The transition to post-quantum cryptography presents significant challenges, particularly in systems where individual users manage their own cryptographic keys, such as blockchains. Experts note that the increased key and signature sizes required by new algorithms can break assumptions in older protocols and systems, while the decentralized nature of user-held keys complicates large-scale migrations.
When organizations undertake a comprehensive inventory of their cryptographic assets, common discoveries include default passwords that were never changed, hidden administrative keys still accessible by former employees, and password hashes stored on user devices. In one instance, a password hash was extracted from a laptop's cache to access a password manager.
The larger key and signature sizes of post-quantum algorithms can exceed limitations in systems designed decades ago. Protocols like IPsec, SSH, and TLS, as well as the widely used peer-to-peer networking library libp2p, have been found to contain implicit assumptions about message sizes that are violated by the new primitives, sometimes resulting in unhelpful error messages. Updating libp2p, for example, required adjustments to accommodate these larger sizes.
Achieving cryptographic agility, which involves abstracting cryptographic functions to allow for easy algorithm changes, is a complex endeavor. While AI-assisted coding can reduce the technical hurdle, implementing this abstraction across numerous systems and organizational boundaries adds friction. Blockchains are particularly difficult to upgrade due to the need for every user to actively migrate their keys, even when account abstraction simplifies the technical aspects.
The potential for a "silent quantum break," where a sophisticated adversary could remotely compromise cryptographic keys without detection, is a concern. Such an attack would likely be evident only through the absence of other explanations for widespread key compromises, making it difficult to definitively attribute to a quantum breakthrough. A recent hardware wallet compromise, for instance, was eventually traced to a weak random number generator, but without that forensic discovery, a mathematical break might have been suspected. If a quantum attacker were to simultaneously compromise many keys across diverse systems and vendors, it could raise suspicions of a mathematical breakthrough, though certainty would remain elusive until a public demonstration or advanced mathematical proofs emerge.
Funding for post-quantum migration, which offers an invisible payoff if successful, is often framed as a risk management exercise, akin to purchasing insurance. Quantifying the potential financial losses from a cryptographic failure versus the cost of migration can persuade capital allocators. Some venture firms have re-evaluated their portfolios after realizing the extensive time and effort required for user key migration in blockchain systems, highlighting that waiting for others to suffer quantum-related losses would be too late.
