# Cryptography Interview Questions & Answers

Cryptography is a burning topic for security professionals nowadays. This concept is responsible for securing digital data from adversaries. Here we will discuss interview questions and answers on cryptography that may be asked in your job interview.

**Q1. What is Cryptography?**

**Ans: **Cryptography is a process of hiding or securing information/data while transmitting, storing, and processing data by using different complex algorithms and methods.

**Q2. What is the goal of Cryptography?**

**Ans: **The goal of Cryptography is Confidentiality, Integrity, Availability, and Non-Repudiation of sensitive data flowing and stored in the IT system.

**Q3. What is the importance of Cryptography?**

**Ans: **As we move towards the digital economy, cryptography plays a crucial role in securing your digital assets from hackers by encrypting them.

**Q4. What are Ciphers?**

**Ans: **Cipher is a process of creating data in a non-readable form. In other words, you can say it is an algorithm responsible for the encryption and decryption of data.

**Q5. What are the different types of Ciphers?**

**Ans:** I am listing some ciphers below:

- Mono-alphabetic Ciphers
- Polyalphabetic Ciphers
- Transpositions and Grills
- Steganography
- Codes
- Voice Scramblers
- Modern Ciphers

**Q6. What is RSA in the field of Cryptography?**

**Ans:** RSA (Rivestâ€“Shamirâ€“Adleman) is an asymmetric cryptographic algorithm. It consists of two keys: Public and Private keys. The Private key holds only by the owner of that key, and the corresponding public key is available to different persons. If encryption is happening with the private key, decryption can be done with the public key, and vice versa depending on the usage of asymmetric encryption.

**Q7. How fast is RSA?**

**Ans:** RSA is asymmetric encryption, so it is definitely slow compared to symmetric encryption, such as DES. On average, DES is approximately 100 times faster than RSA.

**Q8. What is the major difference between the Symmetric and Asymmetric Key Algorithm?**

**Ans:** The major difference between the Symmetric and Asymmetric Key algorithms is using the same key in the case of the Symmetric Key algorithm while using different keys (public and private key) in the case of the Asymmetric Key Algorithm.

**Q9. What are Transposition Ciphers?**

**Ans: **Transpositional ciphers is an encryption algorithm based on rearranging letters of the original message and converting it into a non-readable form.

**Q10. What are the advantages of the Symmetric Key Algorithm?**

**Ans: **The main advantage of the Symmetric Key Algorithm is the fast speed of encryption in comparison with the Asymmetric Key Algorithm. Another important advantage of this algorithm is the property of extreme security that makes it unbreakable.

**Q11. What is a Running Key Cipher?**

**Ans:** Running key cipher is also called book cipher. In this cipher, the cipher's length is of the same length as of the original message. Here, both the sender and receiver agree to use the same chapter of the same book to encrypt and decrypt the message.

**Q12. What is Block Cipher?**

**Ans: **Block cipher is a method of encrypting data using cryptographic keys and algorithms to apply to a block or chunks of the message simultaneously rather than individually. The transposition cipher, AES, DES, 3DES, Twofish are examples of a Block cipher.

**Q13. What is Stream Cipher?**

**Ans: **In this cipher, the cryptographic algorithm is used to encrypt or decrypt a message one bit or character at a time. Here, stream ciphers encrypt data byte by byte. The Caesar cipher is an example of the stream cipher.

**Q14. List out different types of encryption algorithms.**

**Ans: **Currently many cryptographic algorithms are available to secure data. Some of them I am listed below:

- DES/3DES
- Blowfish
- AES
- MD5
- RSA

**Q15. List down some Hashing Algorithms.**

**Ans:** Hashing algorithms are used to convert data of any length into fixed-size hash values. I am listing some hash algorithms:

- Message Digest (MD)
- Secure Hash Function (SHA)
- RIPEMD
- Whirlpool

**Q16. What is the Data Encryption Standard (DES)?**

**Ans: **DES or Data Encryption Standard is a symmetric-key algorithm to encrypt data into a non-readable form. DES uses the same key of size 56 bits to encrypt and decrypt data.

**Q17. What is Triple DES (3DES)?**

**Ans: **Triple-DES is a type of symmetric-key algorithm and uses 168 bits keys (three 56 bits keys) to encrypt or decrypt a message. It is considered a strong algorithm than DES.

**Q18. What is the International Data Encryption Algorithm (IDEA)?**

**Ans: **International Data Encryption Algorithm (IDEA) algorithm is a symmetric-key block cipher that operates on 64-bit blocks using a 128-bit key.

**Q19. What is the Cryptographic Life Cycle?**

**Ans: **Cryptographic Life Cycle suggests an idea of the lifespan of any cryptography algorithm. As the enhancement of computing power increases day by day, it is easy for processors to guess cryptographic keys. Security professionals are working diligently to identify these algorithms' life cycles and suggest suitable replacements when needed by an organization.

**Q20. What is the Advanced Encryption Standard (AES)?**

**Ans: **Advanced Encryption Standard (AES) is a symmetric key block cipher used to encrypt and decrypt messages.

**Q21. What boolean logical operator ****played** is a critical role in cryptography?

**played**is a critical role in cryptography?

**Ans:** XOR played a critical role and is widely used in cryptography. It is also used in generating parity bits for error checking and fault tolerance.

**Q22. What is a One-Time Pad?**

**Ans:** One-Time Pad is a secret key that is used to encrypt and decrypt a message. Here, a secret key is used only once.

**Q23. What is ECB mode?**

**Ans:** ECB stands for Electronic CodeBook. It is the simplest mode of operation in the block cipher. Here, each plain block is encrypted independently to produce a ciphertext block. For the same plain block, the ciphertext block will remain the same.

**Q24. What are MACs?**

**Ans:** MACs stands for Message Authentication Codes. It helps in ensuring the integrity of data.

**Q25. How do** **passwords store securely on the server?**

**Ans:** It is recommended to use the BCrypt package to store passwords on the server. In addition, MD5 is strongly discouraged the use of storing passwords on database servers.

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**Disclaimer:** This tutorial is for educational purpose only. Individual is solely responsible for any illegal act.

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