Trusted Browsers for Uncertain Times David Kohlbrenner and Hovav - - PowerPoint PPT Presentation

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Trusted Browsers for Uncertain Times David Kohlbrenner and Hovav - - PowerPoint PPT Presentation

May 12, 2023 521 likes •1.39k views

Trusted Browsers for Uncertain Times David Kohlbrenner and Hovav Shacham UC San Diego Building a browser that can provably mitigate timing attacks Trusted Browsers Time and web browsers Mitigating attacks for A trusted browser

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SLIDE 1

Trusted Browsers for Uncertain Times

David Kohlbrenner and Hovav Shacham UC San Diego

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SLIDE 2

Building a browser that can provably mitigate timing attacks

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SLIDE 3

Trusted Browsers for Uncertain Times

  • Time and web browsers
  • Mitigating attacks
  • A trusted browser
  • A (less) trusted browser
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SLIDE 4

Timing attacks

  • Time and web browsers
  • Mitigating attacks
  • A trusted browser
  • A (less) trusted browser
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SLIDE 5

Browsers and timing attacks

  • Browser has multiple privilege levels

○ User secrets ○ System secrets ○ Origin secrets

  • Browsers expose detailed information

○ performance.now() ○ getAnimationFrame()

  • Browsers compute and communicate between levels
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SLIDE 6

Timing attacks in web browsers

  • SVG Filter cross-origin pixel stealing
  • JavaScript cache timing attacks
  • Fingerprinting
  • History Sniffing
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SLIDE 7

What is being done about it? - SVG attack

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SLIDE 8

What is being done about it? - Cache attack

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SLIDE 9

What is being done about it? - Cache attack

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SLIDE 10

Unfortunately, this doesn’t work.

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SLIDE 11

Better clocks with edges

  • Time and web browsers
  • Mitigating attacks
  • A trusted browser
  • A (less) trusted browser
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SLIDE 12

Rounding down the clock

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SLIDE 13

Clock-edge technique

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SLIDE 14

Clock-edge technique - performance.now()

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SLIDE 15

Clock-edge technique - performance.now()

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SLIDE 16

Implicit clocks in the browser

  • Time and web browsers
  • Mitigating attacks
  • A trusted browser
  • A (less) trusted browser
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SLIDE 17

Implicit clocks - Techniques

  • <video> frames
  • Web Speech
  • <video> played
  • setTimeout()
  • CSS Animations
  • WebVTT API
  • XHRs with cooperating server
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SLIDE 18

Implicit clocks - Techniques

  • <video> frames
  • Web Speech
  • <video> played
  • setTimeout()
  • CSS Animations
  • WebVTT API
  • XHRs with cooperating server

Probably many many more!

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SLIDE 19

Implicit clocks - WebVTT

  • Subtitles for <video> elements
  • Specified in a .vtt file

○ WEBVTT 00:00:00.000 --> 00:00:00.001 A very short duration subtitle

  • Specifies arbitrary subtitles with 1ms granularity
  • track.activeCues returns all displayed subtitles
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SLIDE 20

Implicit clocks - WebVTT

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SLIDE 21

Implicit clocks - WebVTT and clock-edge

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SLIDE 22

How to mitigate timing attacks

  • Time and web browsers
  • Mitigating attacks
  • A trusted browser
  • A (less) trusted browser
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SLIDE 23

Degrade all clocks available to the attacker.

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SLIDE 24

Fuzzy time for the VAX security kernel

  • “[A] collection of techniques that reduces the bandwidths of covert timing

channels by making all clocks available to a process noisy.”

  • “Reducing Timing Channels with Fuzzy Time”

○ Hu at Oakland 1991!

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SLIDE 25

Covert channels

  • Two clocks
  • Modulated

○ The channel

  • Reference

○ Wall clock, etc

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SLIDE 26

Fuzzy time for the VAX security kernel

  • VAX VMM

○ Single thread per VM ○ Clean VM interface

  • All I/O is asynchronous
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SLIDE 27

Fuzzy time - Problem

  • Ineffective countermeasures to disk covert channel

○ Cannot be closed ○ Not auditable ○ Added noise impractical ○ No hardware solution

  • Plenty of other potential ‘shared buses’
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SLIDE 28

Fuzzy time - Solution

  • “reduce the accuracy and precision of system clocks”
  • “randomly alter the timings of I/O operations”
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SLIDE 29

Fuzzy time - Solution

  • Explicit clocks

○ “make the interval-timer interrupt random”

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SLIDE 30

Fuzzy time - Solution

  • Explicit clocks

○ “make the interval-timer interrupt random”

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SLIDE 31

Fuzzy time - Solution

  • Explicit clocks

○ “make the interval-timer interrupt random”

  • Implicit clocks

○ “[use] random clock ticks … to make fuzzy the clocks derived from I/O operations” ○ “Add new buffers … for all I/O operations”

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SLIDE 32

Fuzzy time - Solution guarantees

  • Degraded clocks

○ Limit the bandwidth

  • Time granularity

○ g

  • Bounded channel bandwidth

○ For any timing covert channel ○ ~

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SLIDE 33

Next queue Currently queued

Fuzzy time - I/O queuing

Active Todo Active Active

Response queue

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SLIDE 34

Next queue Currently queued

Fuzzy time - I/O queuing

Active Todo Todo Active Active

Response queue

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SLIDE 35

Next queue Currently queued

Fuzzy time - I/O queuing

Active Todo Todo Active Active

Response queue

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SLIDE 36

Next queue Currently queued

Fuzzy time - I/O queuing

Active Todo Todo Active

Response queue

Done Todo

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SLIDE 37

Next queue Currently queued

Fuzzy time - I/O queuing

Active Todo Todo

Response queue

Done Todo Done Todo

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SLIDE 38

Next queue Currently queued

Fuzzy time - I/O queuing

Active Todo Todo

Response queue

Done Todo Done Todo Active Active

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SLIDE 39

Next queue Currently queued

Fuzzy time - I/O queuing

Active

Response queue

Done Todo Done Todo Active Active

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SLIDE 40

Next queue Currently queued

Fuzzy time - I/O queuing

Active

Response queue

Done Todo Done Todo Active Active

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SLIDE 41

Next queue Currently queued

Fuzzy time - I/O queuing

Active

Response queue

Done Done Active Active

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SLIDE 42

Fermata

  • Time and web browsers
  • Mitigating attacks
  • A trusted browser
  • A (less) trusted browser
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SLIDE 43

Fermata - Why adapt fuzzy time?

  • Degrade clocks

○ Slow down attacks

  • Verifiability
  • Browsers are uniquely well suited
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SLIDE 44

Fermata - Fuzzy time for browsers

  • Adapt the VAX fuzzy time model to JS etc!
  • Put all I/O operations into queues
  • Make all the explicit clocks fuzzy
  • Prove everything falls into a fuzzy time defense

B u t w i t h J a v a S c r i p t !

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SLIDE 45

Fermata - Fuzzy time for browsers

  • Adapt the VAX fuzzy time model to JS etc!
  • Put all I/O operations into queues
  • Make all the explicit clocks fuzzy
  • Prove everything falls into a fuzzy time defense
  • Change all DOM accesses to be asynchronous!

B u t w i t h J a v a S c r i p t !

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SLIDE 46

Fuzzyfox

Rationale and design

  • Time and web browsers
  • Mitigating attacks
  • A trusted browser
  • A (less) trusted browser
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SLIDE 47

Why we didn’t build Fermata

1. We didn’t know if it would work 2. We didn’t know what to start with 3. We want to push mitigations to real browsers

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SLIDE 48

Fuzzyfox

  • Patch set on trunk Mozilla Firefox
  • Supports multiple clock granularities

○ Tested 0.5ms to 100ms

  • Fully fuzzes explicit clocks
  • Breaks main thread into ‘ticks’
  • Delays outgoing HTTP request start
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SLIDE 49

Next queue Current queue

Fuzzyfox - Main thread queuing

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SLIDE 50

Next queue Current queue

Fuzzyfox - Main thread queuing

Done Done Active Todo Todo Todo Todo

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SLIDE 51

Next queue Current queue

Fuzzyfox - Main thread queuing

Done Done Active Todo Todo Todo Todo Todo

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SLIDE 52

Next queue Current queue

Fuzzyfox - Main thread queuing

Done Done Active Todo Todo Todo Todo Todo

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SLIDE 53

Next queue Current queue

Fuzzyfox - Main thread queuing

Done Done Active Todo Todo Todo Todo Todo Pause

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SLIDE 54

Next queue Current queue

Fuzzyfox - Main thread queuing

Done Done Active Todo Todo Todo Todo Todo Pause

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SLIDE 55

Current queue

Fuzzyfox - Main thread queuing

Done Done Active Todo Todo Todo Todo Todo Pause

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SLIDE 56

Current queue

Fuzzyfox - Main thread queuing

Done Done Active Todo Todo Todo Todo Pause Done

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SLIDE 57

Current queue

Fuzzyfox - Main thread queuing

Done Done Active Todo Todo Todo Todo Pause Done Done

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SLIDE 58

Current queue

Fuzzyfox - Main thread queuing

Done Done Todo Todo Todo Todo Pause Done Done Done

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SLIDE 59

Current queue

Fuzzyfox - Main thread queuing

Done Done Todo Todo Todo Todo Pause Done Done Done Pause

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SLIDE 60

Current queue

Fuzzyfox - Main thread queuing

Done Done Todo Todo Todo Pause Done Done Done Pause Active

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SLIDE 61

Current queue

Fuzzyfox - Main thread queuing

Done Done Todo Todo Todo Pause Done Done Done Pause Active Done

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SLIDE 62

Queue 3 Queue 2 Queue 1

Fuzzyfox - Main thread queuing

Done Done Todo Todo Todo Done Done Done Active Done Pause Pause

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SLIDE 63

Current queue

Fuzzyfox - Main thread queuing

Done Todo Done Done Done Active Done

Epoch

Todo Pause Done Todo Pause

Epoch Epoch

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SLIDE 64

Current queue

Fuzzyfox - Main thread queuing

Done Todo Done Done Done Active Done

Epoch

Todo Pause Done Todo Pause

Epoch Epoch

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Current queue

Fuzzyfox - Main thread queuing

Done Todo Done Done Done Active Done

Epoch

Todo Pause Done Todo Pause

Epoch Epoch

  • Sleep
  • Update clocks
  • Flush queues
  • Schedule next pause
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SLIDE 66

Fuzzyfox

Effectiveness

  • Time and web browsers
  • Mitigating attacks
  • A trusted browser
  • A (less) trusted browser
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SLIDE 67

Fuzzyfox - Effectiveness - Explicit - performance.now()

Firefox Fuzzyfox

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SLIDE 68

Fuzzyfox - Effectiveness - Implicit - WebVTT clock

Firefox Fuzzyfox

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SLIDE 69

Fuzzyfox

Performance

  • Time and web browsers
  • Mitigating attacks
  • A trusted browser
  • A (less) trusted browser
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SLIDE 70

Fuzzyfox - Performance

  • “Micro” performance

○ Synthetic microbenchmark page load times

  • “Macro” performance

○ Real website load times

  • Interactivity

○ User study

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SLIDE 71

Fuzzyfox - Performance

  • “Micro” performance

○ Synthetic microbenchmark page load times

  • “Macro” performance

○ Real website load times

  • Interactivity

○ User study

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Fuzzyfox - Performance - Micro benchmarks

  • Page load times

○ As reported by onload()

  • Measured effects of

○ Sequential resource loads ○ Parallel resource loads

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SLIDE 73

Fuzzyfox - Performance - Sequential loads

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SLIDE 74

Fuzzyfox - Performance vs Tor Browser

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SLIDE 75

Takeaways

  • Time and web browsers
  • Mitigating attacks
  • A trusted browser
  • A (less) trusted browser
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SLIDE 76

Timing attacks

Rounding clocks doesn’t work

  • Time and web browsers
  • Mitigating attacks
  • A trusted browser
  • A (less) trusted browser
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SLIDE 77

Fuzzy time

Secure operating systems tech

  • Time and web browsers
  • Mitigating attacks
  • A trusted browser
  • A (less) trusted browser
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SLIDE 78

Fermata

A different design for the browser

  • Time and web browsers
  • Mitigating attacks
  • A trusted browser
  • A (less) trusted browser
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SLIDE 79

Fuzzyfox

Defenses that can work and that we can deploy

  • Time and web browsers
  • Mitigating attacks
  • A trusted browser
  • A (less) trusted browser
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SLIDE 80

Takeaways

  • Time and web browsers
  • Mitigating attacks
  • A trusted browser
  • A (less) trusted browser

This material is based upon work supported by the National Science Foundation and by a gift from Mozilla. We thank Kyle Huey, Patrick McManus, Eric Rescorla, and Martin Thomson at Mozilla for helpful discussions about this work, and for sharing their insights with us about Firefox internals.

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Fuzzyfox - Effectiveness - Explicit - performance.now()

Firefox Fuzzyfox

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Fuzzyfox - Effectiveness - Implicit - WebVTT clock

Firefox Fuzzyfox

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SLIDE 83

Performance - Micro benchmarks - Sequential loads

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Performance - Micro benchmarks - Tor Browser

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Performance - Load times* - Google search