Bitcoin is theoretically vulnerable to being cracked by quantum computers, but calculations show they would need to be a million times larger than those that exist today.
Quantum computers would need to become about a million times larger than they are today in order to break the algorithm that secures bitcoin, which would put the cryptocurrency at risk from hackers.
The bitcoin network is kept secure by computers known as miners that use a cryptographic algorithm called SHA-256, which was created by the US National Security Agency. Breaking this code is essentially impossible, for ordinary computers, but quantum computers, which can exploit the properties of quantum physics to speed up some calculations, could theoretically crack it open.
Now Mark Webber at the University of UK, and his colleagues have investigated how large a quantum computer you would need to break bitcoin, in terms of the number of quoits, or quantum bits, the equivalent of ordinary computing bits.
Every bitcoin transaction must be confirmed by the network of miners before it is added to the blockchain, the immutable ledger of who owns what. Each transaction is assigned a cryptographic key during this confirmation process, and cracking the key would allow you to take ownership of those bitcoins.
The transactions get announced and there is a key associated with that transaction, says Webber. And there is a finite window of time that that key is vulnerable and that varies, but it’s usually around 10 minutes to an hour, maybe a day.
Webber team calculated that breaking bitcoin's encryption in a 10-minute window would require a quantum computer with 1.9 billion quoits, while cracking it in an hour would require a machine with 317 million quoits. Even allowing for a whole day, this figure only drops to 13 million quoits.
This is reassuring news for bitcoin owners because current machines have only a tiny fraction of this IBM’s record-breaking superconducting quantum computer has only 127 quoits, so devices would need to become a million times larger to threaten the cryptocurrency, something Webber says is unlikely to happen for a decade.
Although bitcoin is secure for the foreseeable future, there are concerns about other encrypted data with a much wider window of vulnerability. An encrypted email sent today can be harvested, stored and decrypted in the future once a quantum computer is available also called harvest now, decrypt later attack, which some security experts believe is already happening.
People are already worried because you can save encrypted messages right now and decrypt them in the future, says Webber. So there is a big concern we need to urgently change our encryption techniques, because in the future, they are not secure.
Today, there are few people who have not heard about bitcoin. And, yet, just as few people seem to understand how it works. Perhaps that is to be expected. The way in which the bitcoin protocol processes transactions is new and fundamentally different from traditional payment mechanisms. Whereas traditional payment mechanisms employ decentralized or centralized clearing mechanisms, bitcoin transactions are processed via a distributed clearing mechanism.
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