1. Encrypting Management Frames
March 2003
Encrypting Management Frames
Mike Moreton
Synad Technologies Ltd.
Mike Moreton, Synad Technologies Ltd.

2. March 2003
doc.: IEEE /xxxr0
March 2003
Background
This submission discusses methods in which some management frames could be encrypted.
It doesn’t discuss why you would want to do that.
It doesn’t discuss which frames you might want to encrypt.
It doesn’t discuss how you would get the key, and how you would choose which cipher suite to use.
It’s just looking at techniques that could be used in other proposals.
Mike Moreton, Synad Technologies Ltd.
Mike Moreton, Synad Technologies Ltd.

3. Frame Control field includes the WEP bit
March 2003
Management frames use the same header as data frames (without the Address4 field).
Frame Control field includes the WEP bit
indicates if frame is encrypted.
All management frames have a payload. Encrypt it just like a data payload.
Problem : MIC does not cover frame sub-type – would need to change it to do this for non-data frames.
Frame Control
Duration/id
Address 1
Address 2
Address 3
Sequence Control
Address 4
Frame Body
Mike Moreton, Synad Technologies Ltd.

4. Would Legacy Hardware Support This?
March 2003
Would Legacy Hardware Support This?
Likely implementations of receiving are:
WEP bit determines whether to decrypt or not, ignore the frame type. OK
WEP bit ignored for non-authentication management frames. OK as we can decrypt in software
Likely implementations for transmitting are similar.
There are possible hardware implementations that would have problems, but I haven’t heard of any yet.
Mike Moreton, Synad Technologies Ltd.

5. Alternative Solution - Encapsulation
March 2003
Alternative Solution - Encapsulation
Don’t use the WEP bit to indicate encryption, instead have a type of action frame that always has an encrypted payload.
No legacy hardware problem as encryption/decryption is always in software.
Mike Moreton, Synad Technologies Ltd.

6. MAC Header (type = Action)
March 2003
MAC Header (type = Action)
Category (TGi)
Action (1)
Encapsulated Frame
FCS
CCMP Header
Frame Control
Frame Body
MIC
MIC must be extended to cover Category and Action fields as well as the usual parts of the MAC header.
2nd Frame Control field has fields other than type and subtype zeroed.
Receiver must forward the entire frame to software.
If you don’t
Mike Moreton, Synad Technologies Ltd.