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

## Presentation on theme: "GSM Security Threats and Countermeasures Saravanan Bala Tanvir Ahmed Samuel Solomon Travis Atkison."— Presentation transcript:

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

Outline  Introduction  A5/1 algorithm  Security & attacks  Proposed Solution  Hardware Enhancement  Software Application  Conclusion

Mobile Communication-GSM  Most widely used cellular technology  Cryptographic Algorithms- A5/1, A5/2, A5/3  A5/1 Algorithm provides over the air privacy

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

A5/1 LFSRs Consists of 3 LFSRs of different lengths 19 bits x 18 + x 17 + x 16 + x 13 + 1 clock bit 8 tapped bits: 13, 16, 17, 18 22 bits x 21 + x 20 + 1 clock bit 10 tapped bits 20, 21 23 bits x 22 + x 21 + x 20 + x 7 + 1 clock bit 10 tapped bits 7, 20, 21, 22

A5/1 - Clocking

A5/1 clocking  Majority rule  m=maj(c1, c2, c3)  m=maj(1, 1, 0)  maj = 1  Registers R1 & R2

Design Vulnerability  Design of Clock Controlling Unit  Linear Combination Function

Possible Attacks  Chosen plain Text attacks  Time memory trade off attacks  Correlation attacks

Proposed Counter Measures  Hardware Enhancement  Software Application- Additional Encryption

Hardware Enhancement

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

Contd..  Linear combining functions are cryptographically weak functions  Non Linear Combining Function  Combining function not fixed - changed dynamically by using a 2:1 multiplexer.

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.

CONCLUSION  Proposed scheme generates cryptographically better key sequence than the current version of A5/1  Future mobile communications can be handled using UMTS