rustls 0.12.0

Rustls is a modern TLS library written in Rust.


Rustls is a modern TLS library written in Rust. It's pronounced 'rustles'. It uses ring for cryptography and libwebpki for certificate verification.


Rustls is currently in development and hence unstable. Here's what I'm working on now.

Build Status Coverage Status Documentation

Release history:

  • 0.12.0 (2018-01-06):
    • New API for learning negotiated cipher suite.
    • Move TLS1.3 support from draft 18 to 22.
    • Allow server-side MTU configuration.
    • Tested against latest BoringSSL test suite.
    • Support RFC5705 exporters.
    • Provide ResolvesServerCertUsingSNI for doing SNI-based certificate switching.
    • Allow disabling SNI extension on clients, for use with custom server certificate verifiers where the hostname may not make sense.
    • DNS names are now typesafe, using webpki::DNSName.
    • Update dependencies.
  • 0.11.0 (2017-08-28):
    • New server API for learning requested SNI name.
    • Server now checks selected certificate for validity.
    • Remove time crate dependency.
    • Follow webpki interface changes.
    • Update dependencies.
  • 0.10.0 (2017-08-12):
    • Request and verify SCTs using sct crate. This doesn't happen unless you pass in some certificate transparency logs -- example code does this.
    • Request OCSP stapled response and pass to cert verifier. Note that OCSP verification is not implemented, but this is the public API public change required to support this.
    • Allow OCSP and SCT stapling for servers.
    • Refactor handshake state machines.
    • Bind verifications to final state -- note API change for custom cert verification.
  • 0.9.0 (2017-06-16):
    • Update dependencies.
    • Add IO helper function (complete_io) to rustls::Session.
    • Add blocking stream type -- rustls::Stream -- to ease use on top of blocking sockets.
  • 0.8.0 (2017-05-14):
    • Add dangerous_configuration feature for unsafe features.
  • 0.7.0 (2017-05-08):
    • Update dependencies.
  • 0.6.0 (2017-05-06):
    • Update dependencies.
    • Expose ring's new support for PKCS#8-format private keys.
    • New API for applying limitation to internal buffer sizes.
  • 0.5.8 (2017-03-16):
    • Fix build on later rustc.
  • 0.5.7 (2017-02-27):
    • No changes from 0.5.6; republished with nightly cargo for category support.
  • 0.5.6 (2017-02-19):
    • RFC7627 extended master secret support
    • Assorted documentation improvements
  • 0.5.5 (2017-02-03):
    • Crate categories.
    • Protocol errors now permanent for given session.
    • Exposed ResolvesServerCert trait for customising certification selection.
    • Exposed SignatureScheme enum.
  • 0.5.4 (2017-01-26):
    • First release with TLS1.3-draft-18 support.
    • More performance improvements (now ~15Gbps per core).
    • New API to learn version of negotiated connection.
  • 0.5.0 (2016-09-27):
    • Tickets.
    • Coverage testing.
    • Benchmarking.
    • Massive performance improvements (from ~1Gbps to ~6Gbps per core).
    • OSX support.
    • Minor API corrections and additional testing.


Lives here:


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 (draft 22) only.
  • ECDSA or RSA server authentication by clients.
  • 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.
  • Chacha20Poly1305 bulk encryption.
  • ALPN support.
  • SNI support.
  • Tunable MTU to make TLS messages match size of underlying transport.
  • TLS1.2 session resumption.
  • TLS1.2 resumption via tickets (RFC5077).
  • TLS1.3 resumption via tickets.
  • 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

  • ECDSA server authentication by servers.
  • 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.

Example code

There are two example programs which use mio to do asynchronous IO.

Client example program

The client example program is named tlsclient. The interface looks like:

Connects to the TLS server at hostname:PORT.  The default PORT
is 443.  By default, this reads a request from stdin (to EOF)
before making the connection.  --http replaces this with a
basic HTTP GET request for /.

