It has been established that quantum algorithms can solve several key cryptographic problems more efficiently than classical computers. As progress continues in the field of quantum computing it is important to understand the risks they pose to deployed cryptographic systems. Here we focus on one of these risks - quantum key-recovery attacks against ideal ciphers. Specifically, we seek to model the risk posed by an economically motivated quantum attacker who will choose to run a quantum key-recovery attack against an ideal cipher if the cost to recover the secret key is less than the value of the information at the time when the key-recovery attack is complete. In our analysis we introduce the concept of a quantum cipher circuit year to measure the cost of a quantum attack. This concept can be used to model the inherent tradeoff between the total time to run a quantum key recovery attack and the total work required to run said attack. Our model incorporates the time value of the encrypted information to predict whether any time/work tradeoff results in a key-recovery attack with positive utility for the attacker. We make these predictions under various projections of advances in quantum computing. We use these predictions to make recommendations for the future use and deployment of symmetric key ciphers to secure information against these quantum key-recovery attacks. We argue that, even with optimistic predictions for advances in quantum computing, 128 bit keys (as used in common cipher implementations like AES-128) provide adequate security against quantum attacks in almost all use cases.
It has been established that quantum algorithms can solve several key cryptographic problems more efficiently than classical computers. As progress continues in the field of quantum computing it is important to understand the risks they pose to deployed cryptographic systems. Here we focus on one of these risks - quantum key-recovery attacks against ideal ciphers. Specifically, we seek to model the risk posed by an economically motivated quantum attacker who will choose to run a quantum key-recovery attack against an ideal cipher if the cost to recover the secret key is less than the value of the information at the time when the key-recovery attack is complete. In our analysis we introduce the concept of a quantum cipher circuit year to measure the cost of a quantum attack. This concept can be used to model the inherent tradeoff between the total time to run a quantum key recovery attack and the total work required to run said attack. Our model incorporates the time value of the encrypted information to predict whether any time/work tradeoff results in a key-recovery attack with positive utility for the attacker. We make these predictions under various projections of advances in quantum computing. We use these predictions to make recommendations for the future use and deployment of symmetric key ciphers to secure information against these quantum key-recovery attacks. We argue that, even with optimistic predictions for advances in quantum computing, 128 bit keys (as used in common cipher implementations like AES-128) provide adequate security against quantum attacks in almost all use cases.
The development of quantum computers represents an important advancement in computing, using quantum mechanics to address problems that were previously difficult to solve. This technological advancement poses a challenge for cryptographic systems. While some methods are known to be vulnerable, the impact of quantum computing on symmetric cryptography has received less research attention, largely because the common advice is to simply double the key size. This paper explores how quantum computing affects symmetric cryptography, focusing on block cipher-based cryptography. It surveys existing literature on the quantum resilience of symmetric cryptographic primitives based on block ciphers and their security in various scenarios. Not all symmetric cryptographic functionalities are quantum-secure, and their security depends on the specific adversary model being considered. We provide an overview of the research conducted and pinpoint areas where further investigation is needed.
The development of post-quantum cryptography requires cryptographic primitives that remain secure against quantum adversaries. Quantum key-recovery attacks constitute a fundamental class of quantum cryptanalytic techniques, and the resistance of a cryptosystem to such attacks serves as an important indicator of its overall security. Since the Feistel structure is a core component in the design of many block ciphers, efficient quantum key-recovery attacks on Feistel ciphers provide valuable insights into evaluating and strengthening their security. In this paper, we propose an efficient generic quantum key-recovery attack on Feistel ciphers. Our attack integrates universal hash families with Simon's and Grover's algorithms to perform key-recovery. We rigorously analyze the correctness of the proposed attack and derive its time and quantum resource complexities. A comprehensive comparison with existing keyrecovery attacks shows that the proposed approach improves both quantum resource usage and dominant query complexity, and therefore yields a more efficient quantum key-recovery attack. Our work enhances the understanding of Feistel ciphers under quantum threats and informs the design of robust cryptosystems for the post-quantum era.
Quantum computing is a transformational technology once implemented, capable of addressing problems far beyond the capacity of classical computers. But this progress is also a real challenge to the core of today's modern security. Traditional cryptographic algorithms, such as those based on RSA, ECC, and Diffie-Hellman key exchange, are based on the computational hardness of problems such as prime factorization and discrete logarithms that quantum algorithms solve in polynomial time. As a particular research interesting example, with Shor's Algorithm one can factorize large numbers efficiently, rendering insecure the majority of public key cryptosystems used nowadays. This urgently demands a reevaluation of existing encryption schemes in the context of a post-quantum world. In this paper, we take a closer look at the threats that quantum computers pose to classical security infrastructure including encryption scheme and explore the impact that quantum computation can have on current cryptographic schemes. It calculates the cost in terms of symmetric and asymmetric security, accounting for effects of both Shor's and Grover's algorithms. Symmetric key systems such as AES are also harder hit—Grover's algorithm can give only a quadratic speedup here—but they do need to double key sizes for a sufficient level of post-quantum security. In reaction to those threats, the paper investigates nextgeneration post-quantum cryptographic (PQC) solutions resistant to quantum cryptanalysis. Lattice-based cryptosystems, hash-based signature schemes, multivariate polynomial systems, and code-based cryptosystems are some of the candidates that are being considered in international standardization work, including especially at NIST. In this paper, we compare those alternatives for security, performance, scalability, and feasibility of implementation in real system. An important aspect of this contribution is a comparative study of traditional and post-quantum cryptographic protocols in the context of a number of cybersecurity applications, including secure communications, blockchain networks and IoT contexts. It also covers the quantum readiness timeline and transitional issues, such as backward compatibility, standardization lag and the associated increased computational overhead. Through a mitigated risk evaluation and cryptanalytic attack simulation based on quantum-inspired algorithms, this analysis emphasizes the need to prepare ourselves against quantum-induced security issues. It provides strategic guidance to organizations as they plan for the post-quantum future, stressing cryptographic agility, hybrid encryption models and real-time threat monitoring. Ultimately, the results of this work add to the worldwide conversation on establishing secure systems within the digital age of quantum computing and recommend proactive migration plans for the integrity, confidentiality, and trust one should have in the future cyber world.
Recent advances in cryptography aim to address threats posed by quantum computers. However, these advances have focused disproportionately on asymmetric schemes, while symmetric primitives like block ciphers have received less attention. The common assumption is that doubling block cipher key sizes provides adequate quantum resistance, but this oversimplifies the challenge. This paper provides a systematic examination of block cipher security in the quantum computing era. The paper first establishes a formal framework for understanding block cipher security, covering their mathematical foundations and essential security properties. Building on this foundation, we examine how quantum computing fundamentally challenges these security assumptions, going beyond the simple impact on key lengths. Our review of recent research reveals that quantum attacks can exploit structural vulnerabilities in block ciphers and their modes of operation, requiring more comprehensive defenses than key length adjustments alone. We analyze emerging approaches in quantum-resistant design and identify critical areas requiring further research to ensure block cipher security in a post-quantum world.
This paper investigates the potential impact of quantum computing on the security of currently deployed cryptographic algorithms. The core premise is that the advent of powerful quantum computers, leveraging algorithms like Shor's algorithm and Grover's algorithm, poses a significant threat to widely used public-key cryptosystems and symmetric-key algorithms. We present a theoretical analysis of several key algorithms – RSA, ECC, and AES – examining their vulnerabilities when subjected to quantum attacks. Specifically, we explore the exponential speedup offered by Shor's algorithm for factoring large numbers, the impact on the key size of ECC, and the Grover's algorithm's influence on symmetric key search. Our work highlights the urgency of transitioning to post-quantum cryptography standards to mitigate the risks posed by this technological advancement. The goal is to provide a comprehensive understanding of the landscape of quantum cryptanalysis and its implications for the future of secure communication.
Quantum computing is the study of computers that use quantum features
in calculations. For over 20 years, it has been known that if very
large, specialized quantum computers could be built, they could have a
devastating effect on asymmetric classical cryptographic algorithms
such as RSA and elliptic curve signatures and key exchange, as well as
(but in smaller scale) on symmetric cryptographic algorithms such as
block ciphers, MACs, and hash functions. There has already been a
great deal of study on how to create algorithms that will resist
large, specialized quantum computers, but so far, the properties of
those algorithms make them onerous to adopt before they are needed.
Small quantum computers are being built today, but it is still far
from clear when large, specialized quantum computers will be built
that can recover private or secret keys in classical algorithms at the
key sizes commonly used today. It is important to be able to predict
when large, specialized quantum computers usable for cryptanalysis
will be possible so that organization can change to post-quantum
cryptographic algorithms well before they are needed. This document
describes quantum computing, how it might be used to attack classical
cryptographic algorithms, and possibly how to predict when large,
specialized quantum computers will become feasible.