Skype

Skype is a Logiciel owner and service owner of voice on IP (VoIP) developed by the creators of Kazaa and The Venice Project (renamed Joost), Niklas Zennström and Janus Friis.

Functionalities

It makes it possible to telephone free only between two computers or terminals equipped with Skype and connected to Internet, thanks to a Microphone and Haut-parleur S, or a Microphone-helmet or Téléphone connected on the computer (for example by port USB). It is also equipped with a basic instant messaging making it possible to the users to textually communicate and to be transmitted files.

Skype also makes it possible to carry out paying calls towards fixed and mobile phone lines and recently proposes to receive phone calls since fixed telephones and mobiles, but this only in certain countries.

Since January 2006 and the release of version 2.0 of Skype for Windows, its users can also communicate by Visioconférence. This service is proposed in beta release according to the terms of the editor himself, but functions without known important dysfunctions.

Skype became one of the communications tools vocal on computer most used as well as Window Live Messenger, although posing problems of interworking (reciprocal exclusiveness in the protocol and software), in addition to the preoccupations with a confidentiality (Sécurité by the darkness, intrinsically unverifiable).

Principle of operation

Skype employs a technology P2P VoIP, mixture of Peer-to-peer (station-with-station) and of VoIP (Voix on network IP), to connect itself with the other users of Skype, allowing occasion consequently a resource sharing: the users having a broadband connection discharge those having the low flow from part of the traffic which would be likely to block their connection; they also allow the interconnection between the users being behind a Pare-feu. An outgoing access TCP towards all the wearing of destination above 1024 or towards port 80 is necessary. To obtain best vocal quality it is preferable to open the port given in the options of Skype. However, the encrypted and opaque traffic being, it is difficult to know the contents of information forwarding without authorization on the computer of a user of Skype (nobody knew to determine it to date), posing obvious problems of confidentiality.

This software functions under Microsoft Windows, but also on the systems GNU/Linux (on X86), Mac OS X and Pocket PC. It uses the protocol S TCP and UDP and makes it possible to make conference S vocal to hundred people.

The user interface Windows was developed in Pascal Object with Delphi Win32, the version Linux in C++ with Qt and that of Mac OS X in Objective-C with Cocoa.

Skype created a controversy by using a protocol closed owner and not-standard, because that goes against the Interopérabilité, which is at the origin of the success of the Internet, while functioning on open standards of communications making it possible all to communicate by using different but compatible software implementations.

Technology P2P VoIP having proven reliable technically and commercially, the organization IETF established a standard (in English) on this subject: Session Initiation Protocol (shortened in SIP).

Safety

Skype is at the origin of a debate on the safety of the communications by the technology of the Voix on IP and safety related to the software Skype itself. The major questions come from what Skype uses certain users to relay the communications of other users and who Skype is a completely closed application using of the protocols closed to make safe its traffic.

Safety of the communications

  • All the traffic of data of Skype is encrypted (quantified).

  • Skype claims to use algorithms of Cryptographie known and difficult to break.

  • the user does not have access to the parameters of coding and, consequently, technical decisions concerning a Infrastructure with public keys does not have to make.

One of the objectives of coding is of raising the questions of confidentiality for the communications which are relayed by other users. These choices had an impact on the market of the Voix on IP, in general. The Chiffrement of the communications is a stake which gained interest near the users.

Trojan horse

Skype would have been the subject of an official statement of the Minister of education main road French during the month of September 2005, requiring its desinstallation of the stations equipped in all the public schools. It would seem that certain Skype waiters make it possible to intercept information and the software could also be used as shelter with a Trojan horse.

This information is to be taken with tweezers, since actually, it is a Trojan horse being propagated by e-mail which is made pass for an update of Skype. This alarm of safety dated October 18th, 2005. The danger thus comes from a counterfeit and not from Skype itself.

To protect itself from these problems will be difficult for this administration : to regulate the problem seems more complex than a simple parameter setting of fire wall. One can read on this subject an article of ZDNet.fr which seems to confirm that this malware is transmitted only by email, as well as the official reaction of Skype on this subject, which points out the bases of the distribution of software of the large companies, namely that the programs and the patchs are never distributed by email.

  • See an article of 01net, which recalls that it is not only the business of the Trojan horse which started this wave of desinstallation, but also the fact that Skype is a gigantic block box in which nobody can be assured knowing exactly what occurs.

  • NB: The newspaper Pirat Mag (N° 20 p. 4) indicates that which revealed this business initially is Guillaume Champeau de Ratiatum.

Integrity of the Skype software

The Source code of Skype not being public, no expert can evaluate it in an independent way. Nevertheless Philippe Biondi and Fabrice Desclaux of EADS practiced a study of Retro-engineering " Silver Needle in the Skype". They presented it at the time of the conference Black Hat Europe in March 2006 and with SSTIC in June 2006.

  • Skype is perfect a " box noire". It is extremely difficult to analyze what Skype does and which is the method used. Skype uses the Sécurité by the darkness and makes voluntarily difficult the analysis of the traffic by Retro-engineering.

  • the software uses many impenetrable Code and Somme of control to prevent the retro-engineering of the source code.

  • Any computer on which Skype is installed, which has a rather fast processor, a connection to high-flow, and is not behind a Routeur NAT or a Pare-feu becomes a " relais" for the other users; a super-node in terminology Peer to peer. Skype can thus use the connection of a user to relay the traffic of the others. This use is mentioned in Article 4 of the License agreement end user.

  • the agility of the software to circumvent the avoid-fires and the Routeur S NAT explains its success near the private individuals. This quality makes more difficult the task of the administrators networks who wish to block the Skype traffic.

  • Although Skype does not provide application program interfaces to the software designers antivirus, it would seem that the majority of the antivirus products block the transfer of file infected. Skype however recommends to the users to manually test the files sent and receipts. This information is contradicted by the " Skype Guides for Network Administrators" who explains by which mechanism the antivirus software can intercept the tranférés files.

Free and standard alternatives

Protocols open standards

Software

External bonds

  • Official site

References

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