Subject: [AVT] Regading Replay Window- RFC 3711

From: [email-masked]
Date: Wed, 8 Jun 2005 18:24:23 +0530

Hi all, 

The RFC 3711 Section 3.3.2 indicates that the minimum SRTP-WINDOW-SIZE
is 64.

RFC states that "SRTP-WINDOW-SIZE is a receiver-side, implementation-
dependent parameter and MUST be at least 64, but which MAY be set to a
higher value. The Replay List can be efficiently implemented by using a
bitmap to represent which packets have been received, as described in
the Security Architecture for IP [RFC2401]."

In the RFC2401 Appendix C has the sample implementation for the
SRTP-WINDOW-SIZE of 32. For any higher value of window size this
implementation will fail. 

How we can implement a 64 or greater than 64 window size for a 32 bit
machine? Do we need to maintain more than one bitmap to achieve this? Or
is there any simple way?

Also is there any reason for having the window size has a minimum of 64?
Can we use minimum of 32 instead?

Many Thanks

Regards, 

Archana A

Work : 51052606

Mobile: 9880252553

_______________________________________________
Audio/Video Transport Working Group
[email-masked]
https://www1.ietf.org/mailman/listinfo/avt

---

From: "Karl Norrman (KI/EAB)" <[email-masked]>
Date: Wed, 8 Jun 2005 17:27:26 +0200

Hello!

If you want to implement a bitmap of 64 bits on a 32-bit machine
you can use two uint32_t to hold the bits, one for the first 32 and
the other for the remaining 32.  Then shift the bits through both 
the uint32_t:s.

An implementation with less than 64 bits window size would not be
compliant with the standard.  Note that packets that are "below" the
window are deemed as replayed (and are discarded), so the larger the 
window size, the more robust the implementation will be against
packets being delayed.

Regards,
Karl

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]On Behalf Of [email-masked]
Sent: den 8 juni 2005 14:54
To: [email-masked]
Cc: [email-masked]; [email-masked]
Subject: [AVT] Regading Replay Window- RFC 3711 

Hi all, 
 
The RFC 3711 Section 3.3.2 indicates that the minimum SRTP-WINDOW-SIZE is 64.
 
RFC states that "SRTP-WINDOW-SIZE is a receiver-side, implementation-   dependent parameter and MUST be at least 64, but which MAY be set to a higher value. The Replay List can be efficiently implemented by using a bitmap to represent which packets have been received, as described in the Security Architecture for IP [RFC2401]."
 
In the RFC2401 Appendix C has the sample implementation for the SRTP-WINDOW-SIZE of 32. For any higher value of window size this implementation will fail. 
 
How we can implement a 64 or greater than 64 window size for a 32 bit machine? Do we need to maintain more than one bitmap to achieve this? Or is there any simple way?
 
Also is there any reason for having the window size has a minimum of 64? Can we use minimum of 32 instead?
 
Many Thanks
Regards, 
Archana A
Work : 51052606
Mobile: 9880252553

---

From: "Hughes, James P" <[email-masked]>
Date: Wed, 8 Jun 2005 08:12:18 -0600

I do not know anything about SRTP. 

The sample code in just that, sample code. I consider the implemention of this to 64 bits to be QED. 

Thanks

Jim

-----Original Message-----
From: [email-masked] <[email-masked]>
To: [email-masked] <[email-masked]>
CC: Hughes, James P <[email-masked]>; [email-masked] <[email-masked]>
Sent: Wed Jun 08 06:54:23 2005
Subject: Regading Replay Window- RFC 3711 

Hi all, 

Many Thanks

Regards, 

Archana A

Work : 51052606

Mobile: 9880252553