rustls 0.1.2

Rustls is a modern TLS library written in Rust.


Rustls is a new, 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.

Build Status


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 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.
  • Resumption by clients.
  • Resumption by servers.
  • Client authentication by clients.
  • Client authentication by servers.

Possible future features

  • ECDSA server authentication by servers.
  • PSK support.
  • TLS1.3.
  • Resumption via tickets.
  • OCSP stapling.
  • 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 [--verbose] [-p PORT] [--http]
    [--auth-key KEY --auth-certs CERTS] [--mtu MTU] [--cache CACHE]
    [--cafile CAFILE] [--suite SUITE...] [--proto PROTOCOL...] <hostname>
  tlsclient --version
  tlsclient --help

    -p, --port PORT     Connect to PORT. Default is 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.
    --proto PROTOCOL    Send ALPN extension containing PROTOCOL.
    --cache CACHE       Save session cache to file CACHE.
    --verbose           Emit log output.
    --mtu MTU           Limit outgoing messages to MTU bytes.
    --version           Show tool version.
    --help              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 connection.

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

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

  tlsserver --certs CERTFILE --key KEYFILE [--verbose] [-p PORT]
    [--auth CERTFILE] [--require-auth] [--suite SUITE...]
    [--proto PROTOCOL...] echo
  tlsserver --certs CERTFILE --key KEYFILE [--verbose] [-p PORT]
    [--auth CERTFILE] [--require-auth] [--suite SUITE...]
    [--proto PROTOCOL...] http
  tlsserver --certs CERTFILE --key KEYFILE [--verbose] [-p PORT]
    [--auth CERTFILE] [--require-auth] [--suite SUITE...]
    [--proto PROTOCOL...] forward <fport>
  tlsserver --version
  tlsserver --help

    -p, --port PORT     Listen on PORT. Default is 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,
                        in PEM format.
    --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
    --suite SUITE       Disable default cipher suite list, and use
                        SUITE instead.
    --proto PROTOCOL    Negotiate PROTOCOL using ALPN.
    --verbose           Emit log output.
    --version           Show tool version.
    --help              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.