[Resource Topic] 2002/068: Improved key recovery of level 1 of the Bluetooth Encryption System

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Improved key recovery of level 1 of the Bluetooth Encryption System

Authors: Scott Fluhrer


The encryption system (E_{0}), which is the encryption system used
in the Bluetooth specification, is a two level system where a key
and a packet nonce is given to a level 1 key stream generator, which
produces the key for a level 2 key stream generator, whose output is
used to encrypt.
We give a method for recovering the key for the level 1 key stream
generator given the internal keys for two or three
level 2 key stream generators. This method, combined with published
methods for recovering keys for the level 2 key stream generator,
can be used to recover the (E_{0}) second key with O(2^{65})
work, and O(2^{80}) precomputation time.

Although this attack is of no advantage if (E_{0}) is used with
the recommended security parameters (64 bit encryption key), it
shows that no addition security would be made available by enlarging
the encryption key, as discussed in the Bluetooth specification.

ePrint: https://eprint.iacr.org/2002/068

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