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EspañolSKYPE
'Skype' (IPA pronunciation: , rhymes with ''type'') is a peer-to-peer Internet telephony network founded by the entrepreneurs Niklas Zennström and Janus Friis, also founders of the file sharing application Kazaa and the peer-to-peer television application Joost. Skype allows for users to call other users from their computer and communicate via microphone, as well as call and be called from regular phones. The Skype Group, acquired by eBay in September 2005, has headquarters in Luxembourg, with offices in London, Tallinn, Prague [1] and San Jose, California.
Skype has experienced rapid growth in both popular usage and software development since launch, both of its free and its paid services. The Skype communications system is notable for its broad range of features, including instant messaging, file transfer, short message service, voice and video conferencing, its ability to use peer to peer (decentralized) technology to overcome common firewall and NAT (Network address translation) problems, its use of transparent, strong encryption and its extreme[2] countermeasures against reverse engineering of the software or protocol.
On August 16, 2007, Skype's peer-to-peer network collapsed for the first time during its four year history. It was down for almost 48 hours. It is believed that the outage was caused by millions of users simultaneously rebooting their machines following a minor Microsoft security update.[3][4]
System and Software
Technology
Main articles: Skype Protocol
The main difference between Skype and VoIP clients is that Skype operates on a peer-to-peer model, rather than the more traditional server-client model. The Skype user directory is entirely decentralized and distributed among the nodes in the network, which means the network can scale very easily to large sizes (currently about 240 million users)[5] without a complex and costly centralized infrastructure.
Skype also routes calls through other Skype peers on the network to ease the crossing of Symmetric NATs and firewalls. This, however, puts an extra burden on those who connect to the Internet without NAT, as their computers and network bandwidth may be used to route the calls of other users.
The Skype client's application programming interface (API) opens the network to software developers. The Skype API allows other programs to use the Skype network to get "white pages" information and manage calls.
The Skype code is closed source, and the protocol is not standardized. The Windows user interface was developed in Pascal using Delphi, the Linux version is written in C++ with Qt, and the Mac OS X version is written in Objective-C with Cocoa.[6]
Parts of the client use Internet Direct (Indy), an open source socket communication library.
Security
Secure communication is a feature of Skype. The encryption cannot be turned on or off. The user is not involved in the encryption process and therefore does not have to deal with the issues of public key infrastructure. Skype reportedly uses openly available, strong encryption algorithms.[7]
General
The Skype code is proprietary and closed source, and it is not planned to become open-source software, according to one of Skype's co-founders:
Que Publishing's book, ''Skype: The Definitive Guide''[8] points out:
★ Skype can utilise other users' bandwidth. (Although this is allowed for in the EULA, there is no way to tell how much bandwidth is being used in this manner). There are some 20,000 supernodes out of many millions of users logged on. Skype Guide for network administrators[1] claims that supernodes carry only control traffic up to 5 kbytes/s and relays may carry other user data traffic up to 10 kbytes/s (for one video call). A relay should not normally handle more than one "relayed connection".
★ Skype's file-transfer function does not contain any programmatic interfaces to antivirus products, although Skype claims to have tested its product against antivirus "Shield" products.
★ The lack of clarity as to content means that systems administrators cannot be sure what Skype is doing. (The combination of an invited and a reverse-engineered study taken together suggest Skype is not doing anything hostile). Skype can be easily blocked by firewalls.
★ The actual communication of any given Skype conversation uses modern encryption techniques to make conversations secure, as mentioned in the above studies.
Resource usage
A typical early version of Skype 3.0 Beta, running on a Windows XP desktop
Skype accesses the hard disk several times each minute. This can be verified by observing the HDD's activity LED, or by using a file access monitor such as FileMon.[9] With regard to internet bandwidth, certain users are selected by software to act as "supernodes". Under certain conditions, Skype is reportedly willing to accept thousands of connections, but is stated to limit itself to 40 kb/s upload and download.[10][11][12]
Confidentiality of data
Skype claims that the proprietary session establishment protocol is efficient and prevents both man-in-the-middle and replay attacks. The software is not self-certifying which means it needs to connect and login to a centralized Skype server to certify each user's public key.
Skype currently permits multiple concurrent logins: if an attacker is able to obtain a user's login password, the attacker could login as that user, and change their status to "Hidden". Thereafter, any chat sessions involving the real user are possibly copied to the hacker's "ghost" account. Provided a user keeps his/her password secure, this is not of concern.
