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), privacy on transaction is still an issue which is not yet fully addressed yet. Because of the public nature of a 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”) would essentially solve this dilemma (next EIP improvement of Ethereum called 'Byzantium' include zk SNARKS). The idea of zk-SNARKs is that they allow 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. We propose during this talk to have a brief presentation on cryptography and theory around zero-knowledge proof algorithm. Then we will try to showcase the benefits of zk-SNARKS and other privacy-preserving techniques (like zcash) on the public blockchain ecosystem.

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

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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
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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

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How to make a private transaction in the blockchain
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Application of Zero Knowledge Proof
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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

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Zero-knowledge proof
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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

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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

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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

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Common Reference String (CRS)
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Initial parameters Trusted Setup
Common Reference String
Destroy the
parameters !

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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

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?
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Reference: https://www.reddit.com/r/ethereum/comments/712idt/ethereum_testnet_just_verified_a_zcash_transaction/
TEST Contract
Library: Pairing
Pre-compiled EC
operations

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27. Innovations @
ELCA
ELCA is working on innovation projects wich aims to
cover the following domain(s)
• Cloud Security and Searchable Encryption in the
cloud
• ChatBot and Natural Language processing
• BigData
• Blockchain

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ELCA expertise
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Blockchain team
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expert
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How ELCA can help on Blockchain technology
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31. 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 31
Dr Sonia Bogos
Crypography Engineer
Sonia.bogos@elca.ch
Tel : 021 613 2111