Cryptography is the practice and study of techniques for secure communication and data protection in the presence of adversaries. It involves the use of mathematical algorithms to encrypt and decrypt information, ensuring confidentiality, integrity, and authentication in various digital processes and communications.

Cryptography is applied at all the mentioned areas in answers

The correct answer is Cryptanalysis

Cryptanalysis is the practice of analyzing and breaking cryptographic systems with the goal of gaining access to encrypted information without knowing the encryption key. It involves various techniques to exploit weaknesses in encryption algorithms or protocols.

Explanation of Incorrect Options:

1. Reverse engineering: This refers to analyzing a system to understand how it works, typically involving the deconstruction of code or hardware, but not specifically focused on cryptographic systems.
2. Tampering: This involves unauthorized modification of data or systems, but it is not specific to cryptographic systems.
3. Cryptobiosis: This is a biological term referring to a state of life in extreme environmental conditions, unrelated to cryptography or cryptanalysis.

A Cipher is a method or algorithm used in cryptography to encrypt or decrypt data. It involves the transformation of plaintext into Ciphertext (encryption) and vice versa (decryption) using a specific set of rules or mathematical operations.

All are different classic cipher methods. Hashing is a modern process in cryptography where a fixed-size string of characters (hash value) is generated from input data of any size.

Substitution is a classic cipher. It is a type of encryption where each letter in the plaintext is replaced with another letter according to a fixed rule or key. It involves substituting one set of symbols (usually letters) with another, providing a basic form of encryption.

Substitution is a classic cipher. It is a type of encryption where each letter in the plaintext is replaced with another letter according to a fixed rule or key. It involves substituting one set of symbols (usually letters) with another, providing a basic form of encryption.

A transposition cipher is a type of encryption where the positions of characters in the plaintext are rearranged based on a specific system or key. Instead of substituting characters, transposition ciphers involve changing the order of the characters to create the ciphertext.

A block cipher is a type of symmetric key algorithm used in cryptography that processes fixed-size blocks of data at a time. It encrypts or decrypts data in fixed-size blocks, typically 64 or 128 bits, using a secret key. The same key is used for both encryption and decryption in block ciphers.

A stream cipher is a type of symmetric key encryption algorithm used in cryptography. It encrypts data one bit or byte at a time, continuously streaming through the data. Stream ciphers use a key to generate a pseudorandom stream of bits, which is combined with the plaintext to produce the ciphertext. Unlike block ciphers, stream ciphers operate on individual bits or bytes rather than fixed-size blocks of data.

One-Time Pad  is  perfect encryption scheme that is considered unbreakable if Implemented properly. i.e:

1. The pad must be as long as the message.
2. The pad must be used only one time.
3. The pad must be made up of truly random values.
4. The pad must be securely distributed and protected at its destination.

Steganography is the practice of concealing one piece of information within another to hide the fact that communication is taking place. It involves embedding secret data within non-secret data, such as hiding messages within images, audio files, or other seemingly innocuous carriers. The goal is to make the presence of the hidden information undetectable.

The two main types of cryptography are:

Symmetric Key Cryptography:

1. Uses a single secret key for both encryption and decryption.
2. Faster than asymmetric cryptography but requires secure key distribution.

Asymmetric Key Cryptography (Public Key Cryptography):

1. Uses a pair of public and private keys.
2. Public key is used for encryption, and private key is used for decryption.

Facilitates secure communication without the need for a secure key exchange.

Symmetric cryptography is also called shared key cryptography because the same secret key is used for both encryption and decryption of the data. This key must be shared securely between the communicating parties before they can use it for secure communication. Since the key is shared between the entities involved, it is referred to as a shared key.

A public key is part of an asymmetric key pair used in public key cryptography. It is shared openly and used for encryption or verification by others, while the corresponding private key, kept secret, is used for decryption or signing.

DES, AES and IDEA are symmetric key algorithms. Using DES is not recommended

RSA, ECC and Elgamal are popular asymmetric algorithms while SHA is a hashing algorithm

Hashing is a process in cryptography where a fixed-size string of characters (hash value) is generated from input data of any size. It is a one-way function, meaning it is computationally infeasible to reverse the process and obtain the original input from the hash. Hashing is commonly used for data integrity verification, password storage, and digital signatures.

Integrity of data is ensured by hashing through the generation of a fixed-size hash value (digest) based on the content of data. If the data is altered in any way, even a minor change, the hash value will drastically differ. By comparing the computed hash value with the original hash, users can verify whether the data has been tampered with, providing a reliable mechanism for ensuring data integrity.

The correct answer is All mentioned here

A secure hashing function must meet all of the following requirements:

1. The input can be of any length and the output is fixed length: No matter the size of the input data, a hash function should always produce a fixed-length output (e.g., 256-bit output for SHA-256).
2. The hash function is one-way: A one-way function means it should be computationally infeasible to reverse the hash and retrieve the original input.
3. The hash function should be collision-free: It should be highly unlikely (ideally impossible) for two different inputs to produce the same hash output, i.e., no “collisions.”

The correct answer is Public Key Infrastructure (PKI)

Public Key Infrastructure (PKI) is a framework that enables secure and trusted communication between parties that may not have interacted before. It uses cryptographic techniques, primarily public and private keys, to provide authentication, encryption, and digital signatures, which help in securing communication and verifying the identity of parties.

Explanation of Incorrect Options:

1. Domain name services (DNS): This system translates domain names into IP addresses but does not establish secure, trusted communication.
2. Internet engineering task force (IETF): The IETF develops internet standards but does not directly facilitate secure communication between unknown parties.
3. Domain names registration service provider: These services register domain names but are not involved in secure communication.

Hashing algorithms can be applied to ensure the authenticity of messages by creating a fixed-size hash value (digest) from the message content. The sender shares or stores this hash value. Upon receipt or retrieval, the recipient computes a new hash value using the received or retrieved message. If the computed hash matches the original hash value, the message is considered authentic, as any alteration to the message content would result in a different hash value. Hashing is widely used for data integrity verification in secure communication and storage.