Authenticity of user identity
Skype provides an uncontrolled registration system for users: registration requires no proof (by means of state-issued ID card) of the identity of the user. This works two ways: you can use the system safely without revealing your real-life identity to other users of the system, but on the other hand you have no guarantees that the person you communicate with is the one they say they are in real life. The downside of this is that it is easy to use the personal name (but not identity) of a trusted person as a Skype nickname and trick a naive user into revealing information or executing a program sent to them.
Major events
;2002-2005: ★ September 2002: investment from Draper Investment Company ★ April 2003: Skype.com and Skype.net domain names registered ★ August 2003: First public beta version released ★ September 2005: SkypeOut banned in South China.[13] ★ October 2005: eBay purchased Skype (Oct 14).[14] ★ December 2005: videotelephony introduced.[15] | ;2006-2007: ★ April 2006: 100 million registered users. ★ October 2006 Skype 2.0 for Mac is released, the first full release of Skype with video for Macintosh. ★ December 2006 Skype announces a new pricing structure as of January 18, 2007, with connection fees for all SkypeOut calls.[16] Skype 3.0 for Windows is released.[17] ★ March 2007 Skype 3.1 is released, adding some new features, including Skype Find and Skype Prime. Skype also released a 3.2 beta with a new feature called Send Money which allows users to send money via PayPal from one Skype user to another. ★ August 2007 Skype 3.5 released with additions such as video in mood, inclusion of video content in chat, call transfer to another person or a group, auto-redial. [18] ★ August 16/August 17, 2007 Skype users unable to connect to full Skype network in many countries.[19][20] Skype reports the system-wide crash was the result of exceptional number of logins after a Windows patch reboot ("Patch Tuesday").[21] |
Versions now exist for Microsoft Windows
Detailed changelogs
:
★ Detailed ''Windows'' changelog
:
★ Detailed ''Mac'' changelog
:
★ Detailed ''Linux'' changelog
Usage and traffic
A typical early version of Skype 1.0, running on a Windows XP desktop
| Date | Total user accounts ''in millions'' | Skype to Skype minutes ''in billions'' | Skype Out minutes ''in billions'' | Net revenue USD ''in millions'' |
|---|---|---|---|---|
| Q1 2006 | 95 | 6.9 | 0.7 | 35 |
| Q2 2006 | 113.1 | 7.1 | 0.8 | 44 |
| Q3 2006 | 135.9 | 6.6 | 1.1 | 50 |
| Q4 2006 | 171.2 | 7.6 | 1.5 | 66 |
| Q1 2007 | 195.5 | 7.7 | 1.3 | 79 |
| Q2 2007 | 219.6 | 7.1 | 1.3 | 90 |
As of June 30, 2007, Skype had a cumulative number of unique user accounts of 220 million. Users may register more than once, and as a result, may have more than one account.
It was reported that nine million concurrent Skype users were online as of January 29 2007.[24]
| Date | [25] Users online | Days |
|---|---|---|
| 2007-01-29 | 9,000,000 | 82 |
| 2006-11-08 | 8,000,000 | 71 |
| 2006-08-29 | 7,000,000 | 155 |
| 2006-03-27 | 6,000,000 | 66 |
| 2006-01-20 | 5,000,000 | 92 |
| 2005-10-20 | 4,000,000 | 155 |
| 2005-05-18 | 3,000,000 | 93 |
| 2005-02-14 | 2,000,000 | 117 |
| 2004-10-20 | 1,000,000 | 418 |
| 2003-08-29 | 0 | - |
Although the volume of international traffic routed via Skype is significant, the quantity is still small when compared to the cumulated global switched and VoIP traffic. Computer-to-computer traffic between Skype users in 2005 was equivalent to 2.9% of international carrier traffic in 2005 and approximately 4.4% of total international traffic base of 264 billion minutes in 2006.[26]
Skype incorporates some features which obfuscate its traffic, but it is not specifically designed to thwart traffic analysis and therefore does not provide anonymous communication. Some researchers have also been able to watermark the traffic so that it is identifiable even after passing it through an anonymizing network [2].
