AES-256 and Quantum Computing: Only Half the Story
From a symmetric cryptography standpoint, AES-256 is a robust choice in a post-quantum world. Even in the presence of a large-scale quantum computer, Grover’s algorithm only provides a quadratic speedup, meaning AES-256 still offers an effective security level that is widely considered acceptable.
However, real-world security protocols are not built on AES alone. Protocols such as IPsec, TLS, SSH, and 802.1X may encrypt data with AES-256, but the AES keys themselves are typically established and authenticated using classical asymmetric cryptography: RSA, Diffie–Hellman (DH), Elliptic-Curve Diffie–Hellman (ECDH), or elliptic-curve signatures (ECDSA, EdDSA).
These asymmetric algorithms are exactly the ones that are vulnerable to quantum attacks such as Shor’s algorithm.
The Weakest Link Problem
In practice, relying on AES-256 while keeping classical public-key mechanisms unchanged is like installing an extremely strong lock on your front door, but leaving the key under the doormat. The lock itself is solid, but the overall security is determined by the weakest link — in this case, the key management.
If an attacker can break the classical key exchange or signature scheme:
- They can recover session keys and retrospectively decrypt recorded traffic (the “store now, decrypt later” threat model).
- They can impersonate legitimate entities by forging signatures or undermining authentication.
In both cases, the fact that AES-256 is used for bulk encryption does not prevent a compromise of confidentiality or integrity.
What Does “Quantum-Safe” Really Mean?
A system cannot seriously be described as quantum-safe if any critical cryptographic primitive it relies on is known to be vulnerable to large-scale quantum computers.
To achieve meaningful quantum resistance, systems must address:
- Confidentiality: Not only by using strong symmetric algorithms (e.g. AES-256), but also by ensuring that key exchange mechanisms are resistant to quantum attacks.
- Integrity and authenticity: By using digital signature schemes that remain secure in a post-quantum scenario.
In other words, both the encryption and the key-exchange/signature mechanisms must be based on post-quantum (PQ) algorithms, or on well-designed hybrid schemes that include them.
The Role of Hybrid Schemes
During the transition to post-quantum cryptography, many standards bodies and experts recommend hybrid approaches:
- Combine a classical algorithm (e.g. ECDHE, RSA, ECDSA) with a post-quantum key encapsulation mechanism (KEM) or signature.
- The security of the overall scheme then relies on both components: even if one is later broken, the other still provides protection.
This approach has several advantages:
- It maintains interoperability with existing infrastructures.
- It allows organizations to adopt PQ algorithms gradually, while standards and implementations mature.
- It reduces the risk associated with potential weaknesses discovered in new PQ constructions.
How We Approach Post-Quantum Security at Ekinops
At Ekinops, we take post-quantum security very seriously. For us, being “quantum-safe” is not a marketing label; it is an architectural requirement.
Our approach is holistic:
- We phase out classical-only asymmetric primitives in favor of schemes that incorporate post-quantum algorithms selected by recognized authorities.
- We deploy hybrid key exchange and signature mechanisms, combining classical and post-quantum methods, in line with recommendations from NIST, ANSI, and other standardization bodies.
- We consider both data in motion (e.g. IPsec, TLS-based management, control and user planes) and the broader lifecycle of cryptographic materials, including authentication and key management.
The objective is clear: avoid a situation where traffic appears well protected because AES-256 is used, while in reality a quantum-capable adversary could recover keys or forge identities by attacking the underlying classical public-key cryptography.
Conclusion
AES-256 is a necessary component of a quantum-resilient design, but it is not sufficient. True quantum-safe security requires rethinking the entire cryptographic stack: key exchange, authentication, and encryption must all be robust against quantum adversaries.
Quantum-safe is not a checkbox next to “AES-256 supported.” It is an end-to-end design principle — one that we are actively implementing at Ekinops through the adoption of post-quantum and hybrid cryptography across our solutions.
Amine ISMAIL Ph.D
VP Technology access at Ekinops
