Unleashing 10-User Conferencing in Skype 2.0 for Windows

Recently, Skype and Intel have announced a deal that would limit Skype's functionality on all but specific Intel processors. Currently, Skype 2.0 offers 10-way conference calls only on Intel's latest dual-core CPUs, while other chips, including all AMD chips, will only allow for 5-way conference calls. It is argued that only those Intel dual-core CPUs meet the requirements - which would imply that no AMD CPU is fast enough.

Now, what are these requirements? Is there some kind of micro-benchmark built into Skype which measures the processing speed? Or does Skype look for a specific hidden CPU feature? As the details on the patch reveal, the code logic behind the limitation is quite simple:

If it's a CPU with "GenuineIntel" branding and has at least two cores, then allow 10 users; else limit to 5 users.

Simple is also the patch. Actually, only three bytes have to be modified to cancel the limitation. (But since the code for this check is encrypted and thus hidden, the patch does a little bit more.)

The patch is the result of two phases: code analysis and design of the patch. The code analysis, or reverse engineering, reveals the relevant code block, which overrides Skype's limitation for Intel's dual-core CPUs. The patch design isolates the minimal set of instructions that need to be modified to cancel this limitation.