full-disclosure - about uncovering skype

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Date: Wed Dec 28 16:46:50 2005
From: mis at seiden.com (mis@...den.com)
Subject: about uncovering skype

this may also interest you (and if you can find an archive of the
cryptography list, the followups which discuss the report and 
particularly the use of nonstandard key exchange).

Begin forwarded message:

From: "Steven M. Bellovin" <smb@...columbia.edu>               
Date: October 23, 2005 9:48:37 AM EDT
To: cryptography@...zdowd.com
Subject: Skype security evaluation

Skype has released an external security evaluation of its product; you                
can find it at http://www.skype.com/security/files/2005-031%20security
%20evaluation.pdf
(Skype was also clueful enough to publish the PGP signature of the
report, an excellent touch -- see
http://www.skype.com/security/files/2005-031%20security%
20evaluation.pdf.sig)
The author of the report, Tom Berson, has been in this business for many
years; I have a great deal of respect for him.

        --Steven M. Bellovin, http://www.cs.columbia.edu/~smb

On Wed, Dec 28, 2005 at 08:02:12PM +0800, ?????? wrote:
> HI:
>     i have recently read the paper <Skype uncovered>,and have some
> questions.In the part of UDP packet deciphering,the writer had mentioned
> that "The RC4 key is generated using src/dst IP plus packet ID",and in the
> figure the writer showed that we could use the src/dst IP plus packet ID to
> generate the crc32,but in the former page,there had alread been a
> crc32,so,where did it come from,and how should do to generate the correct
> crc32. Besides, for the src ip,if the client was behind a NAT,its src ip
> would be modified by the router when the packet pass out the NAT,and the
> receiver would see another src ip,so how could it generate the right rc4
> key?
>    Finally,can somebody show me the deciphered data of the example,i wonde
> if mine is right or wrong.
> 
> expecting for your reply.
> 
> Sincerely,
> Jiangxiao

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