Symmetric-key cryptography

Symmetric-key cryptography, also known as secret-key cryptography, is a type of encryption where the same key is used for both encryption and decryption of data. In this system, both parties involved in communication share a common key, which must remain confidential between them. ### Key Characteristics: 1. **Single Key**: Only one key is used for both encrypting and decrypting messages. This makes it efficient in terms of performance.

Authenticated encryption (AE) is a type of cryptographic scheme that combines both encryption and authentication to ensure the confidentiality, integrity, and authenticity of data. In other words, it not only encrypts the data to protect it from unauthorized access but also verifies that the data has not been tampered with and confirms the identity of the sender.

The "avalanche effect" refers to a phenomenon often discussed in cryptography and computer science, particularly in relation to hash functions and encryption algorithms. It characterizes how a small change to the input of a cryptographic function produces a significant and unpredictable change in the output.

A Bent function is a specific type of Boolean function that has maximum possible distance from all affine functions, making it highly nonlinear. In the context of cryptography and coding theory, Bent functions are particularly valued for their strong security properties and resistance to linear approximations, which makes them suitable for use in cryptographic applications.

In cryptography, **block size** refers to the size of the data blocks that a block cipher operates on during the encryption and decryption processes. A block cipher is a type of symmetric key cipher that encrypts data in fixed-size blocks, as opposed to stream ciphers, which encrypt data one bit or byte at a time. ### Key Points about Block Size: 1. **Fixed Length**: Block ciphers operate on data in blocks of a specific size.

Collision resistance is a property of cryptographic hash functions that ensures it is computationally infeasible to find two distinct inputs that produce the same hash output. In other words, for a hash function \( h \), it should be hard to find inputs \( x \) and \( y \) (where \( x \neq y \)) such that \( h(x) = h(y) \).

Confusion and diffusion are terms that can have various meanings based on context, including psychology, literature, and general usage. Here are brief explanations of both concepts in a few different contexts: ### Confusion 1. **Psychology**: In a psychological context, confusion refers to a state where an individual has difficulty understanding or making sense of information, often resulting in uncertainty or indecision. This can arise from cognitive overload, conflicting information, or emotional distress.

The Needham–Schroeder protocol is a classic authentication protocol for secure key exchange, designed to allow two parties to communicate securely over a network. It was proposed by Roger Needham and Michael Schroeder in 1978. The protocol is designed to ensure that both parties can authenticate each other and establish a shared secret key for encrypted communication.

The Otway–Rees protocol is a cryptographic key exchange protocol designed for secure communication between two parties, particularly in a networked environment. Developed by Michael Otway and Sarah Rees in the 1980s, the protocol is primarily focused on providing mutual authentication and establishing a session key for encrypted communication. Key characteristics of the Otway–Rees protocol include: 1. **Mutual Authentication**: The protocol ensures that both parties authenticate each other before establishing a secure communication channel.