===Supported audio codecs[27]===
★ SVOPC
★ AMR-WB
★ G.729
★ G.711
★ iSAC
★ iLBC
Features
Main articles: Features of Skype
SkypeOut
SkypeOut rates as of May 2006, in USD$ per minute
''SkypeOut'' allows Skype users to call traditional telephone numbers, including mobile telephones, for a fee. This fee is as low as US$0.024 per minute for most developed countries, and as high as US$2.142 per minute for calls to the dependency of Diego Garcia. Beginning January 2007, Skype also charges an equivalent of €0.039 for each SkypeOut call, in addition to the ordinary rate.[28] After 180 days of not making a SkypeOut call the Skype balance expires.
As of January, 30th 2007, SkypeOut calls to Canada and the United States are no longer free.
SkypeOut calls to most toll free numbers in France (+33 800, +33 805, +33 809) , Poland: (+48 800) , UK: (+44 500, +44 800, +44 808) and the United States and Canada: (+1 800, +1 866, +1 877, +1 888 ) are free for all Skype users, even if they do not have the SkypeOut service. [3][4] . However, for many other countries SkypeOut doesn't support calling toll-free and premium rate numbers, and SkypeOut doesn't support calling emergency numbers (such as 112 in Europe or 911 in the U.S.A.).
Quality of service is not guaranteed. Dropouts, broken connections and compression distortion are frequently observed by users.
Skype 1.4, running on a Linux desktop, over 7,630,000 people online
SkypeIn
''SkypeIn'' allows Skype users to receive calls on their computers dialed by regular phone subscribers to a local Skype phone number. It permits users to subscribe to numbers in Australia, Brazil, Chile[29]
, Denmark, the Dominican Republic, Estonia, Finland, France, Germany, Hong Kong, Japan, Poland, New Zealand,29 Sweden, Switzerland, UK, Romania and the United States.
For example, a user in San Francisco could create a local telephone number in Helsinki. Callers from Helsinki would pay only local rates to call that number.
Criticisms
Skype has been criticized over its use of a proprietary protocol, instead of an open standard like H.323 or SIP, since this makes it much more difficult, if not impossible, for other developers to interact with Skype. Some have theorized that the decision was made to prevent competition over business with SkypeOut.
Due to the design of the protocol, if given access to an unrestricted network connection, Skype clients can become supernodes. These supernodes hold together the peer-to-peer network and provide data routing for other clients behind more restrictive firewalls, which can generate a significant amount of bandwidth usage. For this reason, some network providers, such as universities, have banned the use of Skype.[30]
A third party paper analyzing the security and methodology of Skype was presented at Black Hat Europe 2006.[31] It analyzed Skype and made these observations:
★ Heavy use of anti debugging techniques (used to deter development of alternative clients, hacking tools)
★ Significant use of obfuscated code (slows reverse engineering, less description of what program code does internal to the executable file)
★ Keeps chatting on the network, even when idle (even for non-supernodes. May be used for NAT traversal)
★ Blind trust in anything else speaking Skype
★ Ability to build a parallel Skype network
★ Lack of privacy (Skype has the keys to decrypt sessions)
★ Heap overflow in Skype
★ Skype makes it hard to enforce a (corporate) security policy
★ "No way to know if there is/will be a backdoor"
SkypeOut rates are "per minute" based, contrary to the trend in charges for calls from conventional telephones. In some countries, many calls are charged at a specified fixed amount per call. In this method, SkypeOut is more expensive for longer calls, whereas it is cheaper for relatively short calls.
Furthermore, there has been a surge of complaints about Skype's poor customer support [32].
As of June 2007, Skype still does not provide a direct way of contacting its customer support, relying solely on its web portal for all related issues. In particular, customers who paid for services such as SkypeOut, have repeatedly expressed their frustration with Skype's lack of response, claiming that it had been disregarding or not providing an adequate response to their complaints about significant issues, such as incorrect billing. Some customers have complained about Skype's
unclear charges to their account. In some cases, when those charges were eventually explained to them, they could be categorized as hidden fees.
When Skype 2.0 was released, AMD filed a lawsuit claiming the software only offers 10-way conference calls on dual core Intel processors, while other chips, including all AMD chips, will only offer 5-way conference calls.[33]
Another criticism of Skype has been content filtering. See: Internet censorship in the People's Republic of China.
While available for Windows, Mac OS X and Linux (i386 platform) operating systems, there is no Skype version for the Palm OS, used in mobile devices like the Treo 700p smartphone nor for the PowerPC version of Linux.
Skype has been criticized in the Linux community for bugs and delays in the Linux version [5]. The Mac OS X version also lacks some of the advanced features included in Skype for Windows.
