Skype - 3.0 beta Guide de l'utilisateur télécharger pdf (Page 26)

Skype Network Administrator’s Guide Skype 3.0 Beta 26

2006-10-31 Document version 2.0 Beta

Although the name “hole punching” might suggest otherwise, this technique does not

compromise the security of private networks but instead seeks to establish communications

by working within the policy framework of most NATs. These techniques signal to the

NAT devices in the path of a communication that the P2P sessions have been solicited and

should therefore be passed.

How Secure is the Skype telephony connection?

Can anybody listen in on customer phone calls? No.

Skype's security is integrally linked to its architecture. All voice calls, chat messages, video

calls, and file transfers are encrypted end-to-end (in the Skype network) to ensure privacy.

Even though Skype does not guarantee complete anonymity or secrecy, it does provide

industry-leading transport layer security to ensure that message content traveling over the

Skype network on the Internet cannot be tapped or intercepted.

To accomplish this, Skype relies on a system of public and private keys to keep the

contents of communication confidential. This includes all signals used to control the Skype

network as well as communications content such as voice, video, text, and data. The use of

encryption means it is not possible to know what information is traveling in the Skype

network among integral parts, including nodes, supernodes or relay hosts.

Skype’s network traffic cannot be intercepted and decoded while in transit. The

cryptographic model behind Skype employs both public key and symmetric key

cryptography, including the AES algorithm, used in 256-bit integer counter mode. Skype

also uses 1024-bit RSA to negotiate symmetric AES keys. User public keys are certified by

the Skype server at login using 1536 or 2048-bit RSA certificates.

All communications between any pair of Skye users is sent simultaneously over a single

session, using a technique called multiplexing. The contents of voice calls, text chats and

any other form of Skype communication is sent with an equal degree of security.

However, while Skype does offer a private communication channel, network

administrators must keep in mind that Skype runs on mass-market operating systems. This

means that Skype provides an operational level of security or privacy for Skype users in

the context of the security provided by Microsoft Windows, Mac OS X, Pocket PC, Linux,

and the other operating systems on which the Skype application runs.

Therefore, Skype does not provide a secure communication platform in the strictest sense,

and it is not a secure file storage solution either. As a result, Skype-related data,

transmissions, and files are only as secure as the data on the computing devices running the

Skype client.

In other words, while Skype network traffic cannot be intercepted and decoded in transit,

once it is decrypted the streaming audio/video, and audio/video/text files may be

vulnerable to malicious attacks, depending on the level of security that the user has in

effect.

Once a text message, file transfer, or audio/video stream is received by the intended

receiver, the Skype client cannot prevent the copying, archiving or redistribution of the

received message.

The bottom line is this. The Skype client protects the confidentiality communications while

in transit, whether the connection is made directly between Skype clients or is relayed

through a third party.

It remains the responsibility of users themselves to protect their communications prior to

sending and, similarly, following receipt, just as they would with e-mail, and email

attachments.

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Skype - 3.0 beta Guide de l'utilisateur Page 26

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