-GCM and AES256-GCM bulk encryption, with safe nonces.
  • ChaCha20-Poly1305 bulk encryption (RFC7905).
  • ALPN support.
  • SNI support.
  • Tunable MTU to make TLS messages match size of underlying transport.
  • Optional use of vectored IO to minimise system calls.
  • TLS1.2 session resumption.
  • TLS1.2 resumption via tickets (RFC5077).
  • TLS1.3 resumption via tickets or session storage.
  • TLS1.3 0-RTT data for clients.
  • Client authentication by clients.
  • Client authentication by servers.
  • Extended master secret support (RFC7627).
  • Exporters (RFC5705).
  • OCSP stapling by servers.
  • SCT stapling by servers.
  • SCT verification by clients.

Possible future features

  • PSK support.
  • OCSP verification by clients.
  • Certificate pinning.


The following things are broken, obsolete, badly designed, underspecified, dangerous and/or insane. Rustls does not support:

  • SSL1, SSL2, SSL3, TLS1 or TLS1.1.
  • RC4.
  • DES or triple DES.
  • EXPORT ciphersuites.
  • MAC-then-encrypt ciphersuites.
  • Ciphersuites without forward secrecy.
  • Renegotiation.
  • Kerberos.
  • Compression.
  • Discrete-log Diffie-Hellman.
  • Automatic protocol version downgrade.
  • AES-GCM with unsafe nonces.

There are plenty of other libraries that provide these features should you need them.

Platform support

Rustls uses ring for implementing the cryptography in TLS. As a result, rustls only runs on platforms supported by ring. At the time of writing this means x86, x86-64, armv7, and aarch64.

Design Overview

Rustls does not take care of network IO

It doesn't make or accept TCP connections, or do DNS, or read or write files.

There's example client and server code which uses mio to do all needed network IO.

Rustls provides encrypted pipes

These are the ServerSession and ClientSession types. You supply raw TLS traffic on the left (via the read_tls() and write_tls() methods) and then read/write the plaintext on the right:

         TLS                                   Plaintext
         ===                                   =========
    read_tls()      +-----------------------+      io::Read
                    |                       |
          +--------->     ClientSession     +--------->
                    |          or           |
          <---------+     ServerSession     <---------+
                    |                       |
    write_tls()     +-----------------------+      io::Write

Rustls takes care of server certificate verification

You do not need to provide anything other than a set of root certificates to trust. Certificate verification cannot be turned off or disabled in the main API.

Getting started

This is the minimum you need to do to make a TLS client connection.

First, we make a ClientConfig. You're likely to make one of these per process, and use it for all connections made by that process.

let mut config = rustls::ClientConfig::new();

Next we load some root certificates. These are used to authenticate the server. The recommended way is to depend on the webpki_roots crate which contains the Mozilla set of root certificates.

This example is not tested

Now we can make a session. You need to provide the server's hostname so we know what to expect to find in the server's certificate.

let rc_config = Arc::new(config);
let example_com = webpki::DNSNameRef::try_from_ascii_str("example.com").unwrap();
let mut client = rustls::ClientSession::new(&rc_config, example_com);

Now you should do appropriate IO for the client object. If client.wants_read() yields true, you should call client.read_tls() when the underlying connection has data. Likewise, if client.wants_write() yields true, you should call client.write_tls() when the underlying connection is able to send data. You should continue doing this as long as the connection is valid.

The return types of read_tls() and write_tls() only tell you if the IO worked. No parsing or processing of the TLS messages is done. After each read_tls() you should therefore call client.process_new_packets() which parses and processes the messages. Any error returned from process_new_packets is fatal to the session, and will tell you why. For example, if the server's certificate is expired process_new_packets will return Err(WebPKIError(CertExpired)). From this point on, process_new_packets will not do any new work and will return that error continually.

You can extract newly received data by calling client.read() (via the io::Read trait). You can send data to the peer by calling client.write() (via the io::Write trait). Note that client.write() buffers data you send if the TLS session is not yet established: this is useful for writing (say) a HTTP request, but don't write huge amounts of data.

