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Authentication in wireless networks

Ludo Stoetenga

Chris van den Berg

Noordelijke Hogeschool Leeuwarden

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Introduction

Project Objectives Choices

– Network type– Standards

Types of Connections Encryption methods Conclusion

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Project Objectives

Investigate through documents and lecture studies about the subject and write a theoretical description about this.

Implement one of the encryption methods in a Java based environment.

Write a document how we implemented the authentications in Java.

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Choices

Network types– TTP (Trusted Third Party)– Location Limited– Chain of Thrust

Standards– 802.11b (Wi-Fi) – 802.16 (Broadband Wireless Metropolitan Area

Networks)

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TTP (Trusted Third Party)

A server that is trusted by the clients The server defines the protocol for secure

connections.

Client A

TTP

Client B

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Wireless

There are two standards

802.11 Wi-Fi Authentication

– Open Key– Shared Key

Encryption– RC4

802.16 MAN Authentication

– Open Key– Shared Key

Encryption– RSA– TripleDES

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Connections

Client connect with the TTP for the first time Client connect with a different Client

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Client connect with the TTP

Client TTP

Agree on secret key by Diffie-Hellman key agreement

Given a password (on a paper)

Send given password (encrypted with secret key)

Send new password (encrypted with secret key)

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Client connect with a different Client

Client A Client B

Get keys from the TTP encrypted with Shared Secret key

Send data encrypted with the keys provided by the TTP

TTP

Agree on Connection

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Encryption methods

Diffie-Hellman key agreement Lamport Scheme RSA RC4 TripleDES

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Diffie-Hellman key agreement

Gen X (0 > x > p-1)

Gen Y (0 > x > p-1)

A B

A and B agree on: P (prime) and G (1 > g > p)

Gx

Gy

A and B can both Compute Gxy

Gxy is the Shared secret Key

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Lamport scheme

Shared Secret Key

Key (40 bits)

One way function New Shared Secret Key

Shared secret key 40-bits key

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RSA

• 2 large primes P and Q• Compute N = P * Q and F = (P-1)(Q-1)• Select Random: E, 1 < E < F ( gcd(E,F)=1 )• Select Unique: D, 1 < D < F ( E * D = 1 (mod F)

• N modules• E Encryption exponent• D Decryption Exponent

A B

C = ME mod N

M = CD mod N

Send N, E

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RC4

A B

Shared secret Key

Encrypt Plain Text with Secret Key Cipher Text

Decrypt Cipher text with Secret Key

• RC4 uses a variable length key from 1 to 256 bytes

• The stream cipher uses swap and modulate operations to encrypt

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DES

Decryption is simply the inverse of encryption, following the same steps as above, but reversing the order in which the subkeys are applied. Blocksize is 64 bits

L0

R0

IP

InputL1

L0 + F(R0,key1)

L16

L15 + F(R15,key16)

FP

output

A B

Cipher Text

Encryption

Shared secret Key

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TripleDES

Triple-DES is just DES with two 48-bit key array’s applied in 3 rounds

Encrypt (key 1) Decrypt (key 2) Encrypt (key 1)

Decrypt (key 1) Encrypt (key 2) Decrypt (key 1)

Encryption

Decryption

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Conclusion

Encryption methods are not secure– Methods are insecure– Errors by programming

Standards– RC4– RSA– TripleDES