Why is Quantum Computing a threat to Modern Day Cryptography?
Quantum Mechanics is the basis on which Quantum Computers are being built upon and will radically impact the way modern day Cryptography works,in the future.
Regular computers store information using transistors,which work like tiny switches,where a flow of current represents a 1 and an absence of current is used to represent a 0. Each 1 or 0 is stored as a ‘Bit’. Modern day Encryption, for example Asymmetric Encryption works by using a pair of keys; a public key and a private key. The private key isn’t known to anyone,except the owner and the public key can be publicly distributed without compromising any security. The generation of both keys is dependent on “cryptographic algorithms which are based on mathematical problems termed one-way functions.”¹ The public key is used to encrypt a plaintext message and the private key is used by the receiver to decrypt this message.² However,Quantum Computers use a different method for data storage and encryption.
To understand Quantum Computing, we need to first explore the fundamentals of Quantum Mechanics. At the end of the 18th century,the English polymath Thomas Young,³ conducted his famous Double Slit experiment;this experiment involved shining light at a partition,where there were two narrow vertical slits. The light was observed as diffracting and forming an interference pattern on a screen,some distance beyond the slits.The formed pattern on the screen was of several light and dark stripes.
However, modern technology allows physicists to reproduce Young’s experiment with only a single photon of light being emitted by a filament bulb. Using specialised equipment⁴, the pattern displayed on the screen during the Young’s Double Slit experiment,was the same pattern observed when only a single photon was fired at the slits. This unexpected result is still being debated by Quantum Theorists but there are two main explanations,so far.
The first idea uses the principle of superposition. There are two main facts that we are aware of: the photon left the filament bulb and that it strikes the screen. What we don’t know, is whether the photon entered the left slit,or the right slit. Due to the ambiguity of the photon’s motion,Superpositionists³ take on the view that the photon somehow passed through the slits simultaneously. They argue that, because we don’t know what the particle was doing,then it’s allowed to do everything possible,simultaneously. Each possibility is known as a ‘state’ ,“and because the photon fulfils both possibilities it is said to be in a superposition of states .”³ This idea can be elaborated by using the Schrödinger’s cat,parable.
The second interpretation of Young’s modified experiment is the many-worlds interpretation. The theory,simply put, is that “there are many worlds which exist in parallel at the same space and time as our own. The existence of the other worlds makes it possible to remove randomness and action at a distance from quantum theory and thus from all physics.”⁶ When the photon exits the filament bulb,it has two choices ,it can either enter the left slit or the right slit. The theory suggests that when the photon undergoes either of these possibilities, the universe divides into two universes. In one universe, the photon enters the left slit and in the other, the universe enters the right slit. Both universes interfere with each other,which causes the striped pattern to be displayed on the screen.
Quantum Computers use these fundamentals of Quantum Mechanics to solve problems. For example,if we were to solve questions on a modern computer, you would input the first question,wait for an output and then input another question and wait for that output. In other words, the processing is done sequentially. Whereas, on a Quantum Computer the questions would either be combined as a superposition of two states and inputted simultaneously or, using the many-worlds interpretation, the machine would enter two different universes and the questions answered according to each universe. In any case, the questions will be answered a lot faster than a contemporary computer.
As mentioned beforehand, modern systems represent data as binary digits, either a 1 or a 0. In Quantum Computers , data can be represented using fundamental particles. Many fundamental particles have an inherent spin, they either spin eastwards or westwards. This spinning motion can be used to represent either a 1 or a 0; a spin eastwards represents a 1 and a spin westwards represents a 0. When inputting data into the computer, the particles will either superpose to represent both 1s and 0s or they can be thought of as entering the two universes ,in which one has a particle spinning westwards, and one universe has a particle spinning eastwards. Due to this quantum superposition, each spinning particle can be represented using quantum bits-Qubits! The advantage of Qubits is that it is capable of carrying out a huge number of computations,which can thus be used to crack current encryption algorithms, in a matter of seconds. For example, with 250 qubits, “it is possible to represent roughly 10⁷⁵ combinations,which is greater than the number of atoms in the universe.”³ This would mean that a Quantum Computer would be able to carry out that many computations ,in just one second.
In 1996,Lov Grover discovered a program to search through lists at incredibly high speeds.³ Astonishingly,this program is exactly what’s required to crack a Data Encryption Standard (DES) cipher. A DES cipher involves searching through a list of keys,to find a match. A conventional computer is able to check through 10 ⁶ combinations of hexadecimal digits per second,which would mean it would take over 10 ³ years to crack this cipher. In comparison, when using Grover’s program,the key would be able to be found in less than 4 minutes. Ciphers like the RSA (Rivest–Shamir–Adleman), AES(Advanced Encryption Standard) and DES,which are used to encrypt our emails,data,financial transactions could all be cracked in very small timescales,if the power of Quantum Computers can be harnessed correctly. If successful Quantum Computers are built, then national security, individual privacy and digital commerce will all be jeopardised. Whichever country manages to build a truly functional Quantum Computer , will have the power to crack any encryption algorithm and gain access to any information they require, at their fingertips.
Written by: Muskan Sharma
Bibliography
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