1. Mekanisme security & Crytography

8. Cryptography ≠Security Cryptography may be a component of a secure system Adding cryptography may not make a system secure

9. Basic Terminology plaintext - the original message ciphertext - the coded message cipher - algorithm for transforming plaintext to ciphertext key - info used in cipher known only to sender/receiver encipher (encrypt) - converting plaintext to ciphertext decipher (decrypt) - recovering ciphertext from plaintext cryptography - study of encryption principles/methods cryptanalysis (codebreaking) - the study of principles/ methods of deciphering ciphertext without knowing key cryptology - the field of both cryptography and cryptanalysis

10. Terms: types of ciphers restricted cipher symmetric algorithm public key algorithm

11. Restricted cipher Secret algorithm Leaking Reverse engineering – HD DVD (Dec 2006) and Blu-Ray (Jan 2007) – RC4 – All digital cellular encryption algorithms – DVD and DIVX video compression – Firewire – Enigma cipher machine – Every NATO and Warsaw Pact algorithm during Cold War

12. Symmetric algorithm Secret key C = EK(M ) M = DK(C )

13. Public key algorithm Public and private keys C1 = Epublic(M ) M = Dprivate(C1 ) also: C2 = Eprivate(M ) M = Dpublic(C2 )

14. Symmetric Cipher Model

15. Requirements two requirements for secure use of symmetric encryption: – a strong encryption algorithm – a secret key known only to sender / receiver Y = E K (X) X = D K (Y) assume encryption algorithm is known implies a secure channel to distribute key

16. Classic Cryptosystems

17. Substitution Ciphers

18. Jenis subtitution chipers

25. Caesar Cipher earliest known substitution cipher by Julius Caesar first attested use in military affairs replaces each letter by 3rd letter on example: meet me after the toga party PHHW PH DIWHU WKH WRJD SDUWB

26. Caesar Cipher can define transformation as: a b c d e f g h i j k l m n o p q r s t u v w x y z D E F G H I J K L M N O P Q R S T U V W X Y Z A B C mathematically give each letter a number a b c d e f g h i j k l m 0 1 2 3 4 5 6 7 8 9 10 11 12 n o p q r s t u v w x y Z 13 14 15 16 17 18 19 20 21 22 23 24 25 then have Caesar cipher as: C = E(p) = (p + k) mod (26) p = D(C) = (C – k) mod (26)

27. Ancient Hebrew variant(ATBASH) meet me after the toga party NVVG NV ZUGVI GSV GLTZ KZIGB

29. TABEL

31. Transposition Ciphers

32. Transposition ciphers: staff cipher

37. Secara Horisontal

42. Transposition cipher with key