#OSSPARIS19 - TLS for dummies - MAXIME BESSON, Worteks
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The document discusses the fundamentals of Transport Layer Security (TLS), including cryptographic concepts like symmetric and public key encryption, and the importance of certificate authorities for secure communication. It outlines the TLS process, covering authentication, key exchange, and data exchange while emphasizing the necessity of certificate validation. Additionally, it highlights the efficiency of TLS through the combination of public key cryptography for initial key exchange and symmetric encryption for faster data transfer.
#OSSPARIS19 - TLS for dummies - MAXIME BESSON, Worteks
- 1. TLS for Dummies Maxime Besson info@worteks.com
- 2. 2 (vɔʁ.tɛks) Services Heterogeneous and complex infrastructures, cloud, mail, authentication, security Studies, audit and consulting Technical expertise Technical support Training R&D Edition Collaboration and application portal Mutualized platform for development Identity and Access Management Partnership
- 3. In this talk • A tiny spoonful of cryptography • Public Key Infrastructures, Certificate Authorities • Different types of security
- 4. Our goal • We want to secure communication between two people – On the internet •
- 6. Looks good, let’s do that • But wait, how do you exchange the key in the first place • Can’t do that on the internet, it’s full of eavesdroppers
- 9. And how does this help us? • If Bob sends us his public key, we can send him a message that only he can decrypt • Eve is defeated! • But wait….
- 10. The (wo)man in the middle
- 11. Damned, foiled again • How can we make sure that Bob’s public key belongs to Bob?
- 12. Signature
- 13. So… • Our original goal was confidentiality • • Signature is a different security property: it proves authenticity • • Often combined with a hash function for integrity
- 14. How does signature help us • Bob’s key cannot be signed by Bob because we don’t trust his key yet. • We need a trusted third party
- 16. Certificate Authorities • Organizations that deliver certificates – A document containing a public key, and identity, and some metadata – A signature by the CA’s private key binds links them together • The security of the whole is only as good as the security of the verification process – Mallory can try to have her public key cerfied as Bob’s!
- 17. Does it help us? • Yes, if everybody trusts the Certificate Authority, then all we need to have is the CA’s public key, and we can communicate with anybody!
- 18. Public Key Infrastructure • A system based on Certificate Authorities is one but many possible ways to distribute public keys • Such systems are called Public Key Infrastructures – There are other types (web of trust, blockchain...)
- 19. Let’s sum it up
- 20. Finally, a secure system • (If you don’t mind the all-powerful CA at the center of it all) • Every time either participant wants to send something, it needs to encrypt it with the other participant’s public key • What could go wrong ?
- 21. Too slow ! • Public key cryptography is just too slow • But you know what isn’t? – Symmetric cryptography – But it’s insecure! • UNLESS!
- 22. Best of both worlds • Keys are just messages • We can generate a symmetric key • Send it securely using public-key cryptography • And then, immediately start using it • That way, the performance penalty is only used at the beginning of the connection
- 24. Congratulations • We just invented TLS!
- 25. TLS, in broad strokes • Phase 1: Authentication and key echange – The server authenticates to the client – Sometimes, the client also authenticates to the server – Key exchange occur • Phase 2: Data exchange – Uses symmetric encryption
- 26. Imagine the following scenario
- 27. Certificate validation • When receiving a certificate, we must make sure that – It belongs to the person we wanted to talk to ● For websites, it means that it was issued to the correct domain – It’s not too old or too young – It was signed by a trusted authority – The signature is valid • TLS software does this by default – Don’t disable it – It will make Mallory very happy if you do
- 28. Certificate validation • A certificate ties a public key to an identity • The CA has to do its own verification – Usually, you only need to prove ownership of the domain mentionned in the certificate ● Anyone can get a certificate for https://this.is.google.i.swe.ar/ – EV certificates cover the legal entity behind the request ● They are displayed as a green bar with a company name
- 29. Reality is complicated • In reality, we don’t JUST use a symmetric cipher – Integrity is guaranteed through HMAC or AEAD • There are many versions of TLS – SSL 2.0, SSL 3.0, TLS 1.0, TLS 1.1, TLS 1.2, TLS 1.3 ● Use TLS 1.2, and start planning for TLS 1.3 • Diffie-Hellman key exchange ensures perfect forward secrecy • There are many algorithms and parameters – Usually auto negotiated, but...
- 30. 30 Thanks for your attention More informations: info@worteks.com @worteks_com linkedin.com/company/worteks
- 31. Channel security • CAs like being ambiguous about this • The strength of the symmetric cipher has NOTHING to do with certificates – Except obsolete SGC • But if the certificate is too weak, you are at risk of MITM – You can have a super-strong secure channel to a hacker’s computer
- 32. Will TLS make my website slower • Short answer: no • Long answer: – It makes connection slower ● It’s worth it ● Use keepalive – If you are using modern CPUs, the overhead of the symmetric cipher is insignificant
- 33. What the hell are Elliptic Curves • A mathematical tool used in cryptography (ECC) • Used in public key encryption, so only during the certificate phase • They use smaller keys than the previous RSA scheme – Faster connection time – Lower CPU consumption