By 2025, up to 10% of global gross domestic product is likely to be stored on blockchains1. A blockchain is a digital tool that uses cryptography techniques to protect information from unauthorized changes. It lies at the root of the Bitcoin cryptocurrency2. Blockchain-related products are used everywhere from finance and manufacturing to health care, in a market worth more than US$150 billion.
When information is money, data security, transparency and accountability are crucial. A blockchain is a secure digital record, or ledger. It is maintained collectively by users around the globe, rather than by one central administration. Decisions such as whether to add an entry (or block) to the ledger are based on consensus — so personal trust doesn’t come into it. Any party inside or outside the network can check the integrity of the ledger by making a simple calculation.
But within a decade, quantum computers will be able to break a blockchain’s cryptographic codes. Here we highlight how quantum technology makes blockchains vulnerable — and how it could render them more secure.
Blockchain security relies on ‘one-way’ mathematical functions. These are straightforward to run on a conventional computer and difficult to calculate in reverse. For example, multiplying two large prime numbers is easy, but finding the prime factors of a given product is hard — it can take a conventional computer many years to solve.
Such functions are used to generate digital signatures that blockchain users cite to authenticate themselves to others. These are easy to check and extremely difficult to forge. One-way functions are also used to validate the history of transactions in the blockchain ledger. The hash, a short sequence of bits, is der.READ MORE