Subject: [Capwap] IEEE 802.11i - Encryption

From: "Saravanan Govindan" <[email-masked]>
Date: Fri, 3 Mar 2006 18:24:56 +0800

All,

For the IEEE 802.11 binding, the protocol deals with split-MAC and
local-MAC architectures. For both types, there is the design case of
having encryption at the WTP and authenticator at the AC. This design
case is a mandatory requirement from the Objectives. I think there was a
discussion about this in the last meeting. 

I suggest adding new Key Configuration & Key Configuration Response
messages to 11.8 "802.11 Control Messages" in the IEEE 802.11 bindings
section and describing the exchange in new subsections 11.8.4 to 11.8.5.

The suggested text follows;

----0000----

11.8.4      IEEE 802.11 Key Configuration

The IEEE 802.11 Key Configuration CAPWAP message is used in WTP designs
in which IEEE 802.11i authenticator functions are performed by the AC
and IEEE 802.11i cryptographic functions (encryption/decryption) are
performed by the WTPs. 

This CAPWAP message is sent from the AC to the WTP. It must contain
either of the following 2 message elements. 

 

11.8.4.1     IEEE 802.11 4-way Handshake

The IEEE 802.11 4-way Handshake message element is sent by the AC to the
WTP during the 4-way handshake. It contains Message-3 of the 4-way
handshake with unassigned values as the AC is unaware of the prevailing
KeyRSC sequence counter maintained by the WTP.  

Message-1, Message-2 and Message-4 of the 4-way handshake are
transported within CAPWAP data packets between AC and WTP. 

The IEEE 802.11 4-way Handshake message element contains the following
values:

      0                   1                   2                   3

      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     |    GTK-Flag   |                   Reserved                    |

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     |                        Encryption-Data                        |

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     |                          EAPoL-Frame                          |

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

GTK-Flag: An 8-bit flag that determines the type of KeyMIC calculation

     0 - New GTK, KeyMIC is calculated with KeyRSC = 0

     1 - Existing GTK, KeyMIC is calculated with prevailing KeyRSC value

Encryption-Data: Contains PTK and/or GTK

EAPoL-Frame: Contains Message-3 of 4-way handshake with unassigned
fields

Upon receipt of the Key Configuration message from the AC, the WTP
performs the following operations:

    i.            Assigns the corresponding value to the KeyRSC field of
the EAPoL-Frame 

ii.            Calculates KeyMIC with Encrytion-Data and KeyRSC

iii.            Updates Message-3 of 4-way handshake

iv.            Continues regular 4-way handshake with wireless terminals

 

11.8.4.2     IEEE 802.11 Group Key Handshake

The IEEE 802.11 Group Key Handshake message element is sent by the AC to
the WTP during the group key handshake. It contains Message-1 of the
group key handshake with unassigned values as the AC is unaware of the
prevailing KeyRSC sequence counter maintained by the WTP.  

Message-2 of the group key handshake is transported within a CAPWAP data
packet between AC and WTP. 

The IEEE 802.11 Group Key Handshake message element contains the
following values:

      0                   1                   2                   3

      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     |    GTK-Flag   |                   Reserved                    |

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     |                        Encryption-Data                        |

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     |                          EAPoL-Frame                          |

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

GTK-Flag: An 8-bit flag that determines the type of KeyMIC calculation

     0 - New GTK, KeyMIC is calculated with KeyRSC = 0

     1 - Existing GTK, KeyMIC is calculated with prevailing KeyRSC value

Encryption-Data: Contains PTK and/or GTK

EAPoL-Frame: Contains Message-1 of group key handshake with unassigned
fields

Upon receipt of the Key Configuration message from AC, the WTP performs
the following operations:

    i.            Assigns the corresponding value to the KeyRSC field of
the EAPoL-Frame 

ii.            Calculates KeyMIC with Encrytion-Data and KeyRSC

iii.            Updates Message-1 of group key handshake

iv.            Continues regular group handshake with wireless terminals

 

11.8.5     IEEE 802.11 Key Configuration Response

The IEEE 802.11 Key Configuration Response CAPWAP message is sent by the
WTP to the AC as an acknowledgement of the receipt of an IEEE 802.11 Key
Configuration Request. 

