Re: [Bluez-users] How to set the encryptions key size?

[Marcel Holtmann <marcel@holtmann.org>]

Hi Nina,

> is there a way to specify the encryption key size? Is it possible to
> enforce an encryption with a 128-bit key? I found out that there is a
> method to get the encryption key size, but I didn't find a way to set
> the key size.

the encryption key size can vary between 8-bit and 128-bit. Some chips
have a limited encryption key size of 56-bit, because of export
regulations in some country. For example for CSR chips you can use the
command "hciconfig hci0 revision" as root to check for the maximal
encryption key size.

In general the encryption key size is not changeable. However with chips
from CSR you can specify a range for it. Having a lower encryption key
size of 40-bit renders most devices useless, because the other side
won't accept any connection anymore.

So if your device has a maximum limit of 56-bit, this limit will be
hardcoded into the firmware in most cases and thus not changeable.

However the method to read the encryption key size of a piconet is
vendor specific. The Bluetooth SIG refuses to add a standard HCI command
for this task.

Regards

Marcel



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