COMP128

GSM Glossary

GSM — COMP128

 

 

 

 

 

 

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Information on COMP128

COMP128 is the default algorithm used by GSM network operators for authentication and key exchange. While the algorithm has never been officially released, information on its purported structure has been published on a number of web sites.
     Weaknesses that have been reported on COMP128 based on this leaked information include:

  • The structure of COMP128 has a structure related to the fast fourier transform. Such algorithms are known to have a number of common vulnerabilities.
  • The value of Kc generated by COMP128 is reported to be 54 bits. The 64-bit key required by the GSM A5 algorithm is generated by appending 10 zero bits.
  • The algorithm appears to have limited diffusion.

    •      One reported attack would require approximately 500,000 queries to the SIM, which takes roughly 8 hours
         Attacks are possible given either:
        
  • physical access to the SIM or
  • a rogue base station that authenticates mobiles in radio range.

    •      It is reported that a new algorithm, known as COMP128-2, is more secure.


    Other topics in our resources on GSM related to COMP128 include: 
     
  • GSM security
  • A3 authentication
    		•
  • A5 encryption
    		•
  • A8 key generation

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