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
The computation can be done efficiently
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


  • 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)


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 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).


Methods of hiding the existence of a message or other data


  • 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).