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Skype Network Administrator’s Guide Skype 3.0 Beta 27

2006-10-31 Document version 2.0 Beta

Is Call Forwarding to a PSTN less secure? Yes and no.

In the Skype network, all voice calls, chat messages, video calls, and file transfers are

encrypted end-to-end to ensure privacy. However, at the point a Skype voice call leaves the

Skype network, the call is decrypted:

• When a Skype voice call leaves the Skype network and enters a traditional telephony

network through a termination provider, the call is decrypted and sent over the PSTN the

way that any voice call may be transmitted over the PSTN. As a result, the call becomes

susceptible to advanced techniques used by law enforcement and others to “tap the line”.

• Similarly, when a Skype call leaves the Skype network and enters a call center through a

SIP (Session Initiation Protocol) gateway, the Skype call is no longer under Skype's

control and is unencrypted at that point forward.

Therefore, given a scenario whereby a customer or account holder uses Skype to contact

the company, and whereby the call is forwarded to a PSTN number that terminates at the

company’s call center switch, you can consider calls that originate on Skype to have the

same operational level of security and privacy as calls that originate and terminate over the

PSTN or call center.

There is one caveat, however. As mentioned above, IT administrators must consider that

Skype runs on mass-market operating systems. This means that Skype can only provide an

operational level of security or privacy afforded to Skype users in the context of the

security provided by the operating systems on which the Skype client runs.

Given this, even though Skype network traffic cannot be intercepted and decoded while in

transit, audio files for voicemail messages and text files associated with chat histories may

be vulnerable on end user computers and file systems, depending on the level of security

present on the user’s network and computer.

Are Skype Users at Risk of Trojan Viruses and Other Threats?

For obvious reasons, malicious code such as Trojan viruses, malware, adware, and spyware

remain high on the list of concerns for IT management and security personnel. The

question about whether end users are susceptible to such threats must be addressed in two

separate ways.

Can a Hacker Send a Trojan Virus via Skype to an IVR? No.

Skype’s capability to enable end users to send and receive files (which may include

potentially malicious code) utilizes Skype's File Transfer feature, which lets a Skype user

send a file to one or more other Skype users.

Such files cannot be transmitted surreptitiously via Skype’s pseudo-isochronous voice or

video stream so there is no risk of a hacker transmitting a Trojan virus (or other file) to

either the company’s IVR or the Skype user’s computer.

Refer to “Enterprise-Wide Installation and Setting Policies” for information on how to

disable this feature using a Group Policy Object or Registry Key.

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Skype - 3.0 beta Betriebsanweisung Seite 27