Ethereum’s planned move toward quantum-resistant cryptography could force banks and other regulated custodians to begin preparing by 2027 if they want enough time to adapt before a possible 2029 Layer 1 transition. Thomas Brunner, Sygnum’s head of custody and staking, said the challenge is less about an immediate quantum threat than about how institutional custody systems, recovery processes and compliance frameworks are built. He said future quantum-resistant signature schemes would require strict controls, including not reusing the same key, which can conflict with common bank practices such as duplicating systems, restoring earlier states during backup and disaster recovery, and maintaining failover capabilities. Brunner said identifying a bank’s cryptographic keys and connected systems can take six months to one year before hardware support, certification, internal reviews, external audits and regulatory approvals are completed. He said banks should start with a full inventory of keys and dependent systems, including custody platforms, internal databases, communication channels and third-party services, while also assessing whether hardware security modules and other devices need upgrades or replacement. Sygnum, a digital asset bank headquartered in Switzerland, said the operational burden means institutions that wait too long risk disruption if Ethereum proceeds with a quantum-resistant upgrade timeline that developers are still evaluating.