Often touted as the next computational paradigm, many race to develop the first large-scale quantum computer. Google’s recent announcement that they achieved quantum supremacy — the ability for a quantum computer to do something a classical computer cannot — highlights concerns on whether we are prepared for a post-quantum world, one in which widely deployed cryptographic algorithms are broken. But how advanced are quantum computers really, and should we be worried about their impact on distributed ledger technologies? Join Atul Luykx, Head of Cryptography at Hedera Hashgraph, to learn how quantum computing is impacting cryptography and its applications. In this webinar, you’ll learn: - What happens when cryptography is broken? - How quantum computing breaks cryptography? - What can be done to avoid quantum attacks? - Hedera Hashgraph’s approach on quantum resistance in its consensus algorithm and public ledger. - Updates on the latest post-quantum cryptography developments

1. THE TRUST LAYER OF THE INTERNET

2. Quantum computing
and cryptography
HeadofCryptography
AtulLuykx
Warning: Inthis presentation, Crypto = Cryptography

4. Applications of
Quantum Computing

5. Scott Aaronson, “The Limits of
Quantum Computers,” Scientific
American, 2008
“… [quantum computers] would provide
dramatic speedups for a few specific
problems… For other problems, however—
such as playing chess, scheduling airline
flights and proving theorems—evidence now
strongly suggests that quantum computers
would suffer from many of the same
algorithmic limitations as today’s classical
computers.”

6. The Exception:
Cryptography
The Exception:
Cryptography

8. Introduction
• Head of Cryptography at Hedera
• Research Scientist at Visa Research
• Post-doc at KU Leuven and UC Davis
• PhD at KU Leuven

9. Case Study: Bitcoin transaction
Unlock Phone1.
2. Prepare Transaction
3. Send to blockchain

10. Case Study: Bitcoin transaction
Unlock Phone1.
2. Prepare Transaction
3. Send to blockchain

11. Secret-Key Cryptography
Aka symmetric-key crypto
• Example: AES (Advanced Encryption Standard)
• Impact of quantum computing: negligible,
assuming you switch to a larger key size
= 1011
Attempt Success?
0000
0001
0010
0011
0100
0101
…
N
N
N
N
N
N
…
Classical
Quantum
Grover’s algorithm
2k
2(k/2)
AES128
k-bit key
2128
264
AES256 2256
2128

12. Step 3: Sending to the blockchain
Unlock Phone1.
2. Prepare Transaction
3. Send to blockchain nonce
• Proof-of-work puzzle
constructed with hash functions
• Example: SHA-256

13. Cryptographic Hash functions
• Best known method of solving proof-of-work puzzle:
brute-force
• Grover’s algorithm
• Impact: negligible, increase hash function output,
increase difficulty

14. Preparing a Bitcoin Transaction
Unlock Phone1.
2. Prepare Transaction
3. Send to blockchain
From: you
To: friend
Amount: 1 BTC
…
Digital Signature
Purpose: ensures
transaction is authorized by
sender

15. Digital signature
• Type of public-key cryptography
• Example: RSA 3084, ECDSA
• Vulnerable to quantum computers --- ability
to recover keys using Shor’s algorithm
From: you
To: friend
Amount: 1 BTC
…
Valid/Invalid
Public Key
(ID)

16. Flame Malware
• Discovered in 2012
• Used for espionage
• Forged a Microsoft certificate to gain
access to systems
• Found a new cryptographic attack against
an algorithm which was widely known by
academics to be broken (MD5)
• Estimated that the malware was active for
as many as 5 years before its discovery
• Powerful attack: undetected, widely
applicable

17. Summary of
Impact• Secret key cryptography: increase the key length
• Hash functions: increase output size
• Digital signatures, public key cryptography --- need entirely different
algorithms

18. Next steps
• How much time do we have?
• What can we do about the attacks against public key crypto?

19. How much time do we have
• Current quantum computers < 100
qubits
• Qubits are noisy --- require error
correction to operate reliably
• Best attacks need 1000’s of logical
qubits
• With error correction, up to 100 000’s
• Estimates range from 200 qubits to
0.5 million qubits in 10 years

20. What solutions are there?
• Significant amount of
research on post-quantum
crypto
• Lattices
• Hash functions
• Code-based
• Multivariate
• NIST competition
Image source: Nick Matthewson’s talk at the Second PQC
Standardization Conference

21. Conclusions
• Wait and see
• Await standardization
• Vetting of security of algorithms
• But pay attention! Can’t just ignore crypto
• Need to remain crypto-agile: ability to switch algorithms quickly if necessary

22. Further reading
Scott Aaron, “The Limits of Quantum Computers”, Scientific American,
2008
http://www.cs.virginia.edu/~robins/The_Limits_of_Quantum_Computers.pdf
Ronald de Wolf, “The Potential Impact of Quantum Computers on Society”,
https://arxiv.org/pdf/1712.05380.pdf
NIST Post-Quantum Cryptography, https://csrc.nist.gov/Projects/Post-
Quantum-Cryptography
Cloudflare Blog on Post-Quantum crypto,
https://blog.cloudflare.com/towards-post-quantum-cryptography-in-tls/
How to factor 2048 bit RSA integers in 8 hours using 20 million noisy
qubits, https://arxiv.org/abs/1905.09749
Quantum attacks on Bitcoin, and how to protect against them,
https://arxiv.org/pdf/1710.10377.pdf