Quantum computers could threaten blockchain security.

Blockchain's vulnerability to quantum computers comes from its extensive reliance on cryptography. 

 

The technology, also called a distributed ledger, is essentially a computational system in which information is securely logged, shared and synchronized among a network of participants. The system is dynamically updated through messages called transactions, and each participant can have a verified copy of the system's current state and of its entire transaction history. 

 

For this type of decentralized data-sharing system to work requires strict security protocols – not only to protect the information and communications in the blockchain, which are often sensitive, but also to confirm the identity of participants, for example thanks to digital signatures. 

 

These protocols, for now, rely on classical cryptography keys, which transform information into an unreadable mush for anyone but the intended recipients. Cryptography keys are used to encrypt data – data that can in turn only be read by someone who owns the right key to decode the message. 

 

The strength of encryption, therefore, depends on how difficult it is for a malicious actor to decode the key; and to make life harder for hackers, security protocols currently rely on algorithms such as RSA or the digital signature algorithm to generate cryptography keys that are as complex as possible. Those keys, in principle, can only be cracked by crunching through huge amounts of numbers.  

 

This is why most current cryptography protocols are too hard to decode – at least with a classical computer. But quantum computers, which are expected to one day possess exponential compute power, could eventually crack all of the security keys that are generated by the most established classical algorithms.

 

By using Shor's algorithm, a quantum attacker is able to calculate the private key of a user on the basis of their signed message, which is impossible to do with classical computers, and in this way, impersonate any party they want

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