There have also been criticisms of Skype blocking and disabling customer accounts from using the SkypeOut service [6].
Also, when using SkypeOut to call toll-free numbers, users may experience call degradation when using the keypad to enter numerals into automated systems.
Skype was also found to access BIOS data[34] to identify individual computers and provide DRM protection for plug-ins.[35][36]
Skype 1.4.0.99 has also been found to read the /etc/passwd and Firefox profile on Linux machines[37].
Legal and political aspects
Skype faces challenges from two main legal and political directions: challenges to its intellectual property and political concerns by governments wishing to control the telecommunications systems of the respective countries.
Skype's technology is proprietary and closed to outside review. It is unknown to what extent it can potentially intrude upon other parties' patents and copyrights. It is not unreasonable, therefore, to expect legal challenges from third parties concerning Intellectual Property issues.
Skype also supply Skype-in phonelines without requiring proof of address, which is illegal in some countries.
Legal challenges
Streamcast lawsuit
In January, 2006, StreamCast Networks filed a complaint in U.S. District Court in Los Angeles, accusing Skype of stealing its peer-to-peer technology. The $4.1 billion lawsuit did not initially name eBay, Skype's parent company; however, the lawsuit was amended in a filing with Federal Court in the Central District of California on May 22, 2006, to include eBay and 21 other parties as defendants.
Streamcast seeks a worldwide injunction on the sale and marketing of eBay's Skype Internet voice communication products, as well as billions of dollars in unspecified damages.
IDT lawsuit
On June 1, 2006, Net2Phone (the Internet telephone unit of IDT Corp.) filed a lawsuit against eBay and Skype accusing the unit of infringing , which was granted in 2000.[38]
Political issues
China 2005
For a brief period, SkypeOut was blocked in some regions of mainland China (notably Shenzhen) by the operator China Telecom for undisclosed reasons; it has been speculated that this may relate to SkypeOut's ability to take lucrative international and long-distance business away from the People's Republic of China's state-controlled telecommunications companies.
Skype is one of many companies (others include AOL, Google, Microsoft, Yahoo, Cisco) which have cooperated with the Chinese government in implementing a system of Internet censorship in mainland China. Critics of such policies argue that it is wrong for companies to assist in such policies, which might allow them to profit from censorship and restrictions on freedom of the press and freedom of speech. Human rights advocates such as Human Rights Watch and media groups such as Reporters Without Borders state that in their view, if companies stopped contributing to the authorities' censorship efforts the government could be forced to change.[39]
Niklas Zennström, chief executive to Skype, told reporters that its joint venture partner in China is operating in compliance with domestic law. "Tom Online had implemented a text filter, which is what everyone else in that market is doing," said Mr Zennström. "Those are the regulations," he said. "I may like or not like the laws and regulations to operate businesses in the UK or Germany or the US, but if I do business there I choose to comply with those laws and regulations. I can try to lobby to change them, but I need to comply with them. China in that way is not different."[40]
France 2005
In September 2005, the French Ministry of Research, acting on advice from the General Secretariat of National Defence, issued an official disapproval of the use of Skype in public research and higher education; some services are interpreting this decision as an outright ban. The exact reasons for the decision were not given.
United States, CALEA 2006
In May 2006, the FCC successfully applied the Communications Assistance for Law Enforcement Act to allow wiretapping on digital phone networks. Skype is not yet compliant to the Act, and has so far stated that it does not plan to comply.[41]
India 2006
In December 2006, the Indian government announced it is preparing a crackdown on Internet telephony services, citing security risks and loss of revenue. The clampdown is targeted at outsourcers and other Indian IT businesses that use foreign-owned Internet telephony services, such as Skype and Yahoo!, to cut their phone bills and evade the six percent revenue share and 12 percent tax imposed on local services by the government. According to The Times of India, companies must reveal the names of licensed service providers they purchase bandwidth and Internet telephony minutes from. Companies will also have to undertake that they will not use the services of unlicensed Internet service providers.
United Arab Emirates 2006
Skype was abruptly blocked in the UAE for undisclosed reasons—Skype users in the United Arab Emirates are being blocked from the Skype.com site, which prevents them from buying minutes for use with SkypeOut and taking advantage of deeply discounted international calling rates. The blockage has been speculated to originate within Etisalat, the only ISP in the UAE.
