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A group key, often referred to in the context of cryptography and secure communications, is a shared secret key used by a group of participants to encrypt and decrypt messages among themselves. This key enables secure communication within the group while allowing multiple users to share and access the encrypted information without needing separate keys for each pair of users.

HKDF, or HMAC-based Key Derivation Function, is a key derivation function that is based on HMAC (Hash-based Message Authentication Code). It is designed to be used to derive cryptographic keys or pseudorandom keys from a given input keying material. HKDF is defined in RFC 5869 and is notable for its robustness and simplicity.

HTTP Strict Transport Security (HSTS) is a web security policy mechanism that helps protect websites against man-in-the-middle attacks such as protocol downgrade attacks and cookie hijacking. HSTS enables a web server to declare that web browsers should only interact with it using secure HTTPS connections, rather than using unencrypted HTTP. Here's how HSTS works and its key features: 1. **Enforcement of HTTPS**: When a site implements HSTS, it informs browsers to enforce secure connections via HTTPS.

Hardware-based encryption refers to the process of encrypting data using dedicated hardware devices or components rather than relying solely on software-based implementations. This method utilizes specialized hardware to perform cryptographic operations, offering several advantages over software encryption, such as improved performance, enhanced security, and protection against certain vulnerabilities. Key features and aspects of hardware-based encryption include: 1. **Physical Security**: Hardware encryption devices can provide physical protection against tampering and unauthorized access, making it harder for attackers to extract sensitive information.

"Harvest now, decrypt later" typically refers to a cybersecurity strategy or an approach used by hackers. It involves collecting or harvesting sensitive data (like passwords or personal information) from various sources or systems while ensuring that the data is stored in an encrypted format. The idea is to capture this information swiftly during an attack and then decrypt it later when it might be more advantageous, such as when the attackers have more resources or when the data's value increases over time.

HashClash is a term primarily associated with a cryptographic attack involving hash functions, specifically targeting the SHA-1 (Secure Hash Algorithm 1) hash function. Researchers demonstrated that it is possible to generate two different sets of data that produce the same SHA-1 hash value, which is known as a hash collision. This discovery significantly weakened the security of SHA-1, as it allowed attackers to craft malicious files that could be indistinguishable from legitimate files in terms of their hash values.

Hashgraph is a distributed ledger technology that offers an alternative to traditional blockchain mechanisms. It was developed by Dr. Leemon Baird and is designed to provide a more efficient and scalable way to achieve consensus among distributed nodes in a network.

Honey encryption is a cryptographic technique designed to provide security against specific types of attacks on encrypted data, particularly chosen-plaintext attacks and brute-force attacks. The concept was introduced by Ran Canetti, Yuval Ishai, and Eyal Kushilevitz in 2016.

Human rights and encryption are interconnected concepts that address privacy, security, and freedom in the digital age. Here's an overview of each concept and their relationship: ### Human Rights Human rights are the fundamental rights and freedoms that belong to every person, regardless of nationality, sex, ethnicity, religion, or any other status. These rights are often enshrined in international law through documents such as the Universal Declaration of Human Rights (UDHR) adopted by the United Nations in 1948.

In cryptography, a **hybrid argument** typically refers to a methodology used to prove the security of cryptographic constructions, especially in the context of protocols that involve both symmetric and asymmetric cryptography. The hybrid argument is primarily used in the context of security proofs, particularly in regard to the security of cryptographic schemes against specific types of attacks.

A hybrid cryptosystem is a cryptographic system that combines the strengths of both symmetric and asymmetric (public-key) encryption to secure communications. This approach leverages the efficiency of symmetric encryption for bulk data encryption while using asymmetric encryption for secure key exchange. ### Key Features: 1. **Symmetric Encryption**: - Fast and efficient for encrypting large amounts of data. - Uses a single secret key for both encryption and decryption.

ISO/IEC 19790 is an international standard that provides a framework for the security requirements and evaluation of cryptographic modules. The standard outlines the criteria that cryptographic modules must meet to ensure their security and reliability in various applications, particularly in governmental and commercial sectors. ISO/IEC 19790 is designed to ensure that cryptographic modules achieve a high level of security by specifying requirements related to: 1. **Security Policy**: Defining a clear security policy for the cryptographic module.

Information leakage refers to the unauthorized transmission or exposure of sensitive information to individuals or systems that are not entitled to access it. This can occur in various contexts, including in computing, business, and data security. Here are a few key aspects of information leakage: 1. **Types of Information**: The leaked information can include personal data, corporate secrets, intellectual property, or classified government information.

Information security, often abbreviated as InfoSec, refers to the practices and processes designed to protect sensitive information from unauthorized access, disclosure, alteration, and destruction. Its primary goal is to ensure the confidentiality, integrity, and availability (often referred to as the CIA triad) of data, whether it is stored, processed, or transmitted. Key components of information security include: 1. **Confidentiality**: Ensuring that information is accessible only to those authorized to have access.

An **Initialization Vector (IV)** is a crucial component in cryptographic algorithms, especially in symmetric encryption schemes. It is a random or pseudo-random value that is used along with a secret key to ensure that the same plaintext encrypted multiple times produces different ciphertexts. This variability helps to enhance the security of the encryption.

KLJN Secure Key Exchange is a cryptographic protocol that aims to establish secure communication between two parties over an insecure channel. The name "KLJN" is derived from the initials of the last names of the protocol's inventors: Kolesar, Lentz, Johnson, and Nair. The KLJN protocol utilizes quantum key distribution (QKD) principles to create a shared secret key. It relies on the behavior of quantum bits (qubits), which can exist in multiple states simultaneously.

Kerckhoffs's principle is a fundamental concept in cryptography, formulated by Auguste Kerckhoffs in 1883. The principle states that a cryptographic system should be secure even if everything about the system, except the secret key, is public knowledge. In other words, the security of a cryptographic algorithm should not depend on the secrecy of the algorithm itself but rather on the secrecy of the key used within the algorithm.

A key-agreement protocol is a cryptographic method that allows two or more parties to securely establish a shared secret key over an untrusted communication channel. This shared key can then be used for encryption or authentication purposes in subsequent communications. Key-agreement protocols are vital in securing communications, especially in scenarios such as: 1. **Secure Communications**: Establishing a shared secret key for encrypting messages between two parties.

Keyring in the context of cryptography refers to a secure storage system for encryption keys, passwords, and other sensitive information. A keyring can take various forms, such as software applications, hardware devices, or managed services, and is designed to safeguard cryptographic keys that are essential for encrypting and decrypting data. ### Key Functions of Keyrings 1. **Storage**: Keyrings provide a secure repository for cryptographic keys, ensuring they are not easily accessible to unauthorized users.

Knapsack cryptosystems are a class of public-key cryptographic systems that are based on the mathematical problem of densely packed discrete sets, especially the subset-sum problem. They are named after the "knapsack problem," which is a well-known combinatorial optimization problem. ### Basic Concept The knapsack problem involves selecting a subset of items with given weights and values to maximize value without exceeding a certain weight limit. In the context of cryptography, the problem is generalized to integer weights.