Cryptography

1
Cryptography Steganography
235034 Security in Computer Systems and Networks

• Lec. Sanchai Yeewiyom
• School of Information and Communication
  Technology
• University of Phayao

2
Cryptography

• ??? ??????????????????????????????????????????????
  Sniffer ??????????????????
• ??????????????????????????????????????????????????
  ????? ????????????????????????????????????????????
  ?????????? ???????????????????????????????????????
  ? (Encrypt) ??????????????????????????????????????
  ??????? ??????????????????????????????????????
  (Decryption)

3
Cryptography
4
Cryptography ??????

• Caesar Cipher
• Ciphertext WKH TXLFN EURZQ IRA MXPSV RYHU WKH
  ODCB GRJ
• Plaintext the quick brown fox jumps over the
  lazy dog

5
Cryptography ??????

• Monoalphabetic Cipher
• Polyalphabetic Cipher ???????????????????????????
  ????????

6
Cryptography ??????

• One-Time Pad
• ??? Key ?????????? ??????????????????????? Plain
  Text ?????????????? Key ??????????
• Key ???????? Pad

7
Cryptography ??????

• Encrypt
• Decrypt

8
Cryptography
9
Cryptography

• ??????????????????????????????????????? 3 ??????
• Symmetric Key Cryptography (Secret Key
  Cryptography)
• Asymmetric Key Cryptography (Public Key
  Cryptography)
• Hash Function

10
Symmetric Key Cryptography

• ???????????????????????????????????????????????
  ??? ??????????????????????????????????????????????
  ?????????????????????????????

11
Symmetric Key Cryptography
12
Symmetric Key Cryptography

• ???????? 2 ?????? ???
• Stream Cipher
• Block Cipher

13
Stream Cipher

• ???????????? bit, byte ???? word
• ??????? Feedback ?????????? Key
  ??????????????????????????????

14
Stream Cipher
15
Block Cipher

• ????????????????????????????????
  ????????????????????????????
• Exp.
• Electronic Codebook (ECB)
• Cipher Block Chaining (CBC)

16
Electronic Codebook (ECB)

• Secret Key ???????????????? Block ??? Plain Text
  ???????????????? Block ??? Cipher Text
• ??????????? Block ??? Plain Text
  ?????????????????? Key ???????? ????????????????
  Block ??? Cipher Text ????????????
• ??????????????????????? ??????????????????????????
  ??????? Brute Force ???????

17
Electronic Codebook (ECB)
18
Cipher Block Chaining (CBC)

• ???????????? Feedback ????????????????????????
  Input ?????????????????
• ?? Plain Text ??????? Exclusive-OR (XOR) ???
  Cipher Text ??? Block ????????

A B X
0 0 0
0 1 1
1 0 1
1 1 0
19
Cipher Block Chaining (CBC)
20
A pixel-map version of the image on the left was
encrypted with ECB mode to create the center
image
Original
Encrypted using ECB mode
Encrypted using a more secure mode, e.g. CBC
21
Symmetric Key Cryptography Example

• Data Encryption Standard (DES)
• Triple-DES
• Advanced Encryption Standard (AES)
• Rivest Ciphers (RC)
• Blowfish

22
Data Encryption Standard (DES)

• ???????? IBM
• ??????????? Block Cipher
• ?????? Block ?? 64 bit ?????? Key ???? 56 bit
• ????????????????? ????????????????????????????????
  ??? ????????? Key ??????????

23
(No Transcript)
24
Triple-DES (3DES)

• ???????????????? DES ???????? 3 ???
• ??????? Key ??? 112 ???? 168 bit
• ??????????????????????????????????????

25
(No Transcript)
26
Advanced Encryption Standard (AES)

• ????????????????? National Institute of Standards
  and Technology (NIST) ????????????????????????????
  ???????????????????????
• ??????????? Block Cipher ????????? Block ?? 128,
  192 ???? 256 bit ?????? Key ???? 128, 192 ????
  256 bit

27
AES
28
Rivest Ciphers (RC)

• ????????? Ron Rivest
• ?????? Version
• RC4 ???? Stream Cipher ??????????????????????????
  Secure Socket Layer (SSL), Wired Equivalent
  Privacy (WEP) ??????? Key ????????
  ????????????????????????????????????????????????
  WEP
• RC6 ???? Block Cipher ?????????????? RC5
  ???????????? AES ????????? Block ?? 128 bit
  ?????? Key ???? 128, 192 ???? 256 bit
  ??????????????????????????????

