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GSM Security Threats and Countermeasures Saravanan Bala Tanvir Ahmed Samuel Solomon Travis Atkison

GSM Security Threats and Countermeasures

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GSM Security Threats and Countermeasures. Saravanan Bala Tanvir Ahmed Samuel Solomon Travis Atkison. Outline. Introduction A5/1 algorithm Security & a ttacks Proposed Solution Hardware Enhancement Software Application Conclusion. Mobile Communication-GSM. - PowerPoint PPT Presentation

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Page 1: GSM Security Threats and Countermeasures

GSM Security Threats and Countermeasures

Saravanan BalaTanvir Ahmed

Samuel SolomonTravis Atkison

Page 2: GSM Security Threats and Countermeasures

Outline

Introduction

A5/1 algorithm

Security & attacks

Proposed Solution Hardware Enhancement

Software Application

Conclusion

Page 3: GSM Security Threats and Countermeasures

Mobile Communication-GSM

Most widely used cellular technology

Cryptographic Algorithms- A5/1, A5/2, A5/3

A5/1 Algorithm provides over the air privacy

Page 4: GSM Security Threats and Countermeasures

A5/1• GSM phone conversations:

sequences of frames.• One 228 bit = frame is sent in 4.6

milliseconds: 114 bits for the communication in each direction.

• A5/1 produces 228 bits to XOR with the plaintext in each frame

Page 5: GSM Security Threats and Countermeasures

A5/1 LFSRsConsists of 3 LFSRs of

different lengths

19 bits • x18 + x17 + x16 + x13 + 1

• clock bit 8 • tapped bits: 13, 16, 17,

18

22 bits • x21 + x20 + 1 • clock bit 10

• tapped bits 20, 21

23 bits • x22 + x21 + x20 + x7 + 1

• clock bit 10 • tapped bits 7, 20, 21, 22

Page 6: GSM Security Threats and Countermeasures

A5/1 - Clocking

Page 7: GSM Security Threats and Countermeasures

A5/1 clocking

Majority rule

m=maj(c1, c2, c3)

m=maj(1, 1, 0)

maj = 1

Registers R1 & R2

Page 8: GSM Security Threats and Countermeasures

Design Vulnerability

Design of Clock Controlling Unit

Linear Combination Function  

Page 9: GSM Security Threats and Countermeasures

Possible Attacks

Chosen plain Text attacks

Time memory trade off attacks

Correlation attacks

Page 10: GSM Security Threats and Countermeasures

Proposed Counter Measures

Hardware Enhancement

Software Application- Additional Encryption

Page 11: GSM Security Threats and Countermeasures

Hardware Enhancement

 

Page 12: GSM Security Threats and Countermeasures

Contd..

Enhanced Majority Rule

Computes two majority values

m1=maj(b1, b2, b3) m2=maj(c1, c2, c3)

Let S1 = { } and S2 = { } (Imaginary sets)

S1∩S2

Page 13: GSM Security Threats and Countermeasures

Contd..

Linear combining functions are cryptographically weak functions

Non Linear Combining Function

Combining function not fixed - changed dynamically by using a 2:1 multiplexer.

Page 14: GSM Security Threats and Countermeasures

Software Application

End to end encryption Encrypt speech signal at user end Solution includes using transmission of encrypted voice GSM

Data Call CSW Example : SecureGSM

Another solution includes usage of connection based packet switching. Example : Babylon nG

Both techniques use Diffie-Hellman key agreement protocol for ciphering key exchange and AES cipher for encryption of voice.

Experimentally proved that the implementation of AES cipher provides more robust and efficient system.

Page 15: GSM Security Threats and Countermeasures

 CONCLUSION

Proposed scheme generates cryptographically better key sequence than the current version of A5/1

Future mobile communications can be handled using UMTS

Page 16: GSM Security Threats and Countermeasures

REFERENCES

 [1]     “Secure Mobile Communication Using Low Bit-Rate Coding Method”. IEEE paper published by Wasif, M.; Sanghavi, C.R.; Elahi, M.; [2]     “Another attack on A5/1”. IEEE paper published by Patrik Ekdahl and Thomas Johansson.[3]     “Enhanced A5/1 Cipher with Improved Linear Complexity”. IEEE paper published by Musheer Ahmad and Izharuddin. [4]     “Introduction to the design & analysis of algorithms” by Anany Levitin.[5]     Based on the presentation given by Karsten Nohl on the “26th Chaos Communication Congress (26C3)” conference.[6]     “Security Enhancements in GSM Cellular Standard”. IEEE paper published by Musheer Ahmad and Izharuddin.[7]     “Communication Security in GSM Networks” published on 2008 international conference on security technology by Petr Bouška, Martin Drahanský.[8]     “Implementation and Analysis of AES, DES and Triple DES on GSM network” an IEEE paper published by Sachin and Dinesh kumar[9]     “Construction of nonlinear Boolean functions with important Cryptographic properties - Advances in Cryptology” by Sarkar and Maitra.[10] Diagram in slide number 6 taken from wikipedia.

 

Page 17: GSM Security Threats and Countermeasures

Questions ????

Page 18: GSM Security Threats and Countermeasures

Thank you all