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Quantum computers threaten data encryption

When we encrypt our data using private and public keys, we consider it safe, and we are assured. However, reality is that our current encryption technology is just that, a technology, and new breakthroughs in technology tend to make earlier technologies obsolescent. Quantum computing, a technology yet to be commercialized, is threatening to make out private keys and public keys potentially irrelevant.

New threat to data encryption from quantum computers

When we encrypt data, essentially the cryptographic algorithm converts plain text into scrambled ‘ciphertext’, and it uses a unique key for this process. A complementary algorithm can convert this ciphertext into plain text again, and this is decryption. This complementary algorithm will again use that unique key. Without that key, decryption isn’t possible. When we use public and private key-based encryption, the public key can be shared with someone else, whereas the private key must remain with the user as confidential.

If a hacker can access your private key, he can easily create the public key, however, with only the public key, it’s extremely hard to create the private key. This is because the public and private keys are linked to each other by integer factorisation. To refresh our memory from school days, factorisation is about decomposing a number into the factors of it, for e.g. the number 3663 is factorised into 3x3x11x37. The larger the number is, the harder it is to arrive at the factors. The computers we use today will take extremely long time to factorise very large numbers. This is what makes creating the private key from the public key so very hard, in fact nearly impossible, for today’s computers.

But then today’s computers are classical computers, which represent information as “binary digits”, or “bits”, i.e. sequence of zeroes and ones. Each bit can only hold “0” or “1”, there is no other possibility. The technology that’ll change this is quantum computing, where quantum bits, or “qubits” are used instead of bits. Qubits can hold a superposition of “0” and “1” states at any time. The more the qubits, the larger is the number of states simultaneously held by the collection of qubits.

When quantum computers process qubits, they actually use algorithms using something known as quantum gates, which are essentially building blocks operating simultaneously on all possible states of all the qubits. Quantum computers can potentially operate much faster than our classical computers. This is what threatens the integer factorisation-based encryption technology, because a quantum computer can resolve the puzzle of factorising a very large number very quickly.

What is symmetrical encryption algorithm?

In addition to integer factorisation based encryption technology, we also have symmetrical encryption, where there is only one encryption key. A symmetrical encryption algorithm, for e.g. AES, works very well, because of the sheer volume of work a hacker’s computer needs to do to hack this key. A 56-bit encryption actually means that the hacker’s computer needs to search 256 keys, i.e. a mind-boggling 72,057,594,037,927,936 keys, to find the correct encryption key! While faster factorisation capability of a quantum computer will not help here, another algorithm of quantum computing, called “Grover’s Algorithm” can reduce the volume of search to 228, or 268,435, 456, which is eminently more manageable! There is, however, a good news in case of symmetrical encryption technology, because the key length can be increased. Experts suggest a 256-bit key length to adequately address threat posed by quantum technology, i.e. 2256 searches.

If you are a cryptocurrency miner, after reading the above you might be thinking that while the current encryption technologies are threatened by the quantum computers, your mining process is actually quite safe, because of the underlying blockchain that powers your Bitcoin or Ether. Not forever, as we shall see. Blockchain is a distributed database, where every node is equal point of authority, and can update blockchain if the transaction is approved by the consensus mechanism of blockchain. In the decentralized network that blockchain is, maintaining the order of transactions is crucially important, to maintain data integrity.

Updating blockchain is essentially creating a new block, and that’s what miners do by providing proof of work (POW), in the form of the transaction record of the block he is trying to create, as well as the reference to the last recorded block in the blockchain. Providing POW in this manner, i.e. identifying the reference to the last recorded block, is actually a massive number-crunching operation. It boils down to repeatedly trying one number after another very fast, until the reference to the last recorded block is found. This is done in an intensely competitive environment, since cryptocurrency miners are rewarded with a fraction of the tokens they mine. This requires heavy-duty computing power. If a user, or a group of users, can control over 50% of the computing power of the network, then they can force the system to discard valid transactions even before they are recorded in the blockchain, and thereby hack the decentralized network. Now, imagine a node powered by an immensely powerful quantum computer and controlled by someone with malicious intent, and a hacking of blockchain network seems possible.

At least for the time being, there is good news for the cryptocurrency miners. A group of students in the National University of Singapore, led by Divesh Aggarwal, has concluded after researching the developments in the quantum computing space, that at least for the next 10 years, conventional cryptocurrency mining computers will maintain a lead over the quantum computers in terms of processing power.

Nevertheless, the threat to encryption technology from quantum computing is real, and institutions and communities are waking up to it. America’s NIST (National Institute for Standards and Technology) is evaluating proposals for encryption technologies that will be resistant to quantum computing. Cryptocurrency developers have started to take this seriously too, and Quantum Resistant Ledger (QRL) was developed keeping this threat in view. The Russian Quantum Centre is researching with the objective of developing blockchain solutions that will be resistant to quantum computing.