29
Blowfish

• ????????? Bruce Schneier
• ???? Block Cipher ????????? Block ?? 64 bit
  ?????? Key ???? 32 - 448 bit ????? 16 ???
• ???????????????? CPU ??? 32 bit ????? Cache
  ????????
• ???????????????? DES
• ??????????????

30
Asymmetric Key Cryptography

• Public Key Cryptography
• ??????????????????????????????????????????????
• ????????????????????????????????????????
  ??????????????????????????????????????????????????
  ?????
• ????????????????????????????? 2 ??????????
  ???????????? (Public Key) ??? ????????????
  (Private Key)
• ??????????????????????????????????????????????????
  ??????????????????????????????????????????????????
  ??????????? ??????????????????????????????????????
  ?????????????????????????????????????

31
Asymmetric Key Cryptography
32
Asymmetric Key Cryptography

• ?????????????????????????????????????????????????
• ??????? ???? ?????? PGP (Pretty Good Privacy)
  ????????????
• ???????? E-mail ?????????????? Session Key
  (???????????????????
• ?????? Symmetric Key) ??????????????????????????
  Session
• Key ????????????????????????????????????????
  ??????
• ?????????????????????????????

33
Asymmetric Key Cryptography
34
Asymmetric Key Cryptography

• ??????????????????????????????? ????????????????
• ?????????????????????????????? Session Key
  ????? ???????????????? Session Key
  ???????????????????????????
• ????????????????????????????? Public Key
  Infrastructure (PKI) ????????????????? Key

35
Asymmetric Key Cryptography
36
Asymmetric Key Cryptography Example

• RSA
• Digital Signature
• Digital Certificate

37
RSA

• ??????????????.?. 2520 ??? ??? ??????? (Ron
  Rivest) ???? ?????? (Adi Shamir) ???????
  ????????? (Len Adleman)
• ?????????? Encryption ??? Digital Signature
• ????? Protocol ??????????????????????????
  (e-commerce) ???????????????????????? ??????? Key
  ????????
• ???????????????????????? Key ???? 1,024 bit

38
Digital Signature

• ????????????????????????????????????????
  (Authentication)
• ??????????????????????????????????????????????????
  ??????-?????????? (Data Integrity)
• ?????????????????????????????? ???????????????????
  ?????????????????????

39
Digital Signature (Authentication)
40
Digital Signature (Data Integrity)
41
Digital Certificate

• ?????????????????????????????????????? Public Key
  ??????????????????????????? ??????????????????????
  ???
• ????????????????????????????? Certificate
  Authority (CA) ?????????????????????? Public Key
  ?????????? ???????? Digital Certificate ???
• ?????????????????????? Website E-commerce
  ?????????????????????????
• ?????????????????? ?????? Cybertrust, VeriSign
  etc.

42
????????????????????????????????????? (CA)
???????????

• ?????????????? ??????
• 1. ??????????????????????????????????
• 2. ??????????????????????????????????????????????
  ????
• 3. ????????????????????????????????????
• 4. ???????????????????
• 5. Khonthai CA
• 6. ??????????????
• ???????????????? ??????
• 1. ?????? ?????? ????? (?????)
• 2. ?????? ??? ????????? ????? (?????)
• 3. ?????? ?????????? ???? ?????
• 4. ?????? Max Saving (Thailand) Co.,Ltd

43
Digital Certificate
44
Hash Function

• Hash Function ????????????? Oneway-encryption
  ????
• Algorithm ?????????????????????????? Key
  ????????????
• ???????? Plaintext ??????????????
  ????????????????????
• ??????????????????????????????????????
• Hash Function ??????????????????? Digital
  Fingerprint
• ?????????????? ???? Message Digest
  ?????????????????????
• ????????????????????????????????? Virus ???????

