Quantum computing poses a threat to blockchain technology because it upends the basic security assumption of elliptic curve cryptography, namely, that computers cannot factor large numbers effectively.

In today’s traditional and legacy blockchains, the most common form of public key/private key pairing is one based on the Elliptic Curve Digital Signature Algorithm (ECDSA). ECDSA works on the the security assumption that computers, even very powerful ones, cannot break down very large numbers in human amounts of time and break blockchain keys. Most legacy blockchains rely on ECDSA.

In ECDSA public-key cryptography systems, anyone can send transactions or messages to a public key, but only the holder of the paired private key can access what has been sent to the public key/address. It’s like a mailbox — anyone can stick letters in through the front slot, but one needs the (private) key to open up the back and take anything out of it. The security of a blockchain is guaranteed by its cryptographic functions, and the most common one in the industry is at risk in the face of quantum computing. Additionally, unlike centralized systems, decentralized systems need the active consent and participation of all users to achieve something like total address type migration, which is what would be necessary to achieve quantum resistance.

While quantum computing does pose a threat, it is not the only technology that is at risk. Banks, companies and countries using blockchain will be targeted if it develops to the point where quantum computers can unravel blockchain code.

Public-key cryptography is a common technique used for encryption and authentication. Internet connections (HTTPS), blockchains, and many other applications use this technique. In most cases, their security relies on hard mathematical problems such as integer factorization, which can’t be cracked easily by a traditional computer.

In theory, a sufficiently powerful quantum computer would, however, be able to solve these problems efficiently. If that happens, he said, then the problem is much larger than just bitcoin — people would be able to crack most forms of cryptography used nowadays.