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

[cyphrpunk]

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