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Quantum Cryptography and Encryption: How It Works

Asloob Alam

The quantum era will not support traditional encryption anymore. We need a more secure type of encryption to combat the threat of quantum computers. We are fortunate to have brilliant minds working on the solution worldwide. And quantum cryptography is the answer.

What is Quantum cryptography?

Quantum cryptography is a field that utilizes principles of quantum mechanics to secure communication and protect sensitive information. It extends robust security by leveraging the fundamental properties of quantum physics. Quantum encryption, on the other hand, refers to applying quantum cryptography techniques to encrypt data that eventually faces the challenge of quantum computers.


Quantum cryptography is divided into two groups. The first is a hardware-based concept called Quantum Key Distribution (QKD), which uses basic ideas from quantum mechanics to enable secure communication that is not compromised through eavesdropping. The second method uses Post-Quantum Cryptography (PQC), a software technique. In contrast to RSA, PQC is built on brand-new algorithms that don't factor in tremendous semi-prime values.

What is the main advantage of quantum cryptography?

The main advantage of quantum cryptography is its ability to provide information-theoretic security. Unlike classical cryptography, which relies on computational assumptions, quantum cryptography offers provable security based on the fundamental principles of quantum mechanics or quantum mechanical properties. It provides a way to detect any unauthorized interception of the quantum states used for key exchange, ensuring secure communication.

How does cryptography work?

To understand how quantum cryptography works, let's explore the two primary methods used: quantum key distribution (QKD) and quantum-resistant encryption.

1. Quantum Key Distribution (QKD)

Quantum key distribution allows two parties, traditionally referred to as Alice (sender) and Bob (receiver), to establish a shared secret key over an insecure communication channel. The process involves the following steps:

Key Generation

Alice generates a series of individual photons, which are quantum particles of light. Each photon represents a qubit, which can be in multiple states simultaneously due to the principles of superposition and entanglement in quantum mechanics.


Alice randomly encodes each photon with one of four possible states: horizontal polarization, vertical polarization, diagonal polarization, or anti-diagonal polarization. Each polarization state represents a 0 or 1-bit value.


Alice sends the encoded photons, one at a time, to Bob through the insecure channel. However, due to eavesdropping, the channel may be compromised.


Upon receiving the photons, Bob randomly measures each one using a basis. The basis determines how the polarization is measured (e.g., horizontal/vertical or diagonal/anti-diagonal).


Alice and Bob publicly exchange the details of the basis used for each measurement without revealing the actual measurement results. They discard the measurements made with different bases.

Error Estimation

Alice and Bob compare a subset of their measurement results to estimate the error rate caused by noise and potential eavesdropping. If the error rate is within an acceptable range, they proceed; otherwise, they abort the process.

Privacy Amplification

Alice and Bob perform error correction and privacy amplification protocols to refine the shared key, eliminating any information an eavesdropper might possess.

Shared Key

After the protocols, Alice and Bob obtain a final shared secret key known only to them, which can be used for secure encryption and decryption.


The quantum key distribution provides security by exploiting the fundamental properties of quantum mechanics. Any attempt to intercept or eavesdrop on the photons would disturb their quantum states, causing detectable errors and alerting Alice and Bob to the presence of an intruder.

2. Quantum-Resistant Encryption

Quantum-resistant encryption is designed to withstand attacks from both classical and challenge quantum computers. While traditional encryption algorithms, such as RSA and ECC, are vulnerable to attacks by quantum computers, quantum-resistant algorithms offer enhanced security. These algorithms are designed and developed to be resistant to attacks based on Shor's algorithm, which can efficiently solve certain mathematical problems upon which many existing data encryption methods rely.


Quantum-resistant encryption algorithms typically employ mathematical problems that are computationally difficult for both classical and quantum computers to solve. Examples of quantum-resistant encryption algorithms include lattice-based cryptography, code-based cryptography, multivariate cryptography, and hash-based cryptography.


Here is a quick look at the quantum cryptography applications


Many business enterprises prefer to start deploying quantum cryptography solutions to amplify network and application security, especially in industries like:


  • BFSI (banking, financial services, and insurance),
  • defense
  • government
  • healthcare
  • automotive
  • and retail.


In summary, quantum cryptography leverages the principles of quantum mechanics, such as superposition, entanglement, and measurement, to provide secure communication. Quantum key distribution allows two parties to establish a shared secret key, while quantum-resistant encryption algorithms offer protection against attacks by both classical and quantum computers. These techniques together form the basis for securing sensitive information in the era of quantum computing.


1. Can quantum cryptography be hacked?

Ans: In theory, quantum cryptography is secure against any hacking attempts. However, like any other practical implementation, it is subject to certain limitations and vulnerabilities.

2. Is quantum cryptography widely used?

Ans: Quantum cryptography is still an emerging field, and its practical applications are relatively limited compared to classical cryptography. However, there has been progress in implementing quantum key distribution (QKD) systems for secure communication in certain domains, such as government communications, financial institutions, and critical infrastructure.

3. Are there any challenges or limitations to quantum cryptography?

Ans: Yes, quantum cryptography faces several challenges and limitations.

4. Can quantum cryptography be integrated with classical cryptography?

Ans: Yes, quantum cryptography can be integrated with classical cryptography to enhance overall security.


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