‘ƒ†¬»µ¹± ”¹„‰½ (...

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Ασφάλεια Δικτύων ( Computer Security ). Τι Εννοούμε με τον Όρο Ασφάλεια Δικτύων;. Ασφάλεια Μόνο ο αποστολέας και ο προοριζόμενος παραλήπτης μπορούν να διαβάσουν και να κατανοήσουν ένα μήνυμα. Ο αποστολέας το κρυπτογραφεί (encrypt) Ο παραλήπτης το αποκρυπτογραφεί ( decrypt ) . - PowerPoint PPT Presentation

Transcript of ‘ƒ†¬»µ¹± ”¹„‰½ (...

  • (Computer Security)

  • ; . (encrypt) (decrypt). (authentication) . (message integrity) .

  • :

  • (secrete key encryption) (public key encryption)

  • Packet Sniffing

  • IP Spoofing () ( ) .

  • (Denial of Service) (Distributed Denial of Service)

  • = : : ().

  • (substitution cipher) plaintext: abcdefghijklmnopqrstuvwxyzciphertext: mnbvcxzasdfghjklpoiuytrewqPlaintext: bob. i love you. aliceciphertext: nkn. s gktc wky. mgsbc ;

  • (Transposition Cipher) ;

  • (One-Time Pads) , .

  • (redundancy) . . (freshness)

  • (Data Encryption Standard DES)

  • DES.

  • (Advanced Encryption Standard). 128, 192 258 bits. . . Rijndael (Joan Daemen Vincent Rijmen).

  • : ;

  • () (Public Key Encryption) ( )

  • () e1( ) d2( )

    1 () 2 () e1( ) d2( )

    RSA: Rivest, Shamir, Adelson algorithm

  • RSA p, q (.., 1024 bits) n=pq z=(p-1)(q-1) e ( e
  • RSA (n,e) (n,d). m

  • Bob p =5, q= 7 n= pq= 35, z=(p-1)(q-1)= 24 e= 5 ( z) d=29 ( ed-1 z) : m=12, me= 1524832c= me mod n = 17 cd= 481968572106750915091411825223072000m= cd mod n = 12 =

  • (Message Digest) . , ,

  • Secure Hash Algorithm (SHA-1) 16 (words) WoW15 16 79, 5 04 04 i i+1

  • Bob Alice;

  • Bob Alice;

  • Bob Alice;I am Aliceencrypt(password)

  • R .

  • Second Session Bob Alice

  • Second SessionH Alice o Bob

  • , . (challenges) . .

  • Bob Alice ; .The Diffie-Hellman Key Exchange Alice (512-bit) xO Bob (512-bit) y 2 g n n (n-1)/2. H Trudy n, g, gx mod n, gy mod n, gxy mod n.

  • Trudy ; Alice xO Bob y Trudy z

  • (Key Distribution Center KDC) Alice Bob session key KS Trudy ; Trudy (KS(.)) (Replay Attack)Session Key

  • (Key Distribution Center KDC) Alice Bob session key KS Trudy ; Trudy (KS(.)) (Replay Attack) : Session Key

  • Needham-Schroeder Authentication

  • Otway-Rees Authentication

  • Kerberos Authentication

  • (Authenticity Certificates): Alice Bob;

  • () (Authenticity Certificates) Bob , , (Certification Authority) Bob . (Certification Authority CA) SHA-1

  • (Authenticity Certificates) Trudy Bob , Alice ! , SHA-1, . Trudy SHA-1 Bob

  • (Authenticity Certificates) (.., 18 ). 18 .

  • . Root;

  • Big Brother Bob P KBB(A, t, P). Alice, Bob BB(A, t, P) BB ( ) Alice;

  • Bob P D(P). Alice, Bob DA(P) Alice Alice. Alice;

  • Firewalls ;