Network Endpoint Data 1 TLS 1.3 : Solving new challenges for - - PowerPoint PPT Presentation

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Network Endpoint Data 1 TLS 1.3 : Solving new challenges for - - PowerPoint PPT Presentation

Sep 22, 2023 305 likes •833 views

Network Endpoint Data 1 TLS 1.3 : Solving new challenges for next-generation firewalls (NGFW) Pass The Salt 2019 2 Who are we ? Nicolas Pamart Damien Deville Thomas Malherbe Apprentice Developer T echnical Leader Developer Does

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Network Endpoint Data

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TLS 1.3 : Solving new challenges for next-generation firewalls (NGFW)

Pass The Salt 2019

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Who are we ?

  • Nicolas Pamart

Apprentice Developer Does stuff, Did not have a choice to talk In front of you nicolas.pamart@stormshield.eu

Damien Deville

T echnical Leader Does stuff damien.deville@stormshield.eu

Thomas Malherbe

Developer Does stuff thomas.malherbe@stormshield.eu www.stormshield.com

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We’re on the network ...

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We protect users & enforce company policy

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With our state of the art IPS

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Focus on TLS application filtering

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TLS : T ransport layer security

A TLS connection TLS in the network stack

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[ ] = Encrypted TLS 1.2 - Handshake TLS 1.2 – Analysed Handshake

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With these data

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But now … TLS 1.3 encrypts server certificate

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Brand new TLS 1.3 handshake

[ ] = Encrypted TLS 1.2 TLS 1.3*

*RFC8446

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We are passive*, we do not decrypt

*On the TLS layer

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Server certificate is a public information

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About certificates

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How-to: Get the same certificate

  • Send the same server name indication (SNI)
  • Propose the same cipherlist
  • Send our own KeyShare extension
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Wait, usually kernels don’t speak TLS !

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Dear userspace daemon, talk for me

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Yay ! We saved our feature

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But for each connection ?!

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Let’s cache certificate !

Pros

  • 0 delay certificate retrieval
  • Less load on server
  • Less load on NGFW

Cons

  • Design the cache : tune entry expiration date & cache size
  • Design the cache #2 : do something that works
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Let’s cache it !

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Let’s cache it !

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How do we identify cache entries ?

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Handling session resumption

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TLS 1.3 session resumption

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TLS 1.3 session resumption : limitations

  • Not really impacting our solution

We base ourselves on ClientHello information => SNI is « theorically* » provided in resumption ClientHello

  • Some malicious peers could not provide SNI during

resumption, thus breaking our filtering

*RFC 8446 section 4.2.11 : Pre-Shared Key Extension

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Simple, just check the presence

  • f SNI no ?
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The problem with SNI

  • SNI is not mandatory ...
  • Need to check if original session was initiated with SNI
  • How to do that ?
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Another cache … for the SNI !

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The big picture

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SNI not coherent

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SNI coherent & Cache HIT - PASS

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SNI coherent & Cache HIT - BLOCK

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SNI coherent & Cache MISS - PASS

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Proof of concept

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PoC : design

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PoC : supported features

  • SNI coherence cache
  • Certificate Caching
  • Application blacklisting

=> Statistics gathering

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PoC : results for 1 day / 1 user

Cache misses: 259 SNI incoherences : 0 Total: 2509 => Ratio: 10.32% cache miss

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Final note

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World is safer now

  • Facebook is blocked again
  • That’s how we saved the world
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www.stormshield.com/join-us/

20+ Open jobs!

Villeneuve d’Ascq – Paris (ILM) - Lyon

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22, rue du Gouverneur Général Éboué 92130 Issy-les-Moulineaux FRANCE nicolas.pamart@stormshield.eu +33 (0) 9 69 32 96 29

Get in T

  • uch

Thank you

Looking forward to hearing from you

damien.deville@stormshield.eu thomas.malherbe@stormshield.eu

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About encrypted SNI (eSNI)

  • Currently as a draft
  • Can break our solution as we are not able do
  • btain the SNI
  • Encrypted via key given in DNS

=> Solution: We also analyze DNS trafic (If you use DNSsec on top of that you may beat us)

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TLS in kernel

  • Requires to have the whole chain of cert in kernel

=> Not enough memory to do that, too costly

  • It is technically possible to do TLS in kernel
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About PSK-only servers (if it exists)

  • PSK can be used to authenticate server

=> Thus no need for server certificate => Our solution don’t work (or don’t apply)

  • Solution: Whitelist PSK-only servers
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TLS 1.3 early-data

  • Stripped when mimicking ClientHello
  • Concerns about anti-replay
  • We can’t provide sufficient security for anti-replay
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TLS 1.2 handshake

[ ] = Encrypted

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TLS 1.3 handshake

[ ] = Encrypted

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TLS 1.3 session resumption

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TLS 1.3 0-RT == Resumption + Early data