By definition, cryptocurrencies have a lot to do with the ancient art of cryptography, which has been playing a major role in human communication for thousands of years, with the first encrypted messages discovered by archeologists on ancient Egyptian sites. The strategic use of cryptography can be traced back all the way to the Roman times, with Julius Caesar using Caesar Cipher to send secret messages to his high-ranking generals.

The encryption method was very simple: the cipher substituted all the letters in a message by shifting up or down the alphabet, so that the word Aximetria encrypted with a rule of +2 will become Czkogvtkc. Obviously, the complexity of ciphers has evolved since then. During the World War II, the Germans used a machine called the Enigma Machine to encrypt their messages. The code was eventually cracked by a mathematical genius Alan Turing, which is now seen as one of the major turning points in the war.

The Enigma Machine’s cipher was undoubtedly very difficult to crack back then, but in the present day it would’ve been solved in no time at all thanks to the advancement of computer technologies. Most codes can be solved through trial and error, for instance in the Caesar Cipher every letter could only take on 25 different values. Modern day computers can go through millions of possibilities within seconds — cracking a code this was is known as brute force.

With the emergence of cryptocurrencies, there was a need to protect the participants’ privacy and data as well as make mining new tokens inherently difficult. This is where hashing came into play. It’s a method of transforming large amount of data into relatively short strings of numbers and letters that are difficult to imitate. Hashing is used to verify the account balances, encode addresses and transactions. Moreover, miners use the computational resources at their disposal to compete with each other at solving hash functions. Whoever solves it first seals a block and gets a reward.

Another important part of blockchain cryptography are digital signatures — mathematical functions of specific wallets. Digital signatures of both the sender’s and the receiver’s wallets are attached to every transaction and serve as a wallet identification method. With most mineable cryptocurrencies, the difficulty of solving those puzzles is adjusted in correspondence with the amount of miners and the computational power at their disposal. So far, this approach has been working, but there’s a looming threat of of supercomputers and quantum computers and their unmatched computing power. Those will soon be able to crack the currently existing cryptographic cyphers by sheer brute force within mere seconds.

Post-quantum Cryptography

The era of quantum computing is approaching, and as of right now the absolute majority of cryptographic algorithms will not be able to withstand against a hypothetical quantum computer. Even though most currently existing quantum computers that are publicly known lack the processing power to break real cryptographic algorithms, many cryptographers around the world are working on new algorithms to prepare for when quantum computers will finally emerge as a real threat.

Aleksey Fedorov, a scientist from the Russian Quantum Center, has cited the exchange of cryptographic keys between the two parties as the central problem of modern cryptography as a whole. There’s an inherent need for a ‘courier’ that will safely distribute the cryptographic keys. In most blockchains these days, it is the digital signature that plays the role of a courier. It is based on the RSA algorithm, which can be vulnerable to a quantum computer attack, which would jeopardise the entire system.

According to Aleksey, using photons — light particles — as ‘couriers’ might just be the solution here. This is due to the laws of quantum physics: any attempt of interfering with the photon transfer process can easily be detected. Moreover, implementing algorithms that are based on puzzles that are too difficult for a quantum computer to solve into already existing blockchains will make all the immutability of their data invulnerable to the technological process.

Thus, all the weak elements of blockchain architecture can be replaced with means of post-quantum cryptography, further securing the distributed ledger technology. All of this isn’t theoretical — the Russian Quantum Center has already built a quantum-resistant blockchain that is fully operational within the global network and is used by a major Russian bank. All the participants of that ledger identify each other with the help of quantum communications, while the entire system is build in a way that facilitates communication and transactions without the need to trust the person you’re dealing with.