Blockchains are secure and trusted at this moment in time, but as we march towards the era of quantum computing there are deep threats to the fundamentals currently in use.
Since there are copies of the ledger stored on each full node in a blockchain network, these records will be around for a long time. This is an important issue for currencies that have zero-knowledge anonymous transactions.
Important distinction: I mean that one transaction can’t be tied to the sending or receiving addresses that took part in the exchange of funds. I am not referring to the concept of anonymity that has been claimed where private keys/ accounts aren’t tied to names.
As we approach the limits of silicon transistor density, quantum computing could be a target for the massive R&D funding that is currently poured annually into wafers and dies. Quantum computers are very good at certain tasks such as factoring primes. The problem is that much of our current cryptography relies on classical computers being very slow at achieving this specific task. There are variants of algorithms that can target specific asymmetric key cryptosystems that are the basis of many blockchains. The news isn’t all bad though, first of all we likely have a lot of time before this becomes any kind of issue, and there are many proposals for methods to “quantum-harden” cryptographic systems specifically in blockchain.
Nathana Sharma provides a great overview of the subject in Is Quantum Computing an Existential Threat to Blockchain Technology?
I’ll be diving deeper into a couple of specific facets of blockchain’s future soon, so stay tuned.
Brandon Rodenburg, PhD Stephen P. Pappas, PhD .Blockchain and Quantum Computing. June 2017. MITRE Technical Report. Project No.: 25SPI050-12