Harbin Institute of Technology Shenzhen Graduate School. Cryptography ( 密碼學 ) 陳建銘 Chien-Ming Chen Ph. D. Assistant Professor

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1 Harbin Institute of Technology Shenzhen Graduate School Cryptography ( 密碼學 ) 陳建銘 Chien-Ming Chen Ph. D. Assistant Professor

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3 Outline Data Hiding Cryptography Key Management in Cryptography

4 Data Hiding

5 Data Hiding Data Hiding 資料隱藏 Steganography 藏匿學 Cryptography 密碼學

6 STEGANOGRAPHY( 藏匿學 ) 6

7 Steganography( 藏匿學 ) Physical wax tablet messenger's body invisible ink microdots

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11 Steganography( 藏匿學 ) 唐伯虎 西江月我聞西方大士, 為人了卻凡心 秋來明月照蓬門, 香滿禪房出徑 屈指靈山會後, 居然紫竹成林 童男童女拜觀音, 僕僕何嫌榮頓 內嵌 :[ 我為秋香屈居童僕 ]

12 Steganography( 藏匿學 ) 別氣節, 讓名冊, 勝登雅堂, 文人骨無存, 不想鴉片殺人身, 開燃有益, 心存漢奸志 別羞恥, 讓關說, 勝攫諸地, 文行建不農, 不視兒女兩三歲, 開戶自耕, 心念祖國風 別帝家, 讓妻籍, 勝戰守中, 文齒皆未通, 不顧龍馬皆期任, 開言戮諷, 心無感恩情 12

13 Steganography( 藏匿學 ) 13

14 Steganography ( 藏匿學 ) Digital photo, video, audio, etc.

15 CRYPTOGRAPHY ( 密碼學 ) 15

16 Cryptography Convert ordinary information into unintelligible gibberish Transposition Substitution zpvbsfbhppetqfblfs

17 Cryptography Transposition for example COW, CWO, OCW, OWC, WCO, WOC Scytale first mentioned in the 7th century BC

18 Cryptography Rail Fence cipher write message letters out diagonally over a number of rows then read off cipher row by row eg. write message out as: m e m a t r h t g p r y e t e f e t e o a a t giving ciphertext MEMATRHTGPRYETEFETEOAAT ncecipher.html

19 Cryptography Substitution Example 1: A B C D E X Y Plaintext: C A D E Ciphertext: Example 2: A B C D E X Y Z r z k a t b n s Plaintext: C A D E Ciphertext: k r a t

20 Cryptography Caesar cipher 58 BC

21 Cryptography Substitution: Caesar cipher Each letter is translated to the letter a fixed number of letters after it in the alphabet. Note: Julius Caesar only used a shift of 3. (Primitive Caesar Cipher) Caesar Cipher (general) c = (m) = (m + 4) mod 26 Plaintext m Cipher (m) Cipher (in lower case) A E e B F f C G g D H h E I i F J j... U Y y V Z z W A a X B b Y C c Z D d

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23 Cryptography Substitution: Caesar cipher Try to break this ciphertext zpvbsfbhppetqfblfs

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26 Monoalphabetic Cipher rather than just shifting the alphabet could shuffle (jumble) the letters arbitrarily each plaintext letter maps to a different random ciphertext letter hence key is 26 letters long Plain: abcdefghijklmnopqrstuvwxyz Cipher: DKVQFIBJWPESCXHTMYAUOLRGZN Plaintext: ifwewishtoreplaceletters Ciphertext: WIRFRWAJUHYFTSDVFSFUUFYA

27 Monoalphabetic Cipher Security now have a total of 26! = 4 x keys with so many keys, might think is secure but would be!!!wrong!!! problem is language characteristics Cryptography-Security Ch02-27

28 English Letter Frequencies

29 Monoalphabetic cipher: attack uzqsovuohxmopvgpozpevsgzwszopfpesxudbmetsxaizvuephzhm it a i e e te a that e e a i a t i e t dzshzowsfpappdtsvpquzwymxuzuhsxepyepopdzszufpombzwp ta t ha e ee a e ith i i a e e e ta i e the letter probability p 13.33% z 11.67% s 8.33% u 8.33% o 7.5% By statistics and guess: p e, z t, {s,u,o} {r,i,a,n,o,s} zw th, zwsz that, s a

30 Vigenere cipher Vigenere cipher (1585)

31 Vigenere cipher Vigenere cipher: an example Plaintext: ATTACKATDAWN Key: lemon Plain A T T A C K A T D A W N KEY L E M O N L E M O N L E cipher L X F O P V E F R N H R

32 Vigenere cipher KEY:SECURE plaintext JINGLE BELLS JINGLE BELLS JINGLE ALL THE WAY ciphertext BMPACITINFJNARIFVFWPNMAMFKNYRPDXJYNEQ 明文 J I N G L E B E L L S J I N G L E B E L L S J I N G L E A L L T H E W A Y 金鑰 S E C U R E S E C U R E S E C U R E S E C U R E S E C U R E S E C U R E S 密文 B M P A C I T I N F J N A R I F V F W P N M A M F K N Y R P D X J Y N E Q 32

33 Enigma Rotor machine The computer era Enigma Rotor machine adopted by Germany military and government during World War II.

34 DES DES (Data Encryption Standard) Designed by IBM selected by the NIST (National Institute of Standards and Technology) as an official FIPS (Federal Information Processing Standards) standard in 1976 Since the early 90's, theoretical attacks on the DES have been developed.

35 AES AES (Advanced Encryption Standard) NIST issued a request for possible candidates in Sept 1997 Submissions are due by June 15, /04/05 (5 candidate algorithms) Mars IBM (USA) RC6 RSADSI (USA) Rijndael V. Rijmen and J. Daemen (Belgium) Serpent R. Anderson et al. (UK, Israel, Norway) Twofish B. Schneier et al. (USA) 2000/10/02: Rijndael was selected as AES

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37 THE KEY PROBLEM!!!!!! 37

38 Key Problem Two ways to solve this problem Asymmetric cryptosystem Key agreement 38

39 Asymmetric Cryptosystem RSA Ron Rivest, Adi Shamir and Leonard Adleman Adi Shamir, Ron Rivest, Len Adleman 39

40 RSA 40

41 Key Management Diffie-Hellman key exchange published by Whitfield Diffie and Martin Hellman in

42 Key Management

43 Key Management Two party Three party Group Time-bound Etc.. 43

44 Q&A 44