----XXXX----

Saravanan

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---

From: Michael Montemurro <[email-masked]>
Date: Fri, 3 Mar 2006 09:54:39 -0500

Saravanan,
 
It looks to me that some of this functionality is captured in the Add Mobile
message description in section 11.7.1.
Could you take a look at that section an suggest how it could be modified?
Or do you feel that we need to define a new message.
 
However I don't see what message would be used to transport a new GTK once
it has been generated by the AC.
 
Cheers,
 
    Mike

  _____  

From: Saravanan Govindan [mailto:[email-masked]] 
Sent: March 3, 2006 5:25 AM
To: [email-masked]
Subject: [Capwap] IEEE 802.11i - Encryption

All,

For the IEEE 802.11 binding, the protocol deals with split-MAC and local-MAC
architectures. For both types, there is the design case of having encryption
at the WTP and authenticator at the AC. This design case is a mandatory
requirement from the Objectives. I think there was a discussion about this
in the last meeting. 

I suggest adding new Key Configuration & Key Configuration Response messages
to 11.8 "802.11 Control Messages" in the IEEE 802.11 bindings section and
describing the exchange in new subsections 11.8.4 to 11.8.5.

 

----0000----

The IEEE 802.11 Key Configuration CAPWAP message is used in WTP designs in
which IEEE 802.11i authenticator functions are performed by the AC and IEEE
802.11i cryptographic functions (encryption/decryption) are performed by the
WTPs. 

This CAPWAP message is sent from the AC to the WTP. It must contain either
of the following 2 message elements. 

 

The IEEE 802.11 4-way Handshake message element is sent by the AC to the WTP
during the 4-way handshake. It contains Message-3 of the 4-way handshake
with unassigned values as the AC is unaware of the prevailing KeyRSC
sequence counter maintained by the WTP.  

Message-1, Message-2 and Message-4 of the 4-way handshake are transported
within CAPWAP data packets between AC and WTP. 

 

      0                   1                   2                   3

     |    GTK-Flag   |                   Reserved                    |

     |                        Encryption-Data                        |

     |                          EAPoL-Frame                          |

 

EAPoL-Frame: Contains Message-3 of 4-way handshake with unassigned fields

Upon receipt of the Key Configuration message from the AC, the WTP performs
the following operations:

    i.            Assigns the corresponding value to the KeyRSC field of the
EAPoL-Frame 

 

The IEEE 802.11 Group Key Handshake message element is sent by the AC to the
WTP during the group key handshake. It contains Message-1 of the group key
handshake with unassigned values as the AC is unaware of the prevailing
KeyRSC sequence counter maintained by the WTP.  

The IEEE 802.11 Group Key Handshake message element contains the following
values:

      0                   1                   2                   3

     |    GTK-Flag   |                   Reserved                    |

     |                        Encryption-Data                        |

     |                          EAPoL-Frame                          |

 

Upon receipt of the Key Configuration message from AC, the WTP performs the
following operations:

    i.            Assigns the corresponding value to the KeyRSC field of the
EAPoL-Frame 

 

The IEEE 802.11 Key Configuration Response CAPWAP message is sent by the WTP
to the AC as an acknowledgement of the receipt of an IEEE 802.11 Key
Configuration Request. 

----XXXX----

Saravanan

---

From: "Pat Calhoun (pacalhou)" <[email-masked]>
Date: Sat, 4 Mar 2006 15:28:25 -0800

Michael, the GTK is sent in the IEEE 802.11 Update WLAN.

Pat Calhoun
CTO, Wireless Networking Business Unit
Cisco Systems

________________________________

	From: Michael Montemurro [mailto:[email-masked]]

	Sent: Friday, March 03, 2006 6:55 AM
	To: Saravanan Govindan; [email-masked]
	Subject: RE: [Capwap] IEEE 802.11i - Encryption

	Saravanan,
	 
	It looks to me that some of this functionality is captured in
the Add Mobile message description in section 11.7.1.
	Could you take a look at that section an suggest how it could be
modified? Or do you feel that we need to define a new message.
	 
