[smb at cs.columbia.edu: Skype security evaluation]

[Ivars Suba]

Is it possible that Skype doesn't use RSA encryption? Or if they do, do
they do it without using any padding, and is that safe?
No ,Skype use RSA encryption:
"Each party contributes 128 random bits toward the 256-bit session key.
The contributions are exchanged as RSA cryptograms. The two
contributions are then combined in a cryptographically-sound way to form
the shared session key."
I.
-----Original Message-----
From: owner-cryptography at metzdowd.com
[mailto:owner-cryptography at metzdowd.com] On Behalf Of cyphrpunk
Sent: Monday, October 24, 2005 8:51 PM
To: Travis H.
Cc: cypherpunks at jfet.org; cryptography at metzdowd.com; berson at anagram.com
Subject: Re: [smb at cs.columbia.edu: Skype security evaluation]
X-Approval-Subject: BOUNCE cypherpunks at al-qaeda.net:    Non-member submission from ["Ivars Suba" <Ivars.Suba at bank.lv>]   

On 10/23/05, Travis H. <solinym at gmail.com> wrote:
> My understanding of the peer-to-peer key agreement protocol (hereafter
> p2pka) is based on section 3.3 and 3.4.2 and is something like this:
>
> A -> B: N_ab
> B -> A: N_ba
> B -> A: Sign{f(N_ab)}_a
> A -> B: Sign{f(N_ba)}_b
> A -> B: Sign{A, K_a}_SKYPE
> B -> A: Sign{B, K_b}_SKYPE
> A -> B: Sign{R_a}_a
> B -> A: Sign{R_b}_b
>
> Session key SK_AB = g(R_a, R_b)

But what you have shown here has no encryption, hence no secrecy.
Surely RSA encryption must be used somewhere along the line. The report
doesn't say anything about the details of how that is done. In
particular, although it mentions RSA signature padding it says nothing
about RSA encryption padding.

Is it possible that Skype doesn't use RSA encryption? Or if they do, do
they do it without using any padding, and is that safe?

CP

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