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THE CASE FOR PREFETCHING AND PREVALIDATING TLS SERVER CERTIFICATES

THE CASE FOR PREFETCHING AND PREVALIDATING TLS SERVER CERTIFICATES. Emily Stark, Lin- Shung Huang, Dinesh Israni , Collin Jackson, Dan Boneh Presented by: Nurul Atiqah Abu Talib. INTRODUCTION. P refetch and prevalidate server certificates before a user clicks on an HTTPS link

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THE CASE FOR PREFETCHING AND PREVALIDATING TLS SERVER CERTIFICATES

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  1. THE CASE FOR PREFETCHING AND PREVALIDATING TLS SERVER CERTIFICATES Emily Stark, Lin-Shung Huang, Dinesh Israni, Collin Jackson, Dan Boneh Presented by: NurulAtiqah Abu Talib

  2. INTRODUCTION • Prefetch and prevalidate server certificates before a user clicks on an HTTPS link • Combines with Snap Start • less costly • removing time pressure from the certificate validation process

  3. TRANSPORT LAYER SECURITY (TLS) • A protocol for encrypting and authenticating traffic between a client and a server

  4. TLS HANDSHAKE Certificate validation Initialize Handshake Certificate Certificate valid? Response Negotiate Key Negotiate Key HTTP Request HTTP Respond

  5. Online Certificate Status Protocol (OCSP) • Client asks OCSP responder whether certificate is valid • Responder specifies how long response is valid

  6. TLS PROBLEMS • Common TLS misconfigurations and certificate warnings • TLS-enabled servers face heavier load • discourages site-wide use of TLS, thereby exposing users to session hijacking and other exploits • increases client latency

  7. TLS SNAP START (1/2) • Zeroround trip handshake Initialize Handshake Certificate Certificate valid? Negotiate Key Negotiate Key HTTP Request HTTP Respond

  8. TLS SNAP START (2/2) • Zeroround trip handshake Initialize Handshake Snap Start Extension HTTP Request HTTP Respond

  9. SNAP START CHALLENGE I (1/2) • First visit: Initialize Handshake Snap Start Extension Selected Cipher Suite + orbit Cache

  10. SNAP START CHALLENGE I (2/2) • Next visit: • Client must know server certificate • Cached from previous visit Initialize Handshake Snap Start Extension + necessary information from cache HTTP Request HTTP Respond

  11. SNAP START CHALLENGE II • If cached certificate’svalidation status from a previous handshake has expired, the browser still must communicate with a certificate validation authority

  12. CONTRIBUTION • Detailed statistics from OCSP responders in the real world • Certificateprefetchingandprevalidation • Proposefourprefetchingstrategies • Compare strategies and benefits • Implementation

  13. OCSP IN THE WILD • Experimental setup • OCSP response times collected from users running Perspectives browser extensions • 242 clients, 4474 certificates, 24 responders

  14. OCSP MEASUREMENTS (1/2) • Cumulative distribution of OCSP lookup response times Mean: 498 ms Median: 291 ms

  15. OCSP MEASUREMENTS (2/2) • Cumulative distribution of OCSP lookup response times 74.8%

  16. METHOD • Prefetchcertificates • Enables Snap Start handshakes more frequently • Prevalidate certificates • Removes OCSP lookup from critical path • Question: • When to prefetch? When to prevalidate? • Howtoobtaincertificates?

  17. WHEN TO PREFETCH? • Idea from DNS prefetching • To increase responsiveness, resolves domain names before the user clicks on a link • Triggered when: • While the user is typing • Mouse hovers over a link • During browser startup

  18. HOW TO PREFETCH? • Naïve Method: Open TLS connection and obtain information • Challenge: Full TLS handshake is expensive

  19. SERVER CERTIFICATE PREFETCHING AND PREVALIDATING Prefetching with a truncated handshake Prefetching via HTTP GET Prefetching from a CDN Prefetching from DNS

  20. PREFETCHING WITH A TRUNCATED HANDSHAKE (1/2) Initialize Handshake Certificate Alert Message

  21. PREFETCHING WITH A TRUNCATED HANDSHAKE (2/2)

  22. PREFETCHING VIA HTTP GET

  23. PREFETCHING FROM A CDN

  24. PREFETCHING FROM DNS

  25. PREVALIDATE

  26. ANALYSIS • How much does prefetching and prevalidating affect handshake latency?

  27. HANDSHAKE LATENCY Remove round trips by using Snap Start Remove OCSP by prevalidating certificate and using snap start

  28. CONCLUSION (CONT’D) • Client latency from TLS handshakes costs websites in traffic and revenue, and discourages websites from using TLS • Server certificate prefetching and prevalidation • Snap Start handshake with a prevalidated certificate • four times faster than a normal TLS handshake • 74.8% of OCSP lookups took between 100 ms and 600 ms • Prefetching enables an even more dramatic speed-up over standard TLS

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