Oman
The Sultanate of Oman has also blocked access to the Skype.com website preventing users from accessing Skypeout in order to maintain Omantel's monopoly on the telecommunications market in the country. This has also to do with security issues as well as economic ones as it is difficult to monitor the calls made with Skype. Many other Persian Gulf countries pursue similar policies regarding Skype for largely the same reasons.
Skype group (corporate)
Main articles: Skype Limited
On October 14 2005, eBay acquired the company for €1.9 billion in cash and stock, plus an additional €1.5 billion in rewards (earn out) if goals are met by 2008.[42][43]
See also
★ Skype Protocol
★ Presence information
★ Voice over IP
★
★ Comparison of VoIP software
★ Instant messaging
★
★ Comparison of instant messaging clients
★
★ Comparison of instant messaging protocols
★ Videoconferencing
★ Secure communication
★ Skype Journal: An independent online magazine about Skype
★ Nuvvo eLearning Service: an on-demand service with SkypeWeb Presence integration
★ Unyte Desktop Sharing: Skype integrated desktop/application sharing solution
★ Festoon Inc.: Provider of a plugin and codec that allows multi-party video conferencing to Skype
★ Yahoo! Voice
★ Windows Live Call
★ AIM Phoneline
Alternatives
Gizmo Project
SightSpeed
References
1. Skype is expanding engineering to Prague Jaanus Kase
2. Silver Needle in the Skype
3. Skype blames outage on user reboot The Times, August 20, 2007.
4. What happened on August 16 Skype official blog, August 20, 2007.
5. 1 million Joost users prepare for year-end launch
6. Interview with Jaanus Kase from Skype
7. Skype Privacy FAQ
8. Skype: The Definitive Guide Harry Max
9. FileMon for Windows
10. Swiss magazine digs deeper in social blog Bruno Giussani
11. Fear of a Skype Planet
12. Skype supernodes sap bandwidth
13. China bans Skype Jack McCarthy
14. eBay Completes Acquisition of Skype
15. Skype Launches Next Generation Free Internet and Video Calling for Everyone
16. Skype to Announce Disruptive Pricing Strategy for SkypeOut Retrieved: December 19, 2006
17. What is Skype?
18. Skype Takes Video One Step Further
19. http://www.chron.com/disp/story.mpl/ap/fn/5059323.html
20. Error in Skype’s Software Shuts Down Phone Service
21. Skype blames outage on user reboot
22. Skype VoIP User Guide, FAQ, Hints and Resources How to run Skype from a USB stick
23. Skype for Symbian Coming
24. Nine million online Jaanus
25. 8 million onliners
26. International carriers' traffic grows despite Skype popularity
27. Is Skype's own codec good? - Skype Forums
28. Connection Fee for SkypeOut Calls
29. Four new SkypeIn countries Villu Arak
30. More universities banning Skype Ryan Paul
31. Silver Needle in the Skype Philippe BIONDI and Fabrice DESCLAUX
32. Skype callers: 'Customer service, please?' Ben Charny
33. AMD's lawyers call on Skype Tom Krazit
34. pagetable.com » Blog Archive » Skype Reads Your BIOS and Motherboard Serial Number
35. Skype Security Blog - Skype Extras plug-in manager
36. The Register » Skype snoop agent reads mobo serial numbers
37. Skype Forums » English » Platforms, community support » Skype for Linux » Skype 1.4.0.99 reads /etc/ passwd and firefox profile!
38. Skype Under Attack
39. Skype uses peer-pressure defense to explain China text censorship
40. Skype says texts are censored by China
41. Can Skype Keep Its Secrets?
42. eBay Completes Acquisition of Skype
43. eBay to buy Skype in .6bn deal
External links
★ Official Skype website
★ Scientific Research on Skype (Reverse Engineering, etc.)
★ White paper on Skype, focus on supernodes
★ Skype Security Evaluation by Tom Berson (Anagram Laboratories)
★ Skype security, obfuscation and protection against reverse-engineering techniques analyzed at Black Hat conference 2006
★ Skype VoIP User Guide, FAQ, Hints and Resources Includes some hard-to-find info for users
★ How to install Skype screencast (Windows XP)
Skype Phones
★ Simplyphone Skype hardware partner developing Skype Certified plug-in and wireless phones
★ RTX Skype partner developing USB and embedded cordless Skype phones
★ Edge-Core WM4201 Wi-Fi Phone WiFi Skype phone
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