Public Blockchain technology like Ethereum is gaining interest and growing use case among startup and fintechs. Apart from scalability issues which are going to be solved with new consensus and mining techniques (Ethereum Metropolis and Bitcoin SegWit2x with Lightning network), the privacy of transactions is still an issue which is not yet fully addressed. Due to the public nature of Ethereum, many businesses are reluctant to deploy Smart-contract or Dapps solutions for fear of exposing confidential or sensitive information. The use of zk-SNARKs (zk-SNARK stands for “Zero-Knowledge Succinct Non-Interactive Argument of Knowledge”) essentially solves this blocker. Moreover, the next Ethereum Improvement Proposal called 'Byzantium' includes zk-SNARKS. zk-SNARKs allows verification of the correctness of computations, without a verifier having to execute those computations or even learn what was actually executed. Using zk-SNARKs, a verifier can confirm that a computation happened correctly, with ‘zero-knowledge’ of the computation itself. During this talk, we present a brief overview of cryptography and the theory around the zero-knowledge proof algorithm. Then we showcase the benefits of zk-SNARKS and other privacy-preserving techniques (like zcash) on the public blockchain ecosystem.

1. Privacy-preserving techniques using zero
knowledge proof in public Ethereum
3 November 2017
ELCA Informatique SA
Nagib Aouini, Head of Cyber Security Services
Dr Sonia Bogos, Cryptography Engineer
Jorge Alvarado, Lead Blockchain architect, ELCA 1

2. Agenda
― Why Privacy is important in blockchain ?
― Theory and concept around Zero Knowledge proof
― Application of zk-SNARKs in public Ethereum Blockchain
― Q & A
1
2
3
4

3. Importance of
privacy
3
• Essential human right
• Allow people exercise unique moral
choices
• Enable our societies evolved around is
healthy, and makes it more resilient and
more humane

4. ©copyright 2017
Why privacy matters
Privacy-preserving techniques using zero knowledge proof in public Ethereum - Nov 3 - BAT38 4

5. Once data is
embedded in the
blockchain it
cannot be altered
•
•
•

6. Do you think
Bitcoin is still
anonymous ?
• Wallet address re-use, linking your transactions
together into a single profile.
• IP address re-use.
• Combining inputs from multiple transactions,
• Using mobile wallet, effectively revealing to a third
party your full set of addresses.

7. Following a bitcoin
transaction

8. 8

9. ©copyright 2017
How to make private transaction in the blockchain
Privacy-preserving techniques using zero knowledge proof in public Ethereum - Nov 3 - BAT38 9

10. ©copyright 2017
Application of Zero Knowledge Proof
Privacy-preserving techniques using zero knowledge proof in public Ethereum - Nov 3 - BAT38 10
Source :

11. In a Zero-knowledge (ZK) proof we have
2 participants:
• Prover - Peggy
• Verifier - Victor
The prover wants to convince the
verifier that a statement is true without
leaking any extra information.
E.g. the prover wants to convince the
verifier that he has a secret without
revealing it.
Privacy-preserving techniques using zero knowledge proof in public Ethereum - Nov 3 - BAT3811
Zero-knowledge proof

12. ©copyright 2017
Zero-knowledge proof
Privacy-preserving techniques using zero knowledge proof in public Ethereum - Nov 3 - BAT38 12

13. Properties of ZK proofs:
• Termination: the protocol finishes
after a number of steps.
• Completeness: if the statement is
true then the verifier will be
convinced of this at the end of the
protocol.
• Soundness: if the statement is false
then it is unlikely that the verifier will
be fooled.
• Zero-knowledge: at the end of the
protocol no sensitive information is
leaked to the verifier.
Privacy-preserving techniques using zero knowledge proof in public Ethereum - Nov 3 - BAT3813
Zero-knowledge proof

14. ©copyright 2017
zkSNARK
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Zero-knowledge Succinct Non-interactive ARguments of Knowledge
Zero-knowledge: proving existence of a secret without revealing it
Succinct: the communication volume is small
Non-interactive: no interaction
Arguments of Knowledge: proving that one knows the secret

15. ©copyright 2017
Non-interactive Zero-knowledge proof (NIZK)
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Peggy Victor
Common Reference String
Source: https://thenounproject.com
Secret s
Proof p
Verify proof p

16. ©copyright 2017
Common Reference String (CRS)
Privacy-preserving techniques using zero knowledge proof in public Ethereum - Nov 3 - BAT38 16
Initial parameters Trusted Setup
Common Reference String
Destroy the
parameters !

17. ©copyright 2017
Pairing on elliptic curves
Privacy-preserving techniques using zero knowledge proof in public Ethereum - Nov 3 - BAT38 17Source: https://desmos.com/calculator, https://en.wikipedia.org/wiki/Swiss_passport
𝐸 𝑎,𝑏 = 𝑂 ∪ { 𝑥, 𝑦 ; 𝑦2
= 𝑥3
+ 𝑎𝑥 + 𝑏}
RSA (bit length) EC (bit length) Security level
1248 160 80
2048 224 112
Pairing: mathematical tool used to instantiate a NIZK
Elliptic curve:
Efficiency
Used by

