[Information Processing Technician Practical] 3rd session in 2021 Key content (1)

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? Java singleton pattern output value

Create a Connection object in the main function.
When defining an object with get(), _inst initially creates a new object with a null value.
However, after that, the objects of conn2 and 3 are the same objects as the object of conn1, and the value is increased by 1 every time the count() method is performed, so they have the value of 3.
The memory allocated in the singleton pattern is the same.

싱글톤 패턴? is a design pattern in which a class allocates memory only once when an application starts and then creates an instance in that memory and uses it.

? Information Security Technology AAA

AAA stands for Authentication, Authorization, Accounting.

Authentication Verifies the identity of the user attempting to access the system before accessing the system.
Authorization grants a certain level of authority and service to verified users.
Collects usage information about users' resources (time, information, location, etc.) and manages accounts

? GRANT

One of the data control languages (DCL).

Command used to grant privileges to database users.

Data manipulation language DML ➡ SELECT, INSERT, UPDATE, DELETE
Data definition words DDL ➡ CREATE, ALTER, DROP, RENAME, TRUNCATE
Data control word DCL ➡ GRANT
Transaction control language TCL ➡ COMMIT, ROLLBACK, SAVEPOINT

? Spoofing

ARP spoofing

It is a man-in-the-middle attack technique that uses ARP messages under a local area network to intercept the other party's data packets. This attack uses ARP, a protocol on a data link, so it can only be used in short-distance communications.

IP spoofing

Exploiting vulnerabilities in IP's own security. You can also spoof your IP address to connect and then launch a DoS attack. A hacking technique that pretends to be a legitimate user to access another computer.

DNS spoofing

Taking control of the DNS server that connects the domain to the IP address, or sniffing the traffic in between and manipulating it to go to the IP address set by the attacker.

? Coupling

Modules in procedural programming refer to statements that contain subroutines.

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Control coupling

This is a coupling diagram when one module communicates using control signals for the purpose of controlling the internal logical organization of another module. A right conduction phenomenon may occur where a control signal moves from a lower module to a higher module and gives a processing command to the higher module.

+ Cohesion is Cohesion

? OSI 7 Layer

네트워크에서 통신이 일어나는 과정을 7단계로 나눈 것이다.

Layer 1 - Physical Layer

Communication cable, repeater, hub

Data is transmitted by converting it into an electrical signal. Communication units are bits, 1 and 0.

Layer 2 - Data Link Layer DataLink Layer

A role that helps ensure safe information delivery by managing errors and flows of information transmitted and received through the physical layer.

Bridges, switches, Ethernet

Mac address Communication using Mac address

Data unit is frame

Layer 3 - Network Layer Network Layer

Routing, a function that delivers data to its destination most safely and quickly

router, addressing, routing

Data unit is packet

Layer 4 - Transport Layer Transport Layer

Perform error detection and recovery, flow control and redundancy check

TCP, UDP

Data unit is segment

Layer 5 - Session Layer Session Layer

Interaction and synchronization between communicating devices

Manages data exchange in connection sessions and recovery in case of errors

Layer 6 - Presentation Layer

A layer responsible for deciding how to express data

Encoding, transformation, compression, encryption and decryption of data

Layer 7 - Application Layer Application Layer

Interface role, responsible for exchanging information between application processes

? 객체지향 연관성 or 관계성

It refers to a method of expressing an object and a class or a cross-reference relationship between classes in an object-oriented language.

Association

is-member-of

Reference and use relationship between classes and objects, meaning that they are interrelated, link

Classification

is-instance-of

Represents instances of objects and classes

Objects with the same type of characteristics come together to form a class.

Aggregation

is-part-of

Representing relationships between classes, such as whole or partial

Create a single parent object by combining multiple related objects

Used as a means of creating a user-defined entity by combining multiple properties

Generalization Generalization, Specialization Specialization

is-a

Define the common properties of objects as high-level objects and define specialized properties as low-level objects.

? Test case components

identifier id	test items	test conditions	test data	expected result
DS-45S-21	Login function	User initial screen	User ID, password	Login successful

? 테스트 기법

It can be broadly divided into white box testing and black box testing.

White box testing

Test all internal logical paths to design test cases and check logical paths

Basic path check
Control structure inspection ➡ Condition inspection, loop inspection, data flow inspection

Black box test

It is implemented in the interface, and there is no way to know what happens inside the module.

Equivalence split test A method of equally determining valid input data and invalid values for the input conditions as test cases and checking whether the results are output correctly.
Boundary value analysis: Boundary values are selected as test cases and inspected using the fact that errors are more likely to occur at boundary values than at the median of the input conditions.
Cause-effect graph inspection A method of systematically analyzing the relationships between input data and situations affecting the output and then selecting and inspecting highly effective tests.
Comparison test: Test multiple versions of a program with the same values
Error prediction test: Test to supplementally check errors that cannot be confirmed by other tests.

? 암호화 알고리즘

Symmetric key encryption method, secret key, private key ➡ Bidirectional

Use the same key for encryption/decryption

Block cipher DES, 3DES, SEED, AES, ARIA, IDEA DES Former US standard private key encryption algorithm 56-bit key SEED Developed by the Korea Internet & Security Agency AES Private key encryption algorithm announced by the American Institute of Standards and Technology Developed by the National Intelligence Service after ARIA SEED
Stream cipher RC4

Asymmetric key encryption method, public key ➡ two-way

What was encrypted with K1 is decrypted with K2, and what was encrypted with K2 is decrypted with K1.

Factorization: RSA, Rabin RSA was created based on the fact that large numbers are difficult to factor into prime numbers, proposed in 1978
Discrete logarithms: Diffie-Hellman, Elgamal, DSA, Schnorr
Elliptic curve: ECC

Hash Algorithm ➡ One-way

This means converting input data or messages of arbitrary length into values or keys of fixed length.

SHA, MD

Domestically developed encryption algorithm

ARIA, HIGHT, LEA, SEED

Source: https://q.fran.kr/%EC%8B%9C%ED%97%98/%EC%A0%95%EB%B3%B4%EC%B2%98%EB%A6%AC%EA%B8%B0%EC%82%AC%20%EC%8B%A4%EA%B8%B0/2021%EB%85%84%203%ED%9A%8C