In espionage, time has traditionally worked against stolen intelligence. Military plans expire, diplomatic positions change, and the value of a confidential conversation diminishes as events overtake it. An intercepted message that cannot be deciphered today might be worthless by the time someone finds a way to read it.
Quantum computing threatens to disturb that calculation. Some information may remain politically or strategically valuable long after the mathematics protecting it has become obsolete.
There is something peculiar about this possibility. The attack could take place in 2026, the decryption in 2040, and the consequences reach back to decisions made decades earlier. A confidential diplomatic exchange could reveal how a negotiation unfolded. Intelligence records could expose sources whose identities were never meant to become public.
We normally imagine cybersecurity as the protection of the present against intrusion. Here, the object of attack is the past.
India has begun preparing for this possibility, but the implications extend beyond its current discussion of quantum technology. The question is whether our understanding of confidentiality accounts for the fact that information can outlive the security assumptions under which it was created.
In 1994, mathematician Peter Shor demonstrated that a sufficiently capable quantum computer could solve certain mathematical problems efficiently enough to undermine widely used public-key cryptographic systems. The mathematics was established long before engineers possessed the hardware needed to exploit it.
That distinction remains important. Today’s quantum computers cannot practically break modern RSA encryption at scale. Building a fault-tolerant machine with enough reliable computational capacity remains an immense engineering challenge. Quantum computers would not automatically defeat every cryptographic method, either. Yet an intelligence service need not know when such a machine will arrive to consider collecting encrypted material now. The practice is known as harvest now, decrypt later: acquire communications protected by vulnerable cryptography, preserve them, and wait for the computational means to recover their contents.
The economics differ from those of an ordinary cyberattack. A conventional attacker may need to turn stolen information into money or operational advantage quickly. An intelligence organisation can afford a longer horizon. Storage is relatively inexpensive, while the value of certain secrets can persist for decades.
An intercepted payment instruction may become useless once a transaction is completed. The identity of an intelligence source, the details of a weapons system or the deliberations behind a diplomatic settlement could remain consequential far longer.
That difference ought to govern India’s priorities. The US National Institute of Standards and Technology has finalised three principal post-quantum cryptography standards. The challenge is implementing them across systems that depend on older methods, from digital certificates and authentication to secure communications and embedded equipment.
India’s Department of Science and Technology published a quantum-safe migration roadmap in May 2026. It proposes accelerated milestones for critical information infrastructure, including foundational preparation by 2027, high-priority migration by 2028 and full adoption by 2029. Other enterprises have a longer timetable extending to 2033.
This is a serious policy response. What interests me, however, is the assumption that accompanies any timetable: that there is still time to complete the transition.
There may well be. Nobody can reliably date the arrival of a cryptographically relevant quantum computer. But for information already intercepted, the relevant deadline has passed. Replacing an encryption system in 2029 cannot retrospectively protect a message captured in 2026.
This is the central asymmetry. Defenders must upgrade millions of legitimate systems. An adversary needs only to preserve material obtained from a subset of them.
A useful way to frame the risk is to let (X) represent how long information must remain confidential, (Y) the time needed to migrate the systems protecting it, and (Z) the estimated time before a sufficiently capable quantum computer becomes available. If (X+Y) exceeds (Z), the organisation faces a problem even though the machine does not yet exist. This is not a forecast; nobody knows (Z) with confidence. Its value is in exposing a flaw in conventional risk assessment. The arrival of a dangerous capability is not necessarily the moment exposure begins.
India should therefore allocate cybersecurity resources according to the political, economic and strategic lifespan of the information being protected.
A defence communication whose contents become irrelevant within months poses a different problem from intelligence records containing identities that must remain protected for decades. Historical diplomatic archives, industrial research and sensitive personal information raise different questions again. Classification by present sensitivity alone is inadequate; the duration of that sensitivity matters.
There is also an institutional problem. Governments change, officials retire, software vendors disappear and security systems are replaced. The information remains. A future administration may inherit the consequences of a vulnerability introduced long before it took office.
This is why the quantum transition cannot be left entirely to information-technology departments. Cryptographers can evaluate algorithms, but they cannot alone determine how long a diplomatic secret remains dangerous. That requires institutions to assess the information itself, not merely the technology protecting it.
India should require sensitive organisations to connect cryptographic inventories with the expected confidentiality lifetimes of their records. Procurement contracts should account for future migration, and systems that cannot be upgraded without extensive reconstruction deserve particular attention. Institutions must also distinguish between protecting future communications and managing information that may already have been exposed.
None of this diminishes the importance of India’s Rs 6,003.65-crore National Quantum Mission. Developing quantum computing and communication capabilities is a legitimate scientific ambition. But a country does not need to possess a powerful quantum computer to defend itself against one. Post-quantum cryptography can run on conventional machines, although implementing it across large institutions requires substantial engineering.
The harder problem is deciding what deserves protection first.
There is a temptation to frame quantum computing as another technological race. Yet the first country capable of breaking widely deployed public-key cryptography could potentially gain access to an archive of encrypted information collected long before its breakthrough.
Such a capability would not rewrite historical events. It could change who knows what happened, who was involved and which decisions were concealed. In intelligence and diplomacy, that knowledge can have consequences long after the original events.
We cannot establish how much encrypted material has been collected for this purpose, or predict which archives might eventually become readable. Those uncertainties should restrain extravagant claims about an approaching quantum catastrophe, not encourage complacency.
India’s quantum-security challenge is therefore not simply to prepare its computers for the future. It is to recognise that some of the secrets on which its future depends have already entered the past.
The author is a physicist at the University of North Carolina at Chapel Hill and contributor opinion writer at the Wall Street Journal; Views presented are personal.