Bluetooth is a short-range wireless technology based off of a core specification that defines six different core configurations,including the Bluetooth Basic Rate/Enhanced Data Rate Core Configurations. Bluetooth BR/EDR is used for low-power short-range communications. To establish an encrypted connection,two Bluetooth devices must pair with each other and establish a link key that is used to generate the encryption key. For example,assume that there are two controllers attempting to establish a connection:Alice and Bob. After authenticating the link key,Alice proposes that she and Bob use 16 bytes of entropy. This number,N,could be between 1 and 16 bytes. Bob can either accept this,reject this and abort the negotiation,or propose a smaller value. Bob may wish to propose a smaller N value because he(the controller)does not support the larger amount of bytes proposed by Alice. After proposing a smaller amount,Alice can accept it and request to activate link-layer encryption with Bob,which Bob can accept. An attacker,Charlie,could force Alice and Bob to use a smaller N by intercepting Alice's proposal request to Bob and changing N. Charlie could lower N to as low as 1 byte,which Bob would subsequently accept since Bob supports 1 byte of entropy and it is within the range of the compliant values. Charlie could then intercept Bob's acceptance message to Alice and change the entropy proposal to 1 byte,which Alice would likely accept,because she may believe that Bob cannot support a larger N. Thus,both Alice and Bob would accept N and inform the Bluetooth hosts that encryption is active,without acknowledging or realizing that N is lower than either of them initially intended it to be.
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