The enduring quantum vulnerabilities of cryptocurrencies

Major cryptocurrencies such as Ethereum and Bitcoin will ultimately need to migrate to post-quantum signature schemes in order to avoid compromise from cryptographically relevant quantum computers. But even if such protocol migrations occur in a timely fashion, both blockchains will exhibit enduring vulnerabilities. For example, hundreds of billions of dollars worth of these assets with exposed public keys are secured by presumably "lost" private keys. Without those private keys, these assets cannot be transacted into a quantum-secure protocol and will remain exposed to eventual quantum attack. Likewise, in the case of Ethereum the loss of private keys will in some cases preclude updating "immutable" smart contracts that have elliptic curve cryptography hard-coded into the ledger. This talk will introduce these issues and briefly discuss interesting technical, economic and political questions that arise in trying to resolve them.