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Page 19 IT Administrators Guide

3.0 Security and privacy

We’re committed to secure communications and protecting our users’ privacy. We follow

the latest best practice in security, including:

Encryption of data end-to-end with 256-bit AES encryption keys.

Protection of encryption keys which aren’t revealed to users or escrowed to third

parties and are discarded when the session ends.

Use of credential-based identities and end-to-end encryption to make 'man-in-

the-middle' attacks very unlikely.

Our security model also prevents anyone with a supernode or relay node from interfering

with, or capturing any part of, a Skype communication, even if they can collect or sniff

network data packets. It also makes it very difcult for anybody to eavesdrop on content

by installing an internet computer in the theoretical path of Skype trafc.

3.1 Transport-level security

No one can guarantee complete anonymity or secrecy. However, our transport layer

encryption uses the Advanced Encryption Standard (AES) algorithm. This makes it very

unlikely that your Skype communications will be intercepted or decrypted over the P2P

network.

We use both public and private keys to secure all signals over the P2P network, as well

as communications content. Our cryptographic model uses public-key and symmetric-

key cryptography, including the AES algorithm in 256-bit integer counter-mode. We also

use the 1024-bit RSA algorithm to negotiate symmetric AES keys. User’s public keys are

certied at login using 1536 or 2048-bit RSA certicates.

3.2 Security limitations

Skype encryption and control mechanisms are only able to protect communications

when all users in the communication are utilizing the unmodified, Skype-produced

software over the public internet. When communications transit other third party systems,

including modified software, servers, and phone networks, the user may experience

decreased privacy and security levels. An example is a call to a landline or mobile phone,

which is carried immediately prior to termination on the regular telephony networks

(PSTN or mobile). As a result, this call is only as secure as any regular telephone or

mobile phone call carried on that network. Calls to your Online Number, if you have one,

exhibit similarly reduced levels of security. Another example is a call made from the

Skype For Your Mobile (SFYM or Skype Lite) application, which uses regular (2G) mobile

networks to carry the voice part of any communication. These calls are similarly only as

secure as the underlying mobile network and regular mobile calls carried on them.

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Skype - 2.0 Guía de usuario Pagina 19