[Cryptography] Cryptography 기본

정보보호 서비스의 특성 CIA Trial

1. Confidentiality(기밀성)

- keep close(= hiding infomation/unpermitted)

- Access control

- encrypt

2. Integrity(무결성)

- keep original data

- real/unreal 구분

3. Availability(가용성)

- use/useless 

- DDoS(Distributed Deniel of Service) attack form multical... (한꺼번에 왕창 server 공격)

CIA외에..

- authentication 인증

- non-repudiation 부인방지(cannot deny)(by evidence)

- permission 소원권

 

naming convention(암호에서 사용하는 이름)

Alice - sender (send message to Bob)

Bob - receiver (receive message from Alice)

Eve - shy/passive attacher, 도청

Mallory - active attacker, try to modify message, try to disconnect communication

Trent - trusted arbitrator (신뢰할 수 잇는 중재자) 

Victor- verified something, deny, proof

 

※ LAN

- Ethernet Link/Wired Network Card -> promiscuous mode (listen all data(같은 링크))

- Bus topology를 가짐 : (Alice -> Bob)상황에서 

                               other cannot send message or use the link

                               some listen communication

                               => 통신 중에 정보보호 필요성

※ http vs https

http://

https:// s의 의미는 secure, 전송 메시지 과부하하여 전송

※ phishing

Mallory의 message 수정 

- ex) phishing ( 일종의 hijacking )

 

ENCRYPTION 

원래 의미를 못 알아보도록 information shape 변경 

plaintext : original text message, not encrypted message

ciphertext : encrypted message

plaintext --(encrypt)--> ciphertext

 

DECRYPTION

ciphertext --(decrypt)--> plaintext

 

Cryptanalysis(암호해독)

- Another user(not the recepient) tries to break the cryptography, to translate ciphertext into plaintext

 

Components in cryptosystem

- plaintext

- ciphertext

- encryption algorithm

- decryption algorithm

- key

 

Symbols presentation in Cryptosystem(암호 시스템의 기호 표현)

C : Ciphertext , K : key , P : plaintext

Ek( ) : Encryption function , Dk( ) : Decryption function

C=Ek(P)=E(K,P) : Encrypt Plaintext with key, result in ciphertext

P=Dk(C)=D(K,P) : Decrypt Ciphertext with key, result in plaintext

 

 

 

 

 

★ Encryption, Decryption -> strong ...How?