### Security

Unconditional (Information-theoretic)

The adversary is not able to solve the task even with infinite computing power

Probability theory, Information theory

Known unconditional secure crypto-systems

Conditional (Computational)

If the adversary is theoretically able to solve the task, but it is computationally infeasible

Computational complexity theory

No known computationally secure crypto-systems

Existence not formally proven

Easy

The computation can be done efficiently

Hard

The computation is not known to be feasible in an efficient way

Is not impossible that such an algorithm exists; it is just not known

### Semigroup

- Algebraic structure ⟨S, ∗⟩
- Nonempty set S

- Associativity axiom: ∀a,b,c ∈ S: a∗(b∗c)=(a∗b)∗c

(Associative binary operation ∗) - Closure Axiom: ∀a,b ∈ S: a∗b ∈ S

(S is closed)

### SNMP

Simple Network Management Protocol (SNMP) is an Internet-standard protocol for collecting and organizing information about managed devices on IP networks and for modifying that information to change device behavior. Devices that typically support SNMP include routers, switches, servers, workstations, printers, modem racks and more.

### SQL

SQL stands for Structured Query Language. SQL is used to communicate with a database. According to ANSI (American National Standards Institute), it is the standard language for relational database management systems.

### SQL Server

Microsoft SQL Server is a relational database management system developed by Microsoft. As a database server, it is a software product with the primary function of storing and retrieving data as requested by other software applications—which may run either on the same computer or on another computer across a network (including the Internet).

### Steganography

Methods of hiding the existence of a message or other data

### Subgroup

- Group
- A subset H of a group G is a subgroup of G if
- Is closed under the operation of G
- Also forms a group

### Symmetric Encryption System

Employs private key cryptography

Five components:

- A plaintext message space M
- A ciphertext space C
- A keyspace K
- A family E = {Ek :k∈K} of encryption functions Ek :M→C;
- A family D = {Dk :k∈K} of decryption functions Dk :C→M.

For every key k ∈ K and every message m ∈ M, the functions Dk and Ek must be inverse to each other (i.e., Dk(Ek(m)) = Ek(Dk(m)) = m).