Quantum Resilience

The confidentiality of data is primarily secured by encrypting it.

While data at rest is encrypted with symmetric encryption algorithms, the encryption of data in transit relies on public key cryptosystems to exchange the symmetric session key which in turn is used to encrypt the transmitted data. 

Harvest now, decrypt later

The concept of “Harvest now, decrypt later” (HNDL) presents a substantial risk, particularly for sensitive data requiring confidentiality over extended periods, such as government communications, medical records, or intellectual property with long-term value.

The HNDL threat refers to the practice of adversaries gathering encrypted information with the intention of retaining it until future advancements in quantum computing may enable decryption.

Essentially, HNDL is the concept formalized by Mosca’s Theorem (see above, “X+Y > Q”) and constitutes a threat to confidentiality of sensitive data, as information intercepted today may become accessible to adversaries in the future.

Authentication and non‑repudiation is secured by enabling verifiable proof of identity and transaction, respectively, using cryptographic protocols. Authentication is achieved through mechanisms such as digital certificates, challenge–response protocols, and message authentication codes (MACs), which are often based on public key cryptographic protocols.

Non‑repudiation is primarily provided by digital signatures, which use public key cryptography to bind an identity to a specific message or transaction in a way that can be independently verified and cannot be denied later.

Trust now, forge later

The concept of “Trust now, forge later” (TNFL) describes the risk affecting digital signatures and non‑repudiation, where for example signatures that are trusted as valid today can be forged in the future once cryptographic algorithms are broken by quantum computers.

As a result, previously trusted records – such as software updates, contracts, certificates, identity credentials, audit logs, or blockchain transactions – lose their evidentiary value.

Any overlooked quantum-vulnerable login key may serve as an entry point for unauthorized access, any automatic software-update mechanism may become an attack vector for remote code execution.

Advances in cryptoanalysis, implementation attacks and computing power threaten any cryptographic algorithm, including PQC algorithms. Thus, crypto agility – the ability to change cryptographic algorithms, keys, and configurations using fast, controlled transitions with minimal disruption – becomes a strategic capability.

Crypto agility reduces long-term risk by enabling faster, safer transitions as standards, threats, and vendor support mature. Crypto agility ensures that security remains intact even when cryptographic algorithms fail.

Q‑Day refers to the point in time when cryptographically relevant quantum computers (CRQCs) become powerful enough to break widely used public‑key cryptography in practical conditions.

The advent of Q-Day is influenced by the pace of hardware advances, in particular circuit depth (number of logical gate operations a system can perform before failure) and operational throughput (logical operations per second), qubit stability (available logical qubits, error correction and connectivity), as well as algorithmic efficiency.

Interested to learn more about quantum computing? Find more information on this page.

Recent breakthroughs from Google Quantum AI in May 2025 and March 2026 (joint work with University of California, Berkeley, Stanford University and Ethereum), Iceberg Quantum in February 2026, and Oratomic in March 2026 (joint work with University of California, Berkeley and California Institute of Technology) drastically reduced the hardware requirements needed to break asymmetric cryptography. 

What required 20 million physical qubits just a bit over a year ago, now requires fewer than one million for RSA, and less than 500,000 for the elliptic curve cryptography.

Furthermore, under newer quantum computer architectures, it might even require fewer than 100,000 physical qubits to break RSA and as few as 10’000 for elliptic curve cryptography.

Notably, these breakthroughs, alongside the roadmaps of IBM, IQM, IonQ and others to build large-scale quantum computers, triggered companies such as Google and Cloudflare to accelerate their post-quantum cryptography migration timelines, setting the deadline for the deprecation of quantum-vulnerable asymmetric algorithms to 2029.