Quantum Cryptography

---

---

Public key cryptography is the method which is mainly used to keep information secure by exchanging the keys. It is slower than other methods, so it is mainly used to share the keys besides encrypting a large amount of data.

For example, systems like RSA and Diffie-Hellman are often used to share keys between different parties. But because they're slower, many places use a mix of public key and shared key systems. This way, they get the speed of shared keys and the security of public keys.

However, there are some risks with public key systems. They rely on the idea that certain math problems are really hard to solve. But if computers get much faster or new math tricks are discovered, these systems might not be safe anymore.

So, there's a chance that future technology or math discoveries could make public key systems less secure. This could be a big problem for things like national security or protecting secrets. If that happens, we will have to spend a lot of time and money finding a new way to keep information safe.

What is Quantum Cryptography?

Quantum cryptography, also known as quantum encryption, is one of several cybersecurity solutions for encrypting and transferring secure information that depend on the naturally occurring and immutable laws of quantum mechanics.

Basics of Quantum Mechanics

Mainly quantum cryptography is based on the basic fundamentals of quantum mechanics −

• At the quantum level, particles can exist in multiple locations or states at the same moment. And it is difficult to forecast their specific quantum state.
• Photons, the smallest particles of light, can be assigned unique polarities, or spins, that can serve as a binary counterpart to the ones and zeros of classical computational systems.
• As per the quantum physics rules, just measuring or viewing a quantum system has a measurable effect on that system.
• While the properties of some particles can be replicated, a complete clone is considered to be impossible.

How Quantum Cryptography work?

Quantum cryptography, also known as quantum key distribution (QKD), sends data across a fibre optic connection using a series of photons. By comparing measurements of the properties of a subset of these photons, the two endpoints can figure out what the key is and if it is secure to use.

Breaking down the process helps to describe it better −

• The transmitter sends photons using a filter that randomly assigns them one of four polarisations and bit designations: Vertical (one bit), horizontal (zero bit), 45 degrees right (one bit), and 45 degrees left (zero bit).
• The photons are sent to a receiver, which uses two beam splitters (horizontal/vertical and diagonal) to "read" the polarisation of each photon. The receiver is unable to figure out which beam splitter to use for each photon and can guess.
• Once the photon stream has been sent, the receiver informs the sender of which beam splitter was used for each photon in the series, and the sender matches that information to the polarizer sequence used to send the key. The photons read with the incorrect beam splitter are eliminated, and the resulting sequence of bits forms the key.

If an eavesdropper reads or copies the photon, its status changes. The modification will be detected by the end points. In other words, you cannot read, forward, or replicate the photon without being noticed.

Example

In this example, Alice and Bob are using Quantum Key Distribution (QKD) to send a secret message securely. Here is how it works −

• Alice wants to send a secret message to Bob, but they need a secure way to do it.
• Alice sends photons (light particles) to Bob over a fibre optic cable. Each photon has a unique feature known as polarisation, which can be horizontal, vertical, diagonal, or antidiagonal.
• Eve, with malicious intent, wants to listen in on Alice and Bob's talk. Eve tries to decipher the secret message by reading the photons as they go through the connection.
• However, when Eve attempts to read a photon, she alters its quantum state. This change introduces errors into the quantum key that Alice and Bob use to encrypt their communications.
• Alice and Bob are intelligent. They have built up their system to detect changes to the quantum key. When they find errors in the key, they know that someone, possibly Eve, was messing up with their connection.
• To be secure, Alice and Bob quickly discard the compromised key. They know it is no longer secure because Eve tampered with it.
• Alice then generates a new key that has not been compromised. She safely sends the new key to Bob.
• Now that they have a secure key, Bob can decrypt Alice's secret message. Because they identified and prevented Eve's eavesdropping effort, they can communicate without fear of their message being intercepted.

Attacks in Quantum Cryptography

Quantum cryptography was developed to be highly secure, but it is not resistant to all threats. Some possible attacks on quantum cryptography are −

• Trojan horse attacks − In this kind of attack, the eavesdropper, can interfere with the quantum devices used for communication. Eavesdropper may have unauthorised access to the secret key being shared by introducing issues or vulnerabilities.
• Side-channel attacks − These attacks take advantage of vulnerabilities in how the quantum cryptography system is set up physically. For example, Eavesdropper can track power usage or electromagnetic signals from devices to find out more information about the secret key.
• Photon number splitting attacks − Eavesdropper captures the photons that Alice sends. He can take information without Alice or Bob knowing because of the mechanism known as photon number splitting. Some protocols for quantum key distribution can be vulnerable to this type of attack.
• Quantum memory attacks − Eavesdropper can use a special device known as a quantum memory in some cases. This lets Eavesdropper to store quantum information without disturbing it. Eavesdropper can return later and measure the stored information to find the secret key without being detected.

Security of Quantum Cryptography

Quantum cryptography is very secure because it follows to the principles of quantum physics, the study of small particles. If someone interferes with the photons sent between Alice and Bob, their state changes. Alice and Bob will detect the disturbance, which indicates the presence of someone attempting to listen in. This is all due to the "no-cloning theorem," which states that you cannot create an exact replica of a quantum state that you do not completely understand. So, basically, quantum communication's security is guaranteed by physical rules, making it impossible to attack.

Applications

Quantum cryptography has the power to change the way we communicate by offering a highly secure mechanism for sending information that is resistant to cyber-attacks. Here are some of the applications −

• Using quantum cryptography, we can ensure that our financial transactions are completely secure. Cybercriminals will be impossible to steal important financial information because it is secured by quantum power.
• Quantum cryptography could be used by military and government personnel to communicate sensitive information without risk of being detected. It is similar to having a super-secure phone line that is hacker-proof.
• It can secure our health information. Whether it can be health information or medical research, our sensitive healthcare data will be secure from cyberattacks.
• Quantum cryptography could make our smart devices, like smart thermostats and door locks, safe to use. These gadgets usually have limited computational capability, making them easy targets for hackers. But with Quantum Cryptography, their communication routes will be extremely safe.

Advantages

Quantum cryptography offers enhanced internet security by using some rules −

• Can detect eavesdropping and allow the receiver to request another key.
• Provides a variety of security mechanisms.
• Because quantum states change rapidly, they are nearly impossible to attack.
• Provides a variety of security options.

Drawbacks

Quantum cryptography's drawbacks are as follows −

• Quantum Cryptography is limited to short distance use.
• Extremely costly to set up on a large scale.
• In real life, the technology is still in its early stages.
• There could be an effect on photon polarisation in the travelling medium.

Classical Cryptography vs. Quantum Cryptography

On the basis of type of encryption and decryption of the message we can distinguish between Classical and Quantum Cryptography as follows −