tls-parser

Overview

tls-parser is a parser for the TLS protocol. The parser supports protocols SSLv3 to TLSv1.2 (in particular, TLSv1.3 is not supported but will be added).

The parser is based on nom (see nom's documentation for return and error types).

The parser is published on crates.io. To use it, add the following to your Cargo.toml file:

[dependencies]
nom = "1.2.4"
tls-parser = "0.2.1"

Parsing records

The main parsing functions are located in the tls.rs file. The entry functions are:

parse_tls_plaintext: parses a record as plaintext
parse_tls_encrypted: read an encrypted record. The parser has no crypto or decryption features, so the content will be left as opaque data.

extern crate nom;
extern crate tls_parser;

use nom::IResult;
use tls_parser::parse_tls_plaintext;

let bytes = [ 0x16, 0x03, 0x01 ... ];
let res = parse_tls_plaintext(&bytes);
match res {
	IResult::Done(rem,record) => {
		// rem is the remaining data (not parsed)
		// record is an object of type TlsRecord
	},
	IResult::Incomplete(_) => {
		debug!("Defragmentation required (TLS record)");
	},
	IResult::Error(e) => { warn!("parse_tls_record_with_header failed: {:?}",e); }
}
}

Note that knowing if a record is plaintext or not is the responsibility of the caller.

As reading TLS records may imply defragmenting records, some functions are provided to only read the record as opaque data (which ensures the record is complete and gives the record header) and then reading messages from data.

Here is an example of two-steps parsing:

match parse_tls_raw_record(i) {
	IResult::Done(rem, ref r) => {
		match parse_tls_record_with_header(r.data,r.hdr.clone()) {
			IResult::Done(rem2,ref msg_list) => {
				for msg in msg_list {
					// msg has type TlsMessage
				}
			},
			// ...
		}
	},
	// ...
}

Some additional work is required if reading packets from the network, to support reassembly of TCP segments and reassembly of TLS records.

For a complete example of a TLS parser supporting defragmentation and states, see the rusticata/src/tls.rs file of the rusticata crate.

State machine

A TLS state machine is provided in tls_states.rs. The state machine is separated from the parsing functions, and is almost independent. It is implemented as a table of transitions, mainly for the handshake phase.

After reading a TLS message using the previous functions, the TLS state can be updated using the tls_state_transition function. If the transition succeeds, it returns Ok(new_state), otherwise it returns Err(error_state).

// update state machine
match tls_state_transition(self.state, msg) {
	Ok(s)  => self.state = s,
	Err(_) => {
		self.state = TlsState::Invalid;
		self.events.push(TlsParserEvents::InvalidState as u32);
		status |= R_STATUS_EVENTS;
	},
};

Standards

Here is a non-exhaustive list of RFCs this parser is based on:

RFC 2246: The TLS Protocol Version 1.0
RFC 4346: The Transport Layer Security (TLS) Protocol Version 1.1
RFC 4366: Transport Layer Security (TLS) Extensions
RFC 4492: Elliptic Curve Cryptography (ECC) Cipher Suites for Transport Layer Security (TLS)
RFC 4507: Transport Layer Security (TLS) Session Resumption without Server-Side State
RFC 5077: Transport Layer Security (TLS) Session Resumption without Server-Side State
RFC 5246: The Transport Layer Security (TLS) Protocol Version 1.2
RFC 5430: Suite B Profile for Transport Layer Security (TLS)
RFC 5746: Transport Layer Security (TLS) Renegotiation Indication Extension
RFC 6066: Transport Layer Security (TLS) Extensions: Extension Definitions
RFC 6520: Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS) Heartbeat Extension
RFC 6961: The Transport Layer Security (TLS) Multiple Certificate Status Request Extension
RFC 7027: Elliptic Curve Cryptography (ECC) Brainpool Curves for Transport Layer Security (TLS)
RFC 7301: Transport Layer Security (TLS) Application-Layer Protocol Negotiation Extension
RFC 7366: Encrypt-then-MAC for Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)
RFC 7627: Transport Layer Security (TLS) Session Hash and Extended Master Secret Extension
RFC 7919: Negotiated Finite Field Diffie-Hellman Ephemeral Parameters for Transport Layer Security (TLS)
draft-agl-tls-nextprotoneg-03: Transport Layer Security (TLS) Next Protocol Negotiation Extension

FAQ and limitations

Can the parser decrypt a TLS session if I provide the master secret ?

No, it's not implemented

Does the parser support TLS compression ?

No. Note that most TLS implementations disabled it after the FREAK attack, so while detecting compression in ServerHello is possible in tls-parser, it should probably be interpreted as an alert.

Where are located the TLS CipherSuites ?

They are built when running cargo build, to ease updating the list from the IANA TLS parameters.

The file is parsed using a script. During the build, the build.rs parses the list and produces a static, read-only hash table of all known ciphers and their properties.

License

This library is licensed under the GNU Lesser General Public License version 2.1, or (at your option) any later version.

tls-parser 0.2.1