Bridging the Divide: Structural Vulnerabilities in Blockchain Interoperability and the Emerging Threat of Quantum-Enabled Cryptographic Compromise: A Systematic Literature Review

Cross-chain bridges connect blockchains that cannot talk to each other natively, and they have become one of the mostfrequently attacked parts of the ecosystem. The six largest bridge incidents of 2021–2022 alone account for roughly $2.4billion in reported losses. Most of these losses trace back to three things: stolen signer keys, flawed signature checks, andweak message authentication. Almost every bridge also relies on elliptic-curve signatures (ECDSA on secp256k1), which alarge fault-tolerant quantum computer running Shor’s algorithm could break. The bridge literature and the post-quantumliterature have mostly been written separately. We argue that the two problems compound each other, and we call thiscompounded exposure dual fragility. Using a PRISMA 2020 systematic review of 87 papers and technical documents, we(i) map bridge architectures by trust model and quantum exposure, (ii) classify the main exploit patterns, (iii) compareNIST post-quantum signature schemes by size overhead under bridge conditions, and (iv) describe a simple game-theoreticmodel showing why independent chains tend to delay migration. We identify five interacting dimensions of dual fragility:architectural fragmentation, trust concentration, cryptographic dependence, governance rigidity and scalability pressure. Ourmain conclusion is that coordination, not cryptography, is the harder part of migration. The cryptographic tools exist; thegovernance processes needed to deploy them across many chains do not yet.