If --cafile is not supplied, a built-in set of CA certificates
are used from the webpki-roots crate.

  tlsclient [options] [--suite SUITE ...] [--proto PROTO ...] <hostname>
  tlsclient (--version | -v)
  tlsclient (--help | -h)

    -p, --port PORT     Connect to PORT [default: 443].
    --http              Send a basic HTTP GET request for /.
    --cafile CAFILE     Read root certificates from CAFILE.
    --auth-key KEY      Read client authentication key from KEY.
    --auth-certs CERTS  Read client authentication certificates from CERTS.
                        CERTS must match up with KEY.
    --suite SUITE       Disable default cipher suite list, and use
                        SUITE instead.  May be used multiple times.
    --proto PROTOCOL    Send ALPN extension containing PROTOCOL.
                        May be used multiple times to offer serveral protocols.
    --cache CACHE       Save session cache to file CACHE.
    --no-tickets        Disable session ticket support.
    --insecure          Disable certificate verification.
    --verbose           Emit log output.
    --mtu MTU           Limit outgoing messages to MTU bytes.
    --version, -v       Show tool version.
    --help, -h          Show this screen.

Some sample runs:

$ ./tlsclient --http
HTTP/1.1 200 OK
Server: nginx/1.6.2 (Ubuntu)
Date: Wed, 01 Jun 2016 18:44:00 GMT
Content-Type: text/html
Content-Length: 644


$ ./target/debug/examples/tlsclient --http
TLS error: WebPKIError(CertExpired)
Connection closed

Server example program

The server example program is named tlsserver. The interface looks like:

Runs a TLS server on :PORT.  The default PORT is 443.

`echo' mode means the server echoes received data on each connection.

`http' mode means the server blindly sends a HTTP response on each

`forward' means the server forwards plaintext to a connection made to

`--certs' names the full certificate chain, `--key' provides the
RSA private key.

  tlsserver --certs CERTFILE --key KEYFILE [--suite SUITE ...] [--proto PROTO ...] [options] echo
  tlsserver --certs CERTFILE --key KEYFILE [--suite SUITE ...] [--proto PROTO ...] [options] http
  tlsserver --certs CERTFILE --key KEYFILE [--suite SUITE ...] [--proto PROTO ...] [options] forward <fport>
  tlsserver (--version | -v)
  tlsserver (--help | -h)

    -p, --port PORT     Listen on PORT [default: 443].
    --certs CERTFILE    Read server certificates from CERTFILE.
                        This should contain PEM-format certificates
                        in the right order (the first certificate should
                        certify KEYFILE, the last should be a root CA).
    --key KEYFILE       Read private key from KEYFILE.  This should be a RSA
                        private key or PKCS8-encoded private key, in PEM format.
    --ocsp OCSPFILE     Read DER-encoded OCSP response from OCSPFILE and staple
                        to certificate.  Optional.
    --auth CERTFILE     Enable client authentication, and accept certificates
                        signed by those roots provided in CERTFILE.
    --require-auth      Send a fatal alert if the client does not complete client
    --resumption        Support session resumption.
    --tickets           Support tickets.
    --suite SUITE       Disable default cipher suite list, and use
                        SUITE instead.  May be used multiple times.
    --proto PROTOCOL    Negotiate PROTOCOL using ALPN.
                        May be used multiple times.
    --verbose           Emit log output.
    --version, -v       Show tool version.
    --help, -h          Show this screen.

Here's a sample run; we start a TLS echo server, then connect to it with openssl and tlsclient:

$ ./tlsserver --certs test-ca/rsa/end.fullchain --key test-ca/rsa/end.rsa -p 8443 echo &
$ echo hello world | openssl s_client -ign_eof -quiet -connect localhost:8443
depth=2 CN = ponytown RSA CA
verify error:num=19:self signed certificate in certificate chain
hello world
$ echo hello world | ./tlsclient --cafile test-ca/rsa/ca.cert -p 8443 localhost
hello world


Rustls is distributed under the following three licenses:

  • Apache License version 2.0.
  • MIT license.
  • ISC license.

These are included as LICENSE-APACHE, LICENSE-MIT and LICENSE-ISC respectively. You may use this software under the terms of any of these licenses, at your option.