MATFYZ

Úvod do kryptografie

January 30 2023 [Edit]

stránka předmětu

• Basics
  • Kerckhaff’s principle

Basics

• Good cypher only leaks:
  • existence of communication
  • existence of message
  • size of a message

Primitives:

• Symmetric cipher encrypt and decrypt keys are same

$$\begin{align} \mathrm{E}&: \{0,1\}^{n} \times \{0,1\} \rightarrow \{0,1\}^{n} \\ \mathrm{D}&: \forall x \forall k: D \left( E \left(x,k\right),k\right) = x \end{align}$$

• Asymmetric cipher
• Hash function

$$h: \{0,1\}^{*} \rightarrow \{0,1\}^{k}$$

• not (quickly) invertible

• not be able to find collision

• Random number generator
• cannot be predicted
• nor influenced
• by the attacker nonce - number used once

Kerckhaff’s principle

Secret is in a key not in the algorithm.