	However I don't see what message would be used to transport a
new GTK once it has been generated by the AC.
	 
	Cheers,
	 
	    Mike

________________________________

		From: Saravanan Govindan
[mailto:[email-masked]] 
		Sent: March 3, 2006 5:25 AM
		To: [email-masked]
		Subject: [Capwap] IEEE 802.11i - Encryption

		All,

		For the IEEE 802.11 binding, the protocol deals with
split-MAC and local-MAC architectures. For both types, there is the
design case of having encryption at the WTP and authenticator at the AC.
This design case is a mandatory requirement from the Objectives. I think
there was a discussion about this in the last meeting. 

		I suggest adding new Key Configuration & Key
Configuration Response messages to 11.8 "802.11 Control Messages" in the
IEEE 802.11 bindings section and describing the exchange in new
subsections 11.8.4 to 11.8.5.

		 

		----0000----

		The IEEE 802.11 Key Configuration CAPWAP message is used
in WTP designs in which IEEE 802.11i authenticator functions are
performed by the AC and IEEE 802.11i cryptographic functions
(encryption/decryption) are performed by the WTPs. 

		This CAPWAP message is sent from the AC to the WTP. It
must contain either of the following 2 message elements. 

		 

		The IEEE 802.11 4-way Handshake message element is sent
by the AC to the WTP during the 4-way handshake. It contains Message-3
of the 4-way handshake with unassigned values as the AC is unaware of
the prevailing KeyRSC sequence counter maintained by the WTP.  

		Message-1, Message-2 and Message-4 of the 4-way
handshake are transported within CAPWAP data packets between AC and WTP.

		The IEEE 802.11 4-way Handshake message element contains
the following values:

		      0                   1                   2
3

		      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4
5 6 7 8 9 0 1

		     |    GTK-Flag   |                   Reserved
|

		     |                        Encryption-Data
|

		     |                          EAPoL-Frame
|

		 

		GTK-Flag: An 8-bit flag that determines the type of
KeyMIC calculation

		     1 - Existing GTK, KeyMIC is calculated with
prevailing KeyRSC value

		EAPoL-Frame: Contains Message-3 of 4-way handshake with
unassigned fields

		Upon receipt of the Key Configuration message from the
AC, the WTP performs the following operations:

		    i.            Assigns the corresponding value to the
KeyRSC field of the EAPoL-Frame 

		ii.            Calculates KeyMIC with Encrytion-Data and
KeyRSC

		iv.            Continues regular 4-way handshake with
wireless terminals

		 

		The IEEE 802.11 Group Key Handshake message element is
sent by the AC to the WTP during the group key handshake. It contains
Message-1 of the group key handshake with unassigned values as the AC is
unaware of the prevailing KeyRSC sequence counter maintained by the WTP.

		Message-2 of the group key handshake is transported
within a CAPWAP data packet between AC and WTP. 

		The IEEE 802.11 Group Key Handshake message element
contains the following values:

		      0                   1                   2
3

		      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4
5 6 7 8 9 0 1

		     |    GTK-Flag   |                   Reserved
|

		     |                        Encryption-Data
|

		     |                          EAPoL-Frame
|

		 

		GTK-Flag: An 8-bit flag that determines the type of
KeyMIC calculation

		     1 - Existing GTK, KeyMIC is calculated with
prevailing KeyRSC value

		EAPoL-Frame: Contains Message-1 of group key handshake
with unassigned fields

		Upon receipt of the Key Configuration message from AC,
the WTP performs the following operations:

		    i.            Assigns the corresponding value to the
KeyRSC field of the EAPoL-Frame 

		ii.            Calculates KeyMIC with Encrytion-Data and
KeyRSC

		iv.            Continues regular group handshake with
wireless terminals

		 

		The IEEE 802.11 Key Configuration Response CAPWAP
message is sent by the WTP to the AC as an acknowledgement of the
receipt of an IEEE 802.11 Key Configuration Request. 

		----XXXX----

		Saravanan

---

From: "Saravanan Govindan" <[email-masked]>
Date: Mon, 6 Mar 2006 14:39:27 +0800

Hi Mike,

I should have read better!

Based on the Mobile Config Request message you pointed out (Section
11.7.1), an alternative to the suggestion below would be to include just
the message elements below;

- IEEE 802.11 4-way Handshake

- IEEE 802.11 Group Key Handshake

These message elements could then be used with the Mobile Config Request
message in cases where the WTP handles IEEE 802.11i
encryption/decryption and the AC handles the Authenticator functions.

Cheers,

Saravanan

 

From: Michael Montemurro [mailto:[email-masked]] 
Sent: Friday, March 03, 2006 10:55 PM
To: Saravanan Govindan; [email-masked]
Subject: RE: [Capwap] IEEE 802.11i - Encryption

Saravanan,

It looks to me that some of this functionality is captured in the Add
Mobile message description in section 11.7.1.

However I don't see what message would be used to transport a new GTK
once it has been generated by the AC.

Cheers,

    Mike

	From: Saravanan Govindan

	All,

	For the IEEE 802.11 binding, the protocol deals with split-MAC
and local-MAC architectures. For both types, there is the design case of
having encryption at the WTP and authenticator at the AC. This design
case is a mandatory requirement from the Objectives. I think there was a
discussion about this in the last meeting. 

	I suggest adding new Key Configuration & Key Configuration
Response messages to 11.8 "802.11 Control Messages" in the IEEE 802.11
bindings section and describing the exchange in new subsections 11.8.4
to 11.8.5.

	 

	----0000----

	The IEEE 802.11 Key Configuration CAPWAP message is used in WTP
designs in which IEEE 802.11i authenticator functions are performed by
the AC and IEEE 802.11i cryptographic functions (encryption/decryption)
are performed by the WTPs. 

	This CAPWAP message is sent from the AC to the WTP. It must
contain either of the following 2 message elements. 

	 

	The IEEE 802.11 4-way Handshake message element is sent by the
AC to the WTP during the 4-way handshake. It contains Message-3 of the
4-way handshake with unassigned values as the AC is unaware of the
prevailing KeyRSC sequence counter maintained by the WTP.  

	The IEEE 802.11 4-way Handshake message element contains the
following values:

	      0                   1                   2
3

	      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8
9 0 1

	     |    GTK-Flag   |                   Reserved
|

	     |                        Encryption-Data
|

	     |                          EAPoL-Frame
|

	 

	GTK-Flag: An 8-bit flag that determines the type of KeyMIC
calculation

	     1 - Existing GTK, KeyMIC is calculated with prevailing
KeyRSC value

	Upon receipt of the Key Configuration message from the AC, the
WTP performs the following operations:

	    i.            Assigns the corresponding value to the KeyRSC
field of the EAPoL-Frame 

	iv.            Continues regular 4-way handshake with wireless
terminals

	 

	The IEEE 802.11 Group Key Handshake message element is sent by
the AC to the WTP during the group key handshake. It contains Message-1
of the group key handshake with unassigned values as the AC is unaware
of the prevailing KeyRSC sequence counter maintained by the WTP.  

	Message-2 of the group key handshake is transported within a
CAPWAP data packet between AC and WTP. 

	      0                   1                   2
3

	      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8
9 0 1

	     |    GTK-Flag   |                   Reserved
|

	     |                        Encryption-Data
|

	     |                          EAPoL-Frame
|

	 

	GTK-Flag: An 8-bit flag that determines the type of KeyMIC
calculation

	     1 - Existing GTK, KeyMIC is calculated with prevailing
KeyRSC value

	EAPoL-Frame: Contains Message-1 of group key handshake with
unassigned fields

	Upon receipt of the Key Configuration message from AC, the WTP
performs the following operations:

	    i.            Assigns the corresponding value to the KeyRSC
field of the EAPoL-Frame 

	iv.            Continues regular group handshake with wireless
terminals

	 

	The IEEE 802.11 Key Configuration Response CAPWAP message is
sent by the WTP to the AC as an acknowledgement of the receipt of an
IEEE 802.11 Key Configuration Request. 

	----XXXX----

	Saravanan