Quantum computing revolutionizes cybersecurity as both a potent defensive shield and an existential offensive threat to India’s digital sovereignty, imperilling Aadhaar, UPI, Digital India, and critical information infrastructure reliant on classical encryption. This analysis scrutinises its double-edged impact on national data-protection architectures, underscoring the urgency of proactive cryptographic migration under the National Quantum Mission amid accelerating quantum capabilities. Through systematic examination of technological vulnerabilities and regulatory imperatives, the inquiry integrates quantum threat modelling with doctrinal scrutiny of Indian legal precedents to forecast systemic risks and mitigation pathways. Central to the evaluation is a hybrid methodology combining algorithmic deconstruction of Shor’s Algorithm—capable of factoring large integers in polynomial time, thereby nullifying RSA and ECC protocols—with doctrinal analysis of landmark authorities, including Justice K.S. Puttaswamy (Retd.) v. Union of India ((2017) 10 SCC 1; Writ Petition (Civil) No. 494 of 2012) , which elevated privacy as a fundamental right under Article 21 and mandated robust safeguards now enforced by the Digital Personal Data Protection Act, 2023 (DPDP Act) with penalties up to ₹250 crore for security lapses, alongside the Task Force Report on Implementation of Quantum Safe Ecosystem in India (DST, February 2026) directing PQC migration for Critical Information Infrastructure by 2029 to neutralise HNDL risks. Supplementary insights derive from IT Act, 2000 frameworks on encryption interception. Findings affirm QKD’s unconditional security for key exchange yet highlight pervasive retroactive decryption exposure, with lattice-based PQC demonstrating superior resistance under Grover’s speed-up constraints. Implications necessitate immediate cryptographic agility frameworks, elevated corporate liability under DPDP for quantum unpreparedness, and harmonised national standards to safeguard data sovereignty, avert catastrophic breaches in India’s digital economy, and harness quantum-enhanced defences for resilient infrastructures.