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.
have been reported on COMP128 based on this leaked
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
One reported attack would require approximately 500,000 queries to
the SIM, which takes roughly 8 hours
Attacks are possible
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: