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# Nonlinearity

(also nonlinear function or nonlinear system)

## Nonlinearity definition

Nonlinearity is a property of a system or function where the output is not directly proportional to the input. In the context of cybersecurity, nonlinearity often refers to cryptographic algorithms or encryption techniques that utilize nonlinear mathematical operations to increase the complexity of the encryption process and make it more resistant to attacks.

## Nonlinearity examples

• S-boxes: In symmetric-key cryptography, such as the Advanced Encryption Standard (AES), substitution boxes (S-boxes) are nonlinear components that replace input data with corresponding output data, adding complexity to the encryption process.
• Feistel networks: These are commonly used in block cipher algorithms and involve nonlinear functions that transform plaintext data into ciphertext.

## Nonlinearity vs. Linearity

Linearity is the opposite of nonlinearity, where the output is directly proportional to the input. Linear systems are typically easier to analyze and understand but can be less secure in the context of encryption, as they may be more susceptible to cryptanalysis.

## Pros:

• Increased security: Nonlinear encryption techniques provide stronger resistance to attacks.
• Enhanced complexity: Nonlinear operations make it more challenging for attackers to predict the output or reverse-engineer the algorithm.

## Cons:

• Higher computational requirements: Nonlinear algorithms often demand more processing power and resources, which may result in slower performance.