Expand description
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.
Non-features
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::WriteRustls 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.
config.root_store.add_server_trust_anchors(&webpki_roots::TLS_SERVER_ROOTS);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();
client.process_new_packets().unwrap();
let mut plaintext = Vec::new();
client.read_to_end(&mut plaintext).unwrap();
io::stdout().write(&plaintext).unwrap();
}
if client.wants_write() && socket.ready_for_write() {
client.write_tls(&mut socket).unwrap();
}
socket.wait_for_something_to_happen();
}Examples
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 thelogcrate. rustls outputs interesting protocol-level messages attrace!anddebug!level, and protocol-level errors atwarn!anderror!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 adangerous()method onClientConfigandServerConfigthat 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 thequicmodule for details of these. You will only need this if you’re writing a QUIC implementation.
Modules
Structs
ClientCertVerifier that will allow both anonymous and authenticated
clients, without any name checking.ClientCertVerifier that will ensure that every client provides a trusted
certificate, without any name checking.StoresClientSessions that stores everything
in memory. It enforces a limit on the number of entries
to bound memory usage.KeyLog implementation that opens a file whose name is
given by the SSLKEYLOGFILE environment variable, and writes
keys into it.StoresClientSessions which does nothing.webpki::TrustAnchor, except it owns
rather than borrows its memory. That prevents lifetimes
leaking up the object tree.StoresServerSessions that stores everything
in memory. If enforces a limit on the number of stored sessions
to bound memory usage.io::Read and io::Write, encapsulating
a Session S and an underlying transport T, such as a socket.io::Read and io::Write, encapsulating
and owning a Session S and an underlying blocking transport
T, such as a socket.ServerCertVerifier, see the trait impl for more information.write_early_data.Enums
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.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.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.Statics
Traits
ClientSession and ServerSession