18. Homomorphic encryption allows to
perform operations on sensitive data
while keeping it encrypted.
Use case: secure cloud computing
Privacy-preserving techniques using zero knowledge proof in public Ethereum - Nov 3 - BAT3818
𝐸𝑛𝑐 𝑚 + 𝐸𝑛𝑐 𝑛 = 𝐸𝑛𝑐(𝑚 + 𝑛)
Homomorphic evaluation/
encryption

19. ©copyright ELCA 2017
Agenda
― Privacy in Ethereum
― Byzantium
― Zk-SNARKs
― Demo
― ZoKrates
― Conclusions
1
2
3
4
5
6
19

20. ©copyright ELCA 2017
Self-service Business
Oriented
Ethereum: public
but private but
public…
20
https://pixabay.com/en/replacement-lamp-lighting-951781/

21. ©copyright ELCA 2017
Self-service Business
Oriented
Byzantium what?
21
https://pixabay.com/en/replacement-lamp-lighting-951781/

22. ©copyright ELCA 2017
Self-service Business
Oriented
zk-SNARKs what?
22
https://pixabay.com/en/replacement-lamp-lighting-951781/

23. ©copyright ELCA 2017 23
?
?
?
?
Reference: https://www.reddit.com/r/ethereum/comments/712idt/ethereum_testnet_just_verified_a_zcash_transaction/
TEST Contract
Library: Pairing
Pre-compiled EC
operations
How does it work?

24. ©copyright ELCA 2017 24
Demo…

25. ©copyright ELCA 2017
Self-service Business
Oriented
ZoKrates… what?
25
https://pixabay.com/en/replacement-lamp-lighting-951781/

26. ©copyright ELCA 2017 26
ZoKrates
“… ZoKrates allows information to be obscured off the main ethereum blockchain and then
uploaded into a smart contract the network can still verify, all without exposing contract
information.”
It is another type of ethereum smart contract. A custom version of the self-executing code that runs
on top of the network, the tool serves as a way to transfer a zk-SNARKs operation onto the
blockchain and to verify that that information is valid.

27. ©copyright ELCA 2017
Conclusions
― Privacy is the holy-grail of public blockchains
― zk-SNARKs allows to verify something without knowing the details
― Byzantium fork on Ethereum brings new functionality to facilitate the
verifiability of zk-SNARKS
― zk-SNARKs is difficult to grasp and even more difficult to code and automate
― More tooling is needed and ZoKrates attempts to fill the gap
27

28. Innovations @
ELCA
ELCA is working on innovation projects which aim to
cover the following domains:
• Cloud Security and Searchable Encryption in the
cloud
• ChatBot and Natural Language processing
• BigData
• Blockchain

29. ©copyright 2017
ELCA expertise
Digital & Business
Transformation
Complexity
Reduction
Modernization
Automation
& Standartisation
Time to Market
& Agility
Alignement Business
& IT
Security …
MARKET CHALLENGES
PROJEKT ERFAHRUNG
Consulting
Software
Engineering
Technology
Integration
Application &
Cloud Management
BRANCHEN ERFAHRUNG
Financial
Services
Health &
Pension
Public
Administration
Defense &
Cybersecurity
Transportation &
Logistics
Retail & Other
Industries
(ex. Intern. Org,
Energy etc.)
ANGESAGTE THEMEN
IT Business
Consulting
ECM Enterprise
Content
Management
CIM Customer
Interaction
Management
Big Data &
Analytics
SaaS Service
& Operations
Architecture
Privacy-preserving techniques using zero knowledge proof in public Ethereum - Nov 3 - BAT38 29

30. ©copyright 2017
Blockchain team
Privacy-preserving techniques using zero knowledge proof in public Ethereum - Nov 3 - BAT38 30
Nagib Aouini : nagib.aouini@elca.ch
Blockchain Technical Advisor /
Strategist
Jorge A.
Ethereum Expert
Hyperledger
Smart Contract
Cloud Architect
Laurent P
Blockchain Java
Hyperledger
Smart Contract
Architect
Reto F.
Security Architect
Blockchain Expert
Zurich
Head of Division / Senior
Consultant
Blockchain evangelist
> 10 senior manager
Sébastien P
Lead Architect
Dev Team
Smart contract
> 10 engineers
– Blockchain
– Team
– Industry
– Business
expert
Financial
– Industry
– Business
expert
Insurance
– Industry
– Business
expert
– Public
sector
– Industry
– Business
expert
Healthcare
Dedicated skilled Blockchain experts

31. ©copyright 2017
• Discuss Blockchain technology
• Explore customer business
model
• Show Blockchain Application
demo
• Understand Blockchain
concepts & elements
• Hands on with
Blockchain on Ethereum /
Hyperledger / Others
• Standard demo customization
• Define business challenge
• Agile iterations incrementally
build project functionality
• Enterprise integration
• Provide Blockchain Dev expert
and consulting services
Élaboration Construction
How ELCA can help on Blockchain technology
Blockchain Hands-
on
Experience
Blockchain
Provide Expertise
and First Project
Privacy-preserving techniques using zero knowledge proof in public Ethereum - Nov 3 - BAT38 31

32. Mr Nagib Aouini Mr Jorge Alvaradp
Head of Cyber Security Lead Blockchain Architect
Nagib.aouini@elca.ch Jorge.alvarado@elca.ch
Tel : 021 613 2136 Tel : 021 613 2111
Confidential do not distribute 32
Dr Sonia Bogos
Crypography Engineer
Sonia.bogos@elca.ch
Tel : 021 613 2111