45
(No Transcript)
46
Hash Function

• ????? Operating System ????????????? Password
  ????? Login
• ???????????????????????????????? (Integrity)
• ???????????????? MD5, SHA-1

47
Hash Function Example

• Message Digest (MD)
• Secure Hash Algorithm (SHA)

48
Message Digest (MD)

• Message Digest ????????????????? Digest
  ?????????????
• ???????????????????????????? ?????????????????????
  ?????
• ??????????????????????????????????????????????????
  ???
• ??????????????????? ??????????????????????????????
  ?????
• ?????????????????????????? ????????????????????
• (Digest) ??????????? 128 ??? ?????????????????????
  ?????
• ?????????????????

49
Message Digest (MD)

• MD2
• MD4
• MD5

50
MD2

• ??????????? Ron Rivest ???????????????????????????
  ???
• ????????????????????????????????????? ??? Rivest
  ???????????
• ??????????????????????????????????????????????
  Digest
• ?????? MD2 ?????????????????????????????????
• MD2 ????? Digest ???????????? 128 ???

51
MD4

• ??????????? Rivest ???????????? MD2
  ??????????????????????
• ?????????????????????????????????????? MD2
  ?????????
• ??????????????????????????????????????????????????
  ????????
• ??????????????? 3 ???????????????
  (Availability) ??????
• ???????????????????????? Digest
  ?????????????????????
• ????
• MD4 ???? Digest ????????? 128 ???

52
MD5

• Rivest ????????????????????????????????? MD4
  ??????????
• ????????????????????? ????????????? MD4
  ?????????????
• ???????????????? ???????????????????????????
  ????????
• ?????????????????????????????????
  ???????????????????????
• ??? MD5 (???????????? MD4) ???????????????????????
  ??
• MD5 ???? Digest ????????? 128 ???

53
MD5
54
Secure Hash Algorithm (SHA)

• ?????????? SHA ??????????????????????????? MD4
• ?????????????????????????? National Security
  Agency
• (NSA) ?????????????????? Digital Signature
  ?????????????????
• ?????????????????????? Secure Hash Standard (SHS)
  ???
• NIST ??????????????????????
• SHA ????? Digest ????????? 160 ???

55
Secure Hash Algorithm (SHA)

• SHA-1
• SHA-256, SHA-384 ??? SHA-512

56
SHA-1

• SHA-1 ???? Algorithm ???????????????????
  ????????????????????????????? ????????????????????
  ??????????? ?????? Protocol ??????? ???? SSL
• SHA-1 ????? Digest ????????? 160 ???

57
SHA-1
58
SHA-256, SHA-384 ??? SHA-512

• NIST ????????????? Algorithm ?????????????? 2001
  ?????
• ????????????? Algorithm AES
• Algorithm ????????????? Digest ????????? 256, 384
  ???
• 512 ??? ????????

59
SHA-256
60
Steganography

• ????????????????????????????????????????????
  ??????????????????????????????????????????
  ????????????????????????? ???? ?????? ??????
  ?????? ????? ?????????????????????????????
• ????????????? Watermark

61
Steganography
62
Steganography

• ??????????????????????????????????? LSB (Least
  Significant Bit) ?????????????????????????????????
  ????????????????????????? (Picture, Sound, etc.)

63
Steganography
64
Steganography

• http//www.mobilefish.com/services/steganography/s
  teganography.php

65
Steganography

• Exp.
• OpenPuff 4.00 (http//embeddedsw.net/OpenPuff_Steg
  anography_Home.html)
• QuickStego (http//quickcrypto.com/free-steganogra
  phy-software.html)
• MP3Stego (http//www.petitcolas.net/fabien/stegano
  graphy/mp3stego/index.html)
• OurSecret (http//www.securekit.net/oursecret.htm)
  

66
Steganography

• ??????????????????????? ????????????? ????
• StegAlyzer (http//www.sarc-wv.com/)
• Stegdetect (http//www.outguess.org/detection.php)
  
• XStegSecret (http//stegsecret.sourceforge.net/)