It’s been almost a year since you left the briefcase of your old documents down in the attic, and today seems like a good day to get it and go through your old files. Although it is the weekend and you would rather just lay back and do nothing, you’ve decided to go get it and be done with it.
Here you are, in front of the briefcase with a blank look on your face. You simply cannot remember the number combination to open it. You thought it is 000 but that didn’t work. There is a faint memory that you may have changed it to… You can’t remember. What do you do now.
In order to open this briefcase without destroying it you need to try up to 1,000 combination from 000 to 999. Hopefully you will get lucky and the briefcase will open early otherwise it might take some time.
This technique is called brute-force attack by hackers.
Lets assume that you can duplicate yourself and the briefcase, stand next to yourself, the “first you” can start from 000 up to 499 and the “second you” can start at the same time from 500 up to 999. Once one of the briefcases is open then you terminate the duplication process and you and the briefcase will merge back to one and go on with your life. You have saved 1/2 of the required time to open this briefcase. The process of being next to yourself seems like a surreal place only seen in paintings or movies. The truth is that this place does exist in the world of quantum mechanics where a particle can be in multiple positions at the same time. Quantum computers are based on quantum mechanics and due to the weird nature of the quantum world a single quantum computer could operate as multiple computers and could solve your briefcase issue extremely fast even if the number of combinations is extremely large.
Every transaction on the blockchain is hashed (has a lock) and contains the hash (lock) of the previous transaction. A collection of transactions are embedded into a block, the block is hashed (has a lock) and contains the hash (the lock) of the previous block, hence, the term blockchain. In order for a hacker to change any transaction on the blockchain, the hacker will have to break all the locks and re-issue new locks to all subsequent transactions and blocks. This has to be done within a fairly short period of time on the majority of the servers which contain the same blockchain in order for the change to be accepted. Using brute-force attack with existing computers seems very difficult. However once quantum computers are ready and functional the task would become much easier.
Bare in mind that a quantum attack on a blockchain is far more difficult than a quantum attack on regular systems. Therefore, regular systems are at risk as well. We can tell that companies using standard systems are getting ready against such attack by implementing a 2 factor authentication which is now enforced by many such as apple, IBM, google… etc.
Another reason for the 2 factor authentication is the release of ASIC based computers to break the lock designed for BitCoin mining. The mining frequency now on BitCoin have reached a high frequency of 20TH/s per machine. This was unheard of a year ago. The blockchain technology is becoming a motive for technological break through.
How can a next generation blockchain be protected from quantum computers. The solution is to use quantum physics. There has been many researches and studies on how to secure a blockchain by using particles and the same properties of quantum laws such as quantum entanglement.