Quantum cryptography bitcoin network
The miners then start work on the next block. Occasionally, two mining groups find different nonces and declare two different blocks. The Bitcoin protocol states that in this case, the block that has been worked on more will be incorporated into the chain and the other discarded.
In that case, it effectively controls the ledger. If it is malicious, it can spend bitcoins twice, by deleting transactions so they are never incorporated into the blockchain. The other 49 percent of miners are none the wiser because they have no oversight of the mining process. That creates an opportunity for a malicious owner of a quantum computer put to work as a Bitcoin miner.
If this computational power breaks the 50 percent threshold, it can do what it likes. Their conclusion will be a relief to Bitcoin miners the world over. Aggarwal and co say that most mining is done by application-specific integrated circuits ASICs made by companies such as Nvidia.
But there is a different threat that is much more worrying. Bitcoin has another cryptographic security feature to ensure that only the owner of a Bitcoin can spend it. This is based on the same mathematics used for public-key encryption schemes. The idea is that the owner generates two numbers—a private key that is secret and a public key that is published.
The public key can be easily generated from the private key, but not vice versa. A signature can be used to verify that the owner holds the private key, without revealing the private key, using a technique known as an elliptic curve signature scheme.
In this way, the receiver can verify that the owner possesses the private key and therefore has the right to spend the Bitcoin. The only way to cheat this system is to calculate the private key using the public key, which is extremely hard with conventional computers. But with a quantum computer, it is easy. Indeed, quantum computers pose a similar risk to all encryption schemes that use a similar technology, which includes many common forms of encryption.
There are public-key schemes that are resistant to attack by quantum computers. So it is conceivable that the Bitcoin protocols could be revised to make the system safer. But there are no plans to do that now. Bitcoin is no stranger to controversy. It has weathered various storms over its security.
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These cows are modeling the tracking technology of the future. The researchers from Singapore, Australia and France say that scenario represents the worst case, and would see a quantum computer able to run Shor's algorithm against the cryptocurrency's protective elliptic curve signature quicker than the 10 minutes Bitcoin needs to record a transaction in the blockchain.
There are two items of good news in the paper for Bitcoin: In their paper , which landed at arXiv in late October, Divesh Aggarwal and his collaborators say ASIC-based mining rigs are fast compared to even optimistic theoretical quantum computer clock speeds.
The extreme speed of current specialized ASIC hardware for performing the hashcash PoW, coupled with much slower projected gate speeds for current quantum architectures, essentially negates this quadratic speedup, at the current difficulty level, giving quantum computers no advantage. Future improvements to quantum technology allowing gate speeds up to GHz could allow quantum computers to solve the PoW about times faster than current technology.
As far as defeating hashcash goes, the numbers are daunting for quantum computer designers: Shor's algorithm, a quantum algorithm for factoring integers that's how it would attack cryptography , is a better path, they write. Deploying a quantum computer against the secpk1 elliptic curve Bitcoin uses is much more dangerous: As with cracking the proof-of-work, the researchers assume quantum computers get big and fast relatively quickly, and even so, they fall slightly short: Minds Mastering Machines - Call for papers now open.
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