Online Psychology Degree A First Step to a Career as a Military Psychologist 2019

Becoming a psychologist, no matter what the specialty, requires advanced education, often with either a graduate degree in general psychology or a doctorate degree in general psychology, along with at least two years of full-time study and internship experience. Many students are now deciding to compete for military training opportunities and enter a career as a military psychologist. Along with top-notch education, military interns and fellows get the opportunity to experience military life and to serve the country. Internship Opportunities for Psychology Students Successful students in military internships come from a variety of psychology graduate schools. Navy, Army, and Air Force interns receive training in military life and administration. They also gain exposure to specialty areas within psychology, including health and sport psychology and pediatrics. Military internships emphasize a multidisciplinary approach to patient care, allowing interns to interact with psychiatrists, other physicians, and other members of the healthcare team. Students from psychology graduate schools may apply to two Navy locations in Bethesda, MD or San Diego; three Air Force locations in Maryland, San Antonio, and Dayton, OH; and three Army locations in Honolulu, Washington, DC, or Augusta, GA. .u87fe3179de95fdbf9220f6f9c70a7be1 { padding:0px; margin: 0; padding-top:1em!important; padding-bottom:1em!important; width:100%; display: block; font-weight:bold; background-color:#eaeaea; border:0!important; border-left:4px solid #34495E!important; box-shadow: 0 1px 2px rgba(0, 0, 0, 0.17); -moz-box-shadow: 0 1px 2px rgba(0, 0, 0, 0.17); -o-box-shadow: 0 1px 2px rgba(0, 0, 0, 0.17); -webkit-box-shadow: 0 1px 2px rgba(0, 0, 0, 0.17); text-decoration:none; } .u87fe3179de95fdbf9220f6f9c70a7be1:active, .u87fe3179de95fdbf9220f6f9c70a7be1:hover { opacity: 1; transition: opacity 250ms; webkit-transition: opacity 250ms; text-decoration:none; } .u87fe3179de95fdbf9220f6f9c70a7be1 { transition: background-color 250ms; webkit-transition: background-color 250ms; opacity: 1; transition: opacity 250ms; webkit-transition: opacity 250ms; } .u87fe3179de95fdbf9220f6f9c70a7be1 .ctaText { font-weight:bold; color:inherit; text-decoration:none; font-size: 16px; } .u87fe3179de95fdbf9220f6f9c70a7be1 .post Title { color:#000000; text-decoration: underline!important; font-size: 16px; } .u87fe3179de95fdbf9220f6f9c70a7be1:hover .postTitle { text-decoration: underline!important; } READ Associate of Applied Business Evening and Weekend Business DegreesFellowship Opportunities for Psychology Students In addition to internships, the military also offers fellowships for doctorate students. Programs exist in a variety of subjects, such as neuropsychology, childrens mental health, developmental disabilities, and even a new program with a post-9/11 emphasis. Fellowships take place at prestigious universities, such as Yale and Harvard and, like the internships, involve competition among some of the nations best psychology graduate degree students More Information on Military Education and Careers for Psychologists The Society for Military Psychology, Division 19 of the American Psychological Association, is the professional organization of military psychologists. Its membership is made of military psychologists along with researchers and educators. Students looking for information on a career, or for training opportunities with the military, may join a special mentor network for free advice from professionals already in the field. Job Outlook for Psychologists Psychologists in general are expected to see job growth of 18 to 26% through the year 2018. Employment is expected to grow faster than average due to increased awareness of mental health issues and more willingness by the public to seek out help. However, psychologists with only a bachelors degree in psychology are expected to have difficulties finding relevant positions within psychology. A graduate degree in general psychology or a doctorate degree in general psychology is strongly recommended according to the Bureau of Labor Statistics. .u38c59a81a9222c0306024f0ad4ec9800 { padding:0px; margin: 0; padding-top:1em!important; padding-bottom:1em!important; width:100%; display: block; font-weight:bold; background-color:#eaeaea; border:0!important; border-left:4px solid #34495E!important; box-shadow: 0 1px 2px rgba(0, 0, 0, 0.17); -moz-box-shadow: 0 1px 2px rgba(0, 0, 0, 0.17); -o-box-shadow: 0 1px 2px rgba(0, 0, 0, 0.17); -webkit-box-shadow: 0 1px 2px rgba(0, 0, 0, 0.17); text-decoration:none; } .u38c59a81a9222c0306024f0ad4ec9800:active, .u38c59a81a9222c0306024f0ad4ec9800:hover { opacity: 1; transition: opacity 250ms; webkit-transition: opacity 250ms; text-decoration:none; } .u38c59a81a9222c0306024f0ad4ec9800 { transition: background-color 250ms; webkit-transition: background-color 250ms; opacity: 1; transition: opacity 250ms; webkit-transition: opacity 250ms; } .u38c59a81a9222c0306024f0ad4ec9800 .ctaText { font-weight:bold; color:inherit; text-decoration:none; font-size: 16px; } .u38c59a81a9222c0306024f0ad4ec9800 .post Title { color:#000000; text-decoration: underline!important; font-size: 16px; } .u38c59a81a9222c0306024f0ad4ec9800:hover .postTitle { text-decoration: underline!important; } READ Find Online Science and Engineering Degree ProgramsIn order to become a military psychologist, advanced education is essential. Online psychology graduate schools, such as Capella University, offer several Master of Science in Psychology programs as well as PhD in Psychology programs. Students may search for additional programs through College-Pages.com, an education resource website with an extensive list of available programs and education information. Related ArticlesGeneral Engineering Degree The Profession of Engineering Attracts Clever, Practical DesignersColleges and Universities in Guam Pursuing Online Education in GuamMaster of Science in Counseling Psychology Current Job Forecast for Professionals with a Master of Science in Counseling PsychologyNevada Colleges and Universities Pursuing Online and Campus Based Education in Nevada, the Silver StateTop Internship Mistakes to AvoidDelaware Colleges and Universities Pursuing Online and Campus-based Education

The World War II And Nazi Concentration Camps - 1935 Words

Introduction The First World War (1914-18) created the instability in Europe which set the stage for another international conflict, World War II. It broke out two decades later and would prove even more devastating. Rising to power in an economically and politically unstable Germany, Adolf Hitler and his National Socialist (Nazi Party) rearmed the nation and signed strategic treaties with Italy and Japan to further his ambitions of world domination. Hitler’s invasion of Poland in September 1939 drove Great Britain and France to declare war on Germany, and World War II had begun. Over the next six years, the conflict would take more lives and destroy more land and property around the globe than any previous war. Among the estimated 45-60†¦show more content†¦Nazi’s authority had dramatically increased through its control over the police since Hitler used a suspicious fire in the German parliament in February 1933 to suspend basic civil rights. Political opponents, along wit h Jews, were subject to intimidation, persecution, and discriminatory legislation. Using the Civil Service Law of April 1933, German authorities began eliminating Jews from governmental agencies, and state positions in the economy, law and cultural life. The Nazi government abolished trade unions. By mid-July, the Nazi party was the only political party left in Germany. