Yodel: Strong Metadata Security for Real-Time Voice Calls David - - PowerPoint PPT Presentation

Yodel: Strong Metadata Security for Real-Time Voice Calls

David Lazar, Yossi Gilad, Nickolai Zeldovich

• 1

MIT CSAIL

Metadata is data that can’t be encrypted

2

Chat Service src/dst msg size sent time

What can you learn from metadata?

3

Dan Guardian Erin NYT Alice Bob Carol Fred

Passive Network Adversary

Huawei Executive Saudi Dissident

Security goal: hide who is talking to whom

4

Active Network Adversary

?

?

?

Passive Network Adversary

Performance goal: sub-second latency

5

× millions

< 1s

Prior work doesn’t meet goals

Passive attacks Active attacks Performance Pung

[OSDI 2016]

Karaoke

[OSDI 2018]

Herd

[SIGCOMM 2015] Differential privacy 7s Trusted server

6

Contributions

Yodel: the first system for real-time voice calls with

• Strong protection against passive & active attacks
• Distributed trust (any-trust or fractional trust)
• Sub-second latency for 5M users with 100 servers

Two key insights

• Self-healing circuits & Guarded circuit exchange

7

Mixnets hide who sent which message

8

Server 1 Server 2 Server 3

x y

y x y

x y

x Onion-encrypted Message

9

Server 1 Server 2 Server 3

Mixing is expensive: public key

• peration for each message at every hop

gx gx gx gx gx gx gx gx gx

10

Yodel’s mixnet: send public key onions to setup symmetric key circuits

Circuit setup onion

11

Server 1 Server 2 Server 3

Circuit messaging

⨁ ⨁ ⨁ ⨁ ⨁ ⨁ ⨁ ⨁ ⨁

= circuit (symmetric key) onion

12

Server 1 Server 2 Server 3

Challenge: attacker has many chances to learn shuffle of honest server!

! !

Yodel’s key insight: self-healing circuits

13

Server 1 Server 2 Server 3

3

Users connect to circuits

14

Yodel round steps

1

Users establish circuits = random string x y

2

Users exchange circuits x y

External Messaging Service

4

Users send voice packets

Mixnet

Evaluation

Does Yodel achieve low latency for large numbers of users? Does Yodel offer acceptable voice quality?

15

Yodel achieves sub-second latency for 5M users

16

0.6s 0.8s 1.0s 1.2s 1.4s 1.6s 2M 4M 6M 8M Voice packet latency Number of users 100 servers, US & EU

17

• Joanna and I had a short conversation over Yodel, with

5M other “users” actively using the system

• She ran Yodel over her laptop speakers and recorded the

convo with her phone

• (phone records her voice directly)
• Some latency (~1s) is due to us waiting to not talk over

each other

Yodel achieves acceptable voice quality

18

Pre-recorded demo

Conclusion

Yodel: the first system for real-time voice calls with

• Strong metadata privacy (against passive & active attacks)
• Distributed trust (any-trust or fractional trust)
• Sub-second latency for 5M users with 100 servers

Full paper and code coming soon:

• vuvuzela.io
• davidlazar.org