1.  Advisor: Dr. Quincy Wu  Speaker: Hui - Hsiung Chung  Date: 2010-09-21 1

2.  WEP  RC4  How to Crack WEP  Reference 2

3.  WEP ◦ Wired Equivalent Privacy ◦ 64 bits and 128 bits ◦ 24 bits IV(Initialization Vector) ◦ 128 bits  26 hexadecimal characters or 13 ASCII characters ◦ 64 bits  10 hexadecimal characters or 5 ASCII characters ◦ CRC  WPA ◦ Wi-Fi Protected Access 3

4.  Rivest Cipher 4  Designed By Ron Rivest  RSA ◦ Ron Rivest ◦ Adi Shamir ◦ Leonard Adleman  KSA and PRGA 4

5.  KSA ◦ Key Schedule Algorithm 5 K[] =Key Array Initialization ： For i = 0 to N-1 S[i]=i j = 0 Scatter ： For i = 0 to N-1 j =j + S[i] + K[ i mod L ] Swap ( S[i], S[j] )

6.  PRGA ◦ Pseudo Random Generation Algorithm 6 Initialization ： i = 0 j = 0 Loop ： i = i + 1 j = j + S[i] Swap( S[i],S[j] ) Output: S[ S[i]+S[j] ]

7.  Cyclic Redundancy Check ◦ Based on Binary Division ◦ Calculate Data Checksum before Transmit,and then Check the Data is the same by Checksum after Transmit 7

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9.  Repeated Use the Key Stream  Small IV Value ◦ 2^24 = 1,677,216 ◦ Every 5134 Packets Happened Collision(Birthday Paradox)Birthday Paradox  IV Value is a Plain Text  Unreliable Checksum Value 9

10. 10 WEPWPA Key64-bits or 128- bits 128-bits Encryption Algorithm RC4 IV24-bits48-bits Key Management None802.1x

11.  IV Collision ◦ Collecting IV Packets ◦ Find Two Same IV Packets ◦ Use SNAP Header’s First Byte and XOR Operation to Find the KeySNAP 11

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14. 14  A wireless NIC with monitor mode AP channel

15. 15 APs Packets with IVs

16. 16 APs IVs Target AP

17. 17 Spending Time IVs

18.  WEP Encryption ◦ 64-bits  250,000 IVs  Less than 3 hours ◦ 128-bits  580,000 IVs  Less than 6 hours 18

19.  Scott Fluhrer, Itsik Mantin and Adi Shamir, Weaknesses in the Key Scheduling Algorithm of RC4, Selected Areas in Cryptography 2001, pp1 – 24  戴志坤, 楊中皇, 無線網路安全技術之分析與偵測分 析系統之設計與實現,TANET 2006  黃定宇、林韓禹、鄭家明、 葉義雄, Optimized WEP Protocol, NCS 2007 19

20.  What Probability Does Every Q(H) People Have the Same Birthday? ◦ Let Probability is 50% ( Collision Rate) ◦ Let H is equal to 365 ◦ Formula: ◦ Q(H):23.9 20 Back

21.  SubNetwork Access Protocol ◦ IEEE Defined ◦ Support the Coexistence of Multiple Standard on 802.2 LLC(Logical Link Control) 21 Physical Layer MAC LLC High-Level Protocol MAC LLC High-Level Protocol Back