The following code uses a fictional socket IO API for illustration, and does not handle errors.

use std::io;

client.write(b"GET / HTTP/1.0\r\n\r\n").unwrap();
let mut socket = connect("example.com", 443);
loop {
  if client.wants_read() && socket.ready_for_read() {
    client.read_tls(&mut socket).unwrap();

    let mut plaintext = Vec::new();
    client.read_to_end(&mut plaintext).unwrap();

  if client.wants_write() && socket.ready_for_write() {
    client.write_tls(&mut socket).unwrap();



tlsserver and tlsclient are full worked examples. These both use mio.

Crate features

Here's a list of what features are exposed by the rustls crate and what they mean.

  • logging: this makes the rustls crate depend on the log crate. rustls outputs interesting protocol-level messages at trace! and debug! level, and protocol-level errors at warn! and error! level. The log messages do not contain secret key data, and so are safe to archive without affecting session security. This feature is in the default set.

  • dangerous_configuration: this feature enables a dangerous() method on ClientConfig and ServerConfig that allows setting inadvisable options, such as replacing the certificate verification process. Applications requesting this feature should be reviewed carefully.

  • quic: this feature exposes additional constructors and functions for using rustls as a TLS library for QUIC. See the quic module for details of these. You will only need this if you're writing a QUIC implementation.



All defined ciphersuites appear in this module.


Internal classes which may be useful outside the library. The contents of this section DO NOT form part of the stable interface.


This is the rustls manual. This documentation primarily aims to explain design decisions taken in rustls.


APIs for implementing QUIC TLS


Message signing interfaces and implementations.



A ClientCertVerifier that will allow both anonymous and authenticated clients, without any name checking.


A ClientCertVerifier that will ensure that every client provides a trusted certificate, without any name checking.


This type contains a single certificate by value.


Zero-sized marker type representing verification of a client cert chain.


Common configuration for (typically) all connections made by a program.


A struct representing the received Client Hello


This represents a single TLS client session.


An implementor of StoresClientSessions that stores everything in memory. It enforces a limit on the number of entries to bound memory usage.


Accessor for dangerous configuration options.


Marker types. These are used to bind the fact some verification (certificate chain or handshake signature) has taken place into protocol states. We use this to have the compiler check that there are no 'goto fail'-style elisions of important checks before we reach the traffic stage.


KeyLog implementation that opens a file whose name is given by the SSLKEYLOGFILE environment variable, and writes keys into it.


Turns off client authentication.


An implementor of StoresClientSessions which does nothing.


KeyLog that does exactly nothing.


Something which never stores sessions.


This type contains a private key by value.


Something that resolves do different cert chains/keys based on client-supplied server name (via SNI).


A container for root certificates able to provide a root-of-trust for connection authentication.


Zero-sized marker type representing verification of a server cert chain.


Common configuration for a set of server sessions.


This represents a single TLS server session.


An implementor of StoresServerSessions that stores everything in memory. If enforces a limit on the number of stored sessions to bound memory usage.


This type implements io::Read and io::Write, encapsulating a Session S and an underlying transport T, such as a socket.


This type implements io::Read and io::Write, encapsulating and owning a Session S and an underlying blocking transport T, such as a socket.


A cipher suite supported by rustls.


A concrete, safe ticket creation mechanism.


Default ServerCertVerifier, see the trait impl for more information.


Stub that implements io::Write and dispatches to write_early_data.



Bulk symmetric encryption scheme used by a cipher suite.


The CipherSuite TLS protocol enum. Values in this enum are taken from the various RFCs covering TLS, and are listed by IANA. The Unknown item is used when processing unrecognised ordinals.


The ProtocolVersion TLS protocol enum. Values in this enum are taken from the various RFCs covering TLS, and are listed by IANA. The Unknown item is used when processing unrecognised ordinals.


The SignatureScheme TLS protocol enum. Values in this enum are taken from the various RFCs covering TLS, and are listed by IANA. The Unknown item is used when processing unrecognised ordinals.


rustls reports protocol errors using this type.



A list of all the cipher suites supported by rustls.



Something that can verify a client certificate chain


This trait represents the ability to do something useful with key material, such as logging it to a file for debugging.


A trait for the ability to encrypt and decrypt tickets.


A trait for the ability to choose a certificate chain and private key for the purposes of client authentication.


How to choose a certificate chain and signing key for use in server authentication.


Something that can verify a server certificate chain, and verify signatures made by certificates.


Generalises ClientSession and ServerSession


A trait for the ability to store client session data. The keys and values are opaque.


A trait for the ability to store server session data.

Type Definitions