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Deploying TLS 1.3: the great, the good and the bad

Improving the encrypted the web, one round-trip at a time

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Video duration
01:01:43
Language
English
Abstract
Transport Layer Security (TLS) 1.3 is almost here. The protocol that protects most of the Internet secure connections is getting the biggest ever revamp, and is losing a round-trip. We will explore differences between TLS 1.3 and previous versions in detail, focusing on the security improvements of the new protocol as well as some of the challenges we face around securely implementing new features such as 0-RTT resumption. At Cloudflare we will be the first to deploy TLS 1.3 on a wide scale, and we’ll be able to discuss the insights we gained while implementing and deploying this protocol.

Version 1.3 is the latest Transport Layer Security (TLS) protocol, which allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery. TLS is the S in HTTPS.

A lot has changed between 1.2 (2008) and 1.3. At the a high level, 1.3 saves a round-trip, making most connections much faster to establish. We'll see how the 1.2 handshake worked, and what had to change to enable 1-RTT handshakes.

But even more importantly, the 1.3 design shifted towards putting robustness first. Anything that is not strictly necessary to the main function of TLS was removed (compression, renegotiation); choices of suboptimal security aren't offered at all (static RSA, CBC, RC4, SHA1, MD5); secure, easy to implement designs are introduced or privileged (RSA-PSS, AEAD implicit nonces, full handshake signatures, Curve25519, resumption forward secrecy). We will go into the why and how of all of these.

But two major trade-offs had to be made: first, 1-RTT handshakes inherently prevent the introduction of encrypted domain names (SNI). We'll see why and what can replace them to provide similar privacy.

Most interestingly, 1.3 comes with 0-RTT resumption. The catch there is that the protocol itself provides no complete protection against replay attacks. We'll unpack the problem, see what mitigations are available, what the risks and attacks are and how that requires careful API design and deployment.

Finally, deployment hasn't been entirely smooth. Many servers out there turned out to be intolerant to 1.3 clients. We'll see what this causes, how it was worked around, and how downgrade protection provides defense in depth.

TLS 1.3 is not in the distant future. The draft is almost finalized, and at Cloudflare we developed an open source stack in Go and support the protocol in beta for all websites. Chrome Canary and Firefox Nightly implement 1.3 clients.

Talk ID
8348
Event:
33c3
Day
1
Room
Saal 2
Start
9:45 p.m.
Duration
01:00:00
Track
Security
Type of
lecture
Speaker
Nick Sullivan
Filippo Valsorda
Talk Slug & media link
33c3-8348-deploying_tls_1_3_the_great_the_good_and_the_bad

Talk & Speaker speed statistics

Very rough underestimation:
138.2 wpm
771.4 spm
While speaker(s) speak(s):
139.6 wpm
776.6 spm
147.2 wpm
822.1 spm
135.7 wpm
753.5 spm
100.0% Checking done100.0%
0.0% Syncing done0.0%
0.0% Transcribing done0.0%
0.0% Nothing done yet0.0%
  
3.3% Checking done3.3%
96.7% Nothing done yet96.7%

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Talk & Speaker speed statistics with word clouds

Whole talk:
138.2 wpm
771.4 spm
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While speakers speak:
139.6 wpm
776.6 spm
tlskeyserverclient1.3sessionticketdata1.2connectiondecrypttimeearlymessagekeyspskhellosendfilippohandshakesharesendscertificatematerialforwardconnectionsdraftdiffie-hellmanapplicationattackerthingfinishedtriprequestapplausecoursehttpsecurityprotocol0-rttresumptiondefinitelynicklistthingscipherroundinsideencryptedinternet
Nick Sullivan:
147.2 wpm
822.1 spm
tls1.3keyapplausedraftfilippo1.2timelistnickservercipherclientlaughsinternetietfprotocolthingspeoplesorthappenedsslsendthingmailingearlierversioncalledfeaturescomplexityprotocolsinvolvedbigrsaworkingdiffie-hellmanyearsnumbergoodchangesecurityversions3.3processsharedworksprivaterunningsimplecommunity
Filippo Valsorda:
135.7 wpm
753.5 spm
serverkeyclientsessiontlsticketdata1.3connection1.2decryptmessagekeysearlypskhellosendsshareapplicationhandshakeforwardmaterialcertificatesendtimetripconnectionsattackercoursefinishedhttpdiffie-hellmanroundrequest0-rttreceivesencryptedinsideresumptionreplayeddefinitelyfilipposupport–>secrecythingticketssecuritybrowsersalgorithm