TLS 1.3 + TCP Fast Open

1. TCP Fast Open added support to send data in the first packet of the TCP handshake.
2. TLS 1.3 added support for 0-RTT, allowing to send application data in the first packet of the TLS handshake.

which makes it possible to establish a encrypted connection and send the application over TCP in one packet.

TL;DR

1. using TLS 1.3 instead of TLS 1.2 saves a round-trip in the full handshake
2. session resumption saves about 5-8ms
3. TLS 1.3 0-RTT saves another round-trip
4. TCP Fast Open saves another round-trip

Scenario

A simple use case

1. establish connection
2. send PING
3. receive PONG
4. close connection

over a network with a round-trip-time (RTT) of

• 200ms (between DCs, different region)
• 20ms (between DCs, same region)
• 2ms (in a DC)
• 0.2ms (LAN)
• 0.02ms (loopback)

RTT 200ms

TLS Version	Full Handshake	Full Handshake + TFO	Resumption	Resumption + TFO
TLS 1.0, 1.1, 1.2	809.50ms	609.20ms	704.90ms	504.80ms
TLS 1.3	609.30ms	409.40ms	602.60ms	402.50ms

RTT 20ms

TLS Version	Full Handshake	Full Handshake + TFO	Resumption	Resumption + TFO
TLS 1.0, 1.1, 1.2	88.92ms	69.13ms	74.88ms	54.82ms
TLS 1.3	69.20ms	49.17ms	62.52ms	42.53ms

Note: TFO is TCP Fast Open.

RTT 2ms

TLS Version	Full Handshake	Full Handshake + TFO	Resumption	Resumption + TFO
TLS 1.0, 1.1, 1.2	15.26ms	13.67ms	11.51ms	9.93ms
TLS 1.3	13.07ms	11.30ms	8.28ms	6.27ms

RTT 0.2ms

TLS Version	Full Handshake	Full Handshake + TFO	Resumption	Resumption + TFO
TLS 1.0, 1.1, 1.2	5.92ms	6.03ms	3.59ms	3.68ms
TLS 1.3	6.56ms	6.28ms	2.58ms	2.47ms

Examples

Build Requirements

• cmake 3.4 or later
• C++14 capable compiler
• Openssl 1.1.1
• Operating Systems
  • Linux 4.11 or later
  • FreeBSD 12 or later
  • MacOSX 10.11 or later
  • Windows 10

building

Configure the build:

$ cmake

Run the build with:

$ cmake --build .

Note: cmake --build . runs the build. On Unix it will run "make", on windows it will run "msbuild".

MacOS X/Windows

On MacOS X and Windows you need to pass -DOPENSSL_ROOT_DIR= to cmake:

$ cmake -DOPENSSL_ROOT_DIR=<path-to-openssl-binary-directory>
$ cmake --build .

Note: On MacOS X it is needed as linking against the systems openssl will fail.

running

1. Start server in one terminal

   $ ./src/tls13_ping_pong_server --port=3308
   

2. run the client in another terminal

   $ ./src/tls13_ping_pong_client --port=3308
   

Tracing packets

Start server as before, but add tcpdump:

$ sudo tcpdump -w tls13.pcap -i lo 'port 3308'
$ ./src/tls13_ping_pong_client --port=3308
$ wireshark tls13.pcap

Note: On FreeBSD and MacOS X use lo0 as name for the loopback interface.

Let wireshark decrypt the TLS packets automatically

Wireshark 3.x allows to add the session keys that were used for the connection into the pcap file:

$ sudo tcpdump -w tls13.pcap -i lo 'port 3308'
$ SSLKEYLOGFILE=keys.txt ./src/tls13_ping_pong_client --port=3308
$ editcap --inject-secrets tls,keys.txt tls13.pcap tls13-with-keys-dsb.pcapng
$ wireshark tls13-with-keys-dsb.pcapng

Adding latency

On Linux, to simulate real-life network delays all packets from and to port 3308 were delayed by 10ms by using the netem network emulator of tc.

$ sudo tc qdisc add dev lo root handle 1: prio
$ sudo tc qdisc add dev lo parent  1:3 handle 30: netem delay 10ms
$ sudo tc filter add dev lo parent 1:0 protocol ip u32 match ip dport 3308 0xffff flowid 1:3
$ sudo tc filter add dev lo parent 1:0 protocol ip u32 match ip sport 3308 0xffff flowid 1:3