Cryptography

A generic term used to describe the design and analysis of mechanisms based on mathematical techniques that provide fundamental security services.

A more precise term is 'Cryptology', which encompasses both the design(Cryptography) and analysis(Cryptanalysis) of these mechanisms.

Fundamentals of Cryptosystems

Cryptographic Primitives

Cryptographic Primitives is a Cryptographic process that provides a number of specified security services. If cryptography is a toolkit, then Cryptographic Primitives are the basic generic tools in that kit

Cryptographic Algorithms

A particular specification of a Cryptographic Primitive. A set of computational rules for implementation( e.g., AES for block ciphers).

Cryptographic Protocol

Sequence of message exchanges and operations among parties. They aim to achieve specific security goals, often by combining various cryptographic primitives. E.g., STS protocol (for key exchange), SSL/TLS (for secure web communication). If Cryptographic Primitives are tools, then a Cryptographic Protocol is a way of taking a number of these tools and using them in a specific way in order to achieve more complex security goals.

Cryptosystems

Refers to practical implementation of Cryptographic Primitives. It includes both cryptographic tools and the Infrastructure supporting them. The term is most commonly associated with systems used to ensure data confidentiality and may involve users, keys, management, and more.

Basic Model of a Cryptosystem

Misconceptions:

1. Encryption doesn't prevent interception - Encryption renders intercepted data unreadable without the decryption key, but it doesn't prevent data interception.

2. End-to-End confidentiality isn't guaranteed.

Steganography

Steganography is often confused with cryptography, but it has different underlying principles. Steganography focuses on information hiding.

• Main Aim: The primary goal is to transfer plain text from a sender to receiver in such a way that only receiver can extract plaintext. This is because only receiver knows that hidden plaintext exists and how to reveal it, such as by extracting information from a digital image.

• Unlike Cryptography, an interceptor may not even be aware that observed data contains hidden information.

Two Types of Cryptosystems

1. Symmetric Cryptosystems

2. Public Cryptosystems (Asymmetric)

Breaking Cryptosystems

The term 'Break' refers to the act of compromising or defeating the security of a cryptosystem. It means finding a way to decipher encrypted data or gain unauthorized access to protected data.

Two types of breaks:

1. Direct Decryption key determination

2. Weakness Exploitation