India’s Quantum Leap: From Ancient Philosophy to Post-Quantum Cryptography
A recent explainer traced the conceptual arc of quantum computing, from long-standing philosophical ideas about indeterminacy and duality to the present-day emergence of post-quantum cryptography as a practical policy concern.
It laid out how quantum computers differ fundamentally from classical computers by using qubits rather than binary bits, and why this difference threatens some of today's most widely used encryption methods.
The explainer connected this global technological shift to India's institutional response — chiefly the National Quantum Mission — and to international standard-setting efforts already underway to prepare for a "quantum-safe" future.
It highlighted that while large-scale, fault-tolerant quantum computers capable of breaking current encryption do not yet exist, preparatory transition work is already considered urgent due to the risk of encrypted data being harvested today for future decryption.
Understanding Qubits: Superposition and Entanglement in Quantum Computing
A classical bit stores information as strictly 0 or 1. A qubit (quantum bit), by contrast, can exist in a superposition — a combination of both 0 and 1 states simultaneously — until measured, and multiple qubits can be entangled so that measuring one instantaneously reveals information about the states of the others in ways that have no classical analogue. These properties allow a quantum computer to represent and process an exponentially larger space of possible states in parallel compared with a classical computer using the same number of bits, which is the theoretical basis for quantum computers vastly outperforming classical machines on certain specific problem classes (though not all computational tasks).
Key Details
- Superposition lets a system of n qubits represent up to 2^n combinations of states simultaneously, versus a single fixed value for n classical bits.
- Entanglement is also the basis for quantum cryptography and quantum key distribution, which are being explored as "quantum-safe" secure-communication technologies in parallel with post-quantum classical cryptography.
- "Quantum supremacy" (a term coined in 2012) refers to a quantum computer solving a problem intractable for classical computers; the more commonly used current term, "quantum advantage," refers to a quantum computer completing a task faster or more efficiently than the best available classical supercomputer.
The explainer's framing of "ancient philosophy to post-quantum cryptography" rests on this basic technical distinction — qubits' superposition and entanglement properties are what eventually make certain classical cryptographic problems (like factoring large numbers) solvable in practical time by a sufficiently powerful quantum computer, which is not possible for classical computers.
Shor's Algorithm and the Threat to RSA/ECC Encryption
Shor's algorithm is a quantum algorithm that can efficiently factor large integers and solve the discrete logarithm problem — the two mathematical problems that underpin the security of RSA encryption and Elliptic Curve Cryptography (ECC), both widely used today to secure banking transactions, government communications, and internet traffic. On a classical computer, factoring a sufficiently large number underlying an RSA key would take longer than the age of the universe; on a large enough fault-tolerant quantum computer, Shor's algorithm could in principle perform this in a practical timeframe, rendering current public-key encryption schemes insecure once such hardware exists.
Key Details
- Public-key systems threatened include RSA (based on integer factorisation) and ECC/Diffie-Hellman (based on the elliptic-curve discrete logarithm problem) — both foundational to internet security protocols such as TLS/HTTPS.
- Large-scale fault-tolerant quantum computers with the thousands of stable logical qubits needed to run Shor's algorithm at cryptographically relevant scale do not yet exist, but the "harvest now, decrypt later" risk — adversaries storing encrypted data today to decrypt once capable quantum computers arrive — is already treated as a present-day threat by cybersecurity and government agencies.
- This risk is the core rationale for developing post-quantum cryptography (PQC): new encryption algorithms designed to be secure against both classical and quantum attacks, without needing a quantum computer to run them.
The explainer's discussion of "post-quantum cryptography" is a direct response to the Shor's-algorithm threat model — the urgency of migrating to quantum-resistant algorithms stems from the "harvest now, decrypt later" risk, not from quantum computers being an immediate practical reality.
NIST Post-Quantum Cryptography Standards
The U.S. National Institute of Standards and Technology (NIST) finalised its first three post-quantum cryptography standards on August 13, 2024, after an eight-year, multi-round international evaluation process: ML-KEM (FIPS 203, derived from CRYSTALS-Kyber, for key encapsulation/key exchange), ML-DSA (FIPS 204, derived from CRYSTALS-Dilithium, for digital signatures), and SLH-DSA (FIPS 205, derived from SPHINCS+, a hash-based signature scheme). These lattice-based and hash-based algorithms are designed to resist attacks from both classical and quantum computers, and organisations worldwide, including in India, are being encouraged to begin migration planning.
Key Details
- ML-KEM and ML-DSA rely on the mathematical hardness of lattice problems (Module-Learning-With-Errors and Module-Short-Integer-Solution), believed to remain hard even for quantum computers, unlike factoring/discrete-log problems broken by Shor's algorithm.
- SLH-DSA's security rests solely on the properties of cryptographic hash functions, offering a structurally different (hash-based) fallback signature scheme.
- NIST advanced additional post-quantum signature candidates in a second evaluation round after the 2024 standards, indicating this is an ongoing, multi-year standardisation effort rather than a one-time event.
The explainer's reference to India "navigating the paradigm shift" maps onto this global NIST-led standardisation process — Indian government and financial-sector systems, like those elsewhere, will eventually need to migrate to NIST-standardised (or India-specific) post-quantum algorithms to remain secure once quantum computers mature.
India's National Quantum Mission (2023)
The National Quantum Mission (NQM) was approved by the Union Cabinet on April 19, 2023, with a total outlay of Rs 6,003.65 crore for the period 2023-24 to 2030-31, aimed at seeding, nurturing, and scaling up scientific and industrial R&D in quantum technology to build a vibrant innovation ecosystem. The Mission established four Thematic Hubs (T-Hubs) at leading institutions to lead research across the Mission's core focus areas.
Key Details
- Quantum Computing Hub: Indian Institute of Science (IISc), Bengaluru.
- Quantum Communication Hub: IIT Madras and the Centre for Development of Telematics (C-DOT), New Delhi.
- Quantum Sensing and Metrology Hub: IIT Bombay.
- Quantum Materials and Devices Hub: IIT Delhi.
- The Mission has engaged researchers from dozens of institutions across multiple states, working through thematic groups covering the Mission's priority research areas, and has approved numerous academic institutions to set up quantum teaching laboratories.
The National Quantum Mission is India's institutional vehicle for building indigenous capability across both quantum computing and quantum-safe communication research — directly relevant to the explainer's framing of India "navigating" the global quantum and post-quantum cryptography transition, since the Mission's Quantum Communication Hub specifically addresses secure-communication technology relevant to the PQC transition.
- National Quantum Mission: approved by the Union Cabinet on April 19, 2023; total outlay Rs 6,003.65 crore for 2023-24 to 2030-31.
- Four Thematic Hubs: Quantum Computing (IISc Bengaluru), Quantum Communication (IIT Madras and C-DOT New Delhi), Quantum Sensing and Metrology (IIT Bombay), Quantum Materials and Devices (IIT Delhi).
- NIST finalised its first post-quantum cryptography standards on August 13, 2024: ML-KEM (FIPS 203), ML-DSA (FIPS 204), SLH-DSA (FIPS 205).
- Shor's algorithm threatens RSA (integer factorisation) and ECC/Diffie-Hellman (elliptic-curve discrete logarithm) — the mathematical bases of most current public-key encryption.
- "Quantum supremacy" term coined in 2012; commonly superseded today by "quantum advantage" terminology.
- A qubit's superposition allows n qubits to represent up to 2^n simultaneous state combinations, versus one fixed value for n classical bits.