7 Cryptography Interview Questions (With Sample Answers)

Updated 22 March 2023

Cryptography is a branch of computer science that uses mathematical concepts, and encryption- decryption algorithms to keep information secure and private. Government organisations, banks, non-banking financial corporations (NBFCs), fintech startups and other businesses that handle sensitive data use the principles of cryptography to protect their information from cybercriminals. Preparing for questions on cryptographic techniques, and practices can help you secure the best jobs in network and information security. In this article, we list a few cryptography interview questions, and sample responses that you can refer to while preparing for a security interview and review a list of tips to help.

7 Cryptography Interview Questions With Sample Answers

Here are a few cryptography interview questions that the hiring manager might ask:

1. How are cryptographic algorithms classified?

Cryptography uses different algorithms for various tasks, such as data encryption, digital signatures and authentication. The interviewer asks this question to determine if you know different types of cryptographic algorithms. In your answer, you can briefly explain the three types and provide a few examples for each. Sharing examples help to demonstrate your in-depth knowledge of the topic.

Example: Cryptographic algorithms are of three main types, including encryption, signature and hashing. Encryption algorithms like data encryption standard (DES), advanced encryption standard (AES) and RSA security encrypt data to provide confidentiality. Signature algorithms like the digital signature algorithm (DSA), elliptic curve digital signature algorithm (ECDSA) and Schnorr signature digitally sign data for authentication. Finally, hashing algorithms like MD5, SHA-1, SHA-2 and LANMAN provide data integrity.

2. Can you explain the working of the Diffie-Hellman (DH) algorithm?

Mathematicians and information security researchers have developed hundreds of cryptographic algorithms. While it is impossible to know all these, reviewing a few popular ones can help you confidently answer questions about them. In your answer, you can use examples to demonstrate your understanding of the algorithm and its implementation.

Example: The Diffie-Hellman (DH) algorithm enables two parties communicating via a public channel to share a mutual secret without unauthorised people interpreting it. For example, consider two parties, Ajay and Aditya. Both have a crucial piece of information that they wish to share while ensuring its secrecy. To do so, they mix publicly available information with their secret message and transmit it over the open channel.

The recipient deciphers the message using public information and the knowledge of their secret. While this algorithm appears simple, decryption by an outsider is mathematically infeasible as it uses long number strings for the public and private keys. As a result, this algorithm is highly secure, and makes it easy to send and receive secret messages over a public channel.

3. What is the difference between symmetric and asymmetric key encryption?

Hiring managers prefer candidates who have a strong understanding of cryptography basics. They ask fundamental questions like these to evaluate your theoretical knowledge of cryptographic principles. Structure your answer by sharing a brief definition of these encryption techniques and highlighting their key differences.

Example: In cryptography, encryption refers to concealing critical information to protect it from unauthorised readers. Both symmetric, and asymmetric encryption use keys to encrypt and decrypt data. The primary difference is that symmetric encryption uses the same key on both ends, while asymmetric encryption uses different keys for encrypting and decrypting data. The key size in symmetric encryption is 128 or 256 bits, whereas, in asymmetric encryption, it is 2048 bits or longer. As a result, symmetric encryption is faster than asymmetric methodology.

4. How would you explain private and public keys to non-security colleagues?

Irrespective of the role, and seniority cybersecurity experts often interact with employees from other teams and departments. The interviewer might ask this question to evaluate your communication skills, and determine if you can explain security challenges clearly and concisely to other employees. In your answer, you can describe the working of private and public keys using real-world analogies.

Example: Asymmetric cryptography, also known as public-key cryptography, is a specialised algorithm that helps two parties share and exchange information. It requires two pairs of keys, known as the public and private keys. You can think of the public key as a bank account number you can share with anyone. The private key is like the ATM pin known only to you. You can use the ATM pin, the private key, to log into your bank account and securely send money to the recipient by mentioning their account number, which is the public key.

The recipient uses their ATM pin, their private key, to validate access to their bank account and withdraw money. They identify who sent them the money, as your bank account number is mentioned in the transaction. Similarly, when you use private and public keys to share information, you ensure that only the intended recipient can read it by decrypting it with their private key. The recipient can identify the sender by verifying their public key. This algorithm helps two parties exchange information securely by encrypting and decrypting at both ends.

5. What is a ransomware attack and how would you protect the organisation against it?

This is a two-part question that requires you to know about ransomware attacks so that you can suggest efficient ways to safeguard organisational data. In your answer, you can briefly explain what it is and then list a few protection strategies to guard against ransomware attacks.

Example: Ransomware is malware that uses encryption techniques to lock the victim's digital assets. The hacker then demands a ransom, which is usually a large payment in cryptocurrency to restore access to the victim's files, databases and applications. The best way to avoid getting locked out of your critical files during a ransomware attack is to back up organisational data, preferably on an external hard drive away from the company's digital networks. This way, you can erase the compromised devices and reinstall files from the backup during a ransomware infection.

Other strategies to prevent, and mitigate ransomware attacks include using the latest anti-virus and security software, restricting access to critical company files from public networks. This activity can be clubbed with practising safe web browsing. I would also recommend conducting an organisation-wide security awareness training programme so that all employees are aware of phishing and other social engineering attacks and learn how to protect their systems and data.

6. Would you recommend using the MD5 hash to store user passwords?

The interviewer might ask tricky questions like these to evaluate if you know the latest news and trends in cryptography. Though MD5 hash was initially used to store passwords, it is no longer preferred as it is considered insecure. In your answer, you can explain why you would not choose MD5 and share better alternatives.

Example: No, I would not recommend MD5 as it is cryptographically broken. Instead, I would suggest using secure hash algorithms like the SHA-2 or SHA-3 as a safer and stronger method to store passwords.

7. Imagine you are the cryptography team lead and the organisation is under a digital attack, explain the steps you would take to handle the situation

The interviewer might pose hypothetical questions like these to evaluate your problem-solving and critical-thinking skills during a crisis. In your answer, you can provide a list of the recovery steps you would take to stop and mitigate the effects of a cyberattack.

Example: The first action I would do is to mobilise the cybersecurity response team to identify the type of attack. Once we understand what is happening, we can focus on how best to contain it. Then, I would instruct the team to immediately shut down the compromised access points to prevent further data loss. The next step would be to assess the damage and determine whether any other backdoors remain open. Finally, I would also ensure that we report the attack to the proper authorities, like the cyber crime department, and other state and national enforcement agencies.

Simultaneously, I would work with the PR department to determine how best to report the event to customers, vendors and the public. Finally, I would consider the event a learning opportunity, and thoroughly investigate the systems and applications to prevent similar attacks from reoccurring in the future. I would work with the rest of the cybersecurity team to implement more robust and secure cryptography techniques to better protect the organisational data.

Tips To Prepare For A Cryptography Interview

Here are a few tips to help you succeed in a cryptography interview:

Demonstrate practical communication skills. During the interview, you can use the situation, task, action, result (STAR) methodology to explain how your communication skills helped you overcome challenges in your previous roles.
Stay updated with the latest trends. You can mention the journals, research articles, and other sources that you use to keep your cryptographic skills updated and relevant in the workplace.
Structure your answers to align with the employer's requirements. Before the interview, read the job description carefully, understand the role's responsibilities, and duties and structure your answers to showcase your suitability for the position.

7 Cryptography Interview Questions (With Sample Answers)