**Quantum computing is the use of quantum phenomena such as superposition and entanglement to perform computation. Which of the following is most vulnerable to quantum computing?**

A. Stream cipher

B. Symmetric encryption

C. Public key infrastructure

D. Lattice-based cryptosystem

**Kindly be reminded that the suggested answer is for your reference only. It doesn’t matter whether you have the right or wrong answer. What really matters is your reasoning process and justifications.**

My suggested answer is C. Public key infrastructure.

Quantum computers provide **no additional advantages** over classical computers in terms of computability, but in theory, they enable the design of **novel algorithms** that have significantly lower time complexities in specific areas than known classical algorithms. For example, **Shor’s algorithm** solves **Integer factorization** or the **discrete logarithm** problem, which endangers most public-key ciphers or the public key infrastructure.

# Symmetric Encryption

Symmetric encryption relies on bit state alternation (substitution and transposition), instead of mathematical computation like Integer factorization or discrete logarithm. So, quantum computers cause a limited impact upon symmetric ciphers. The threat can be mitigated by using longer keys.

# Stream Cipher

Stream ciphers are symmetric ciphers.

# Lattice-based cryptography

Lattice-based cryptography is the generic term for constructions of cryptographic primitives that involve lattices, either in the construction itself or in the security proof. Lattice-based constructions are currently important candidates for post-quantum cryptography. Unlike more widely used and known public-key schemes such as the RSA, Diffie-Hellman or elliptic-curve cryptosystems, which could, theoretically, be easily attacked by a quantum computer, some lattice-based constructions appear to be

resistantto attack by both classical and quantum computers.Source: Wikipedia

# Reference

- Quantum computingen.wikipedia.org/…ki/Quantum_cryptography
- Quantum cryptography (Wikipedia)
- Quantum cryptography definition
- Quantum Cryptography vs Post-Quantum Cryptography
- New Encryption System Protects Data from Quantum Computers
- Report on Post-Quantum Cryptography (NISTIR 8105)
- Post-Quantum Cryptography Standardization
- Quantum Encryption – A Means to Perfect Security?
- Quantum Cryptography Demystified: How It Works in Plain Language

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**量子計算(quantum computing)是利用諸如疊加(superposition)和糾纏(entanglement)之類的量子現象來執行計算。 以下哪項最容易受到量子計算的影響？**

A. 流密碼 (Stream cipher)

B. 對稱加密 (Symmetric encryption)

C. 公鑰基礎設施 (Public key infrastructure)

D. 基於格子的密碼系統 (Lattice-based cryptosystem)

A

A