7 reasons why classical encryption fails against quantum computers

Quantum computers are changing the rules of the game for network security. What is considered secure today could be cracked in minutes by a powerful quantum computer tomorrow. Yet many organizations still rely on classical encryption standards designed for an era without quantum threats. In this article, you will learn exactly why classical encryption fails against quantum computers and why post-quantum cryptography is no longer a luxury, but a necessity.

The quantum threat to modern network security

Classical encryption is built on mathematical problems that are practically unsolvable for traditional computers. Quantum computers work in a fundamentally different way: they use quantum bits that can occupy multiple states simultaneously, allowing certain calculations to run exponentially faster. This makes a large portion of current cryptographic standards vulnerable.

The threat is not hypothetical. Governments and major technology companies are investing globally in the development of powerful quantum systems. Organizations that take no action now risk having their sensitive data intercepted today and decrypted later once the technology becomes available. This is known as the “harvest now, decrypt later” principle. Explore our security solutions to understand how to protect your organization against this growing threat.

1: RSA keys are mathematically vulnerable to Shor

RSA has been the backbone of asymmetric encryption for decades. Its security rests on the fact that factoring large numbers into their prime components is practically impossible for classical computers. However, Shor’s algorithm, designed for quantum computers, solves this problem in polynomial time.

What does this mean in practice? A 2048-bit RSA key, which would take a classical computer millions of years to crack, could be compromised by a sufficiently powerful quantum computer in hours or even minutes. The longer the key, the more quantum bits are required, but the fundamental vulnerability remains.

RSA is used in virtually every secure connection: HTTPS, email encryption, and digital certificates. Organizations that depend on RSA to protect business-critical communications face a serious problem once quantum computers reach maturity.

2: ECC offers no better quantum resistance

Elliptic Curve Cryptography (ECC) is often presented as a more efficient alternative to RSA, offering shorter keys with comparable security. But ECC provides no protection against quantum attacks either. Shor’s algorithm is equally applicable to the discrete logarithm problem on which ECC is based.

This is a common misconception in the industry. Organizations that have switched to ECC under the assumption that it makes them future-proof face the same vulnerabilities as with RSA. The shorter key length even makes ECC faster to crack for a quantum system in some cases.

ECC is a good choice for classical environments due to its efficiency, but when it comes to protection against quantum threats, it offers no advantage over RSA. Both standards require replacement with post-quantum alternatives.

 

 

3: Symmetric keys are effectively halved

Symmetric encryption, such as AES, is less vulnerable than asymmetric methods, but it is certainly not immune. Grover’s algorithm, another quantum algorithm, can effectively halve the key length of symmetric encryption by executing an accelerated brute-force attack.

With Grover’s algorithm, an AES-128 key offers only the equivalent of 64 bits of security, which is considered insufficient for serious applications. AES-256 retains an effective strength of 128 bits, which is currently regarded as secure, but this requires organizations to actively migrate to longer keys.

Many systems still run on AES-128 or even older standards. This is a vulnerability that can be addressed right now, without waiting for full post-quantum cryptography implementations. Check which key lengths your infrastructure is using.

4: Key exchange is the weakest link

Even when the encryption itself is strong, the way keys are exchanged can undermine the entire security posture. Diffie-Hellman and ECDH, the most widely used key exchange protocols, are both vulnerable to Shor’s algorithm. A quantum attacker who intercepts the key exchange can reconstruct the shared key and decrypt all encrypted communications.

This also applies to stored communications. If an attacker captures encrypted traffic today and later breaks the key exchange once quantum computers become available, they will have access to all historical communications. This makes key exchange one of the most urgent components of any quantum security agenda.

Post-quantum key encapsulation mechanisms, such as those standardized by NIST, are designed to solve this problem. Implementing them should be a priority in any security strategy that accounts for the quantum threat.

5: Digital signatures lose their trustworthiness

Digital signatures are used to guarantee the authenticity and integrity of data, from software updates to legal documents and network certificates. They are based on the same asymmetric algorithms, RSA and ECC, that are vulnerable to quantum attacks.

An attacker with a powerful quantum computer can forge signatures that existing systems recognize as legitimate. This opens the door to man-in-the-middle attacks, the distribution of malicious software accepted as genuine, and the undermining of trust chains in PKI infrastructures.

The consequences are far-reaching: from compromised software updates in critical infrastructure to unreliable authentication in financial systems. Post-quantum signature algorithms are available and are already being tested and deployed by forward-thinking organizations.

6: VPN tunnels offer a false sense of security

VPN connections are widely used for secure communication over public networks. But a VPN is only as strong as the underlying cryptographic protocols. Most VPN implementations use TLS or IPsec with Diffie-Hellman key exchange and RSA or ECC certificates, all of which are vulnerable to quantum attacks.

This means organizations that rely on VPN tunnels to protect sensitive business communications may have a false sense of security. The tunnel is visible to an attacker who stores the traffic for later decryption.

The solution is not to abandon VPN, but to upgrade its cryptographic foundation. Encryption solutions built on post-quantum algorithms, or those operating at Layer 1 and Layer 2 of the OSI model, offer fundamentally stronger protection regardless of vulnerabilities in higher-level protocols.

7: Outdated protocols survive in legacy networks

Many organizations run systems that are years or even decades old. These legacy systems often use protocols that are already considered weak against classical threats, let alone quantum attacks. Examples include outdated TLS versions, SHA-1 hashing, and 3DES encryption.

The problem is that these systems are often not easy to update. They are integrated into operational technology, industrial control systems, or critical infrastructure where downtime is not acceptable. Yet they represent a serious risk: a single vulnerable node can compromise the security of the entire network.

A thorough inventory of all cryptographic protocols in the network infrastructure is the first step. Know which systems use which encryption, identify the vulnerabilities, and develop a migration strategy that accounts for operational continuity. Delay only increases the risk.

Quantum-safe security starts now

The transition to post-quantum cryptography is not a future project. It is a journey that must begin now, because the risks are already real and the migration timeline for complex network infrastructures is substantial. Organizations that wait until quantum computers go mainstream will be too late.

The steps are clear:

• Take inventory of all cryptographic protocols and key lengths in your infrastructure
• Identify which systems are most vulnerable to quantum attacks
• Prioritize key exchange and digital signatures as the first migration targets
• Consider Layer 1 and Layer 2 encryption as an additional layer of protection
• Develop a phased migration plan aligned with your systems’ lifecycle

How we help with quantum-safe network security

We understand that the transition to quantum-safe security is complex, especially in environments with critical infrastructure, legacy systems, or high availability requirements. Drawing on our expertise in physical network infrastructure and more than 20 years of experience in connectivity, we help organizations approach this transition in a structured and practical way.

Our security portfolio offers concrete solutions for the vulnerabilities described in this article:

• Quantum security: encryption solutions resistant to quantum attacks, including for existing network infrastructure
• Layer 1 and Layer 2 encryption: protection at the deepest levels of the OSI model, independent of vulnerable higher-level protocols
• Vendor-independent advice: we select the solution that fits your environment, not a preferred supplier
• End-to-end guidance: from inventory and risk analysis to implementation and management

Whether you work in a data center, healthcare facility, maritime environment, or critical infrastructure: we translate the quantum threat into a concrete approach tailored to your situation. Explore our security solutions or get in touch to discuss how we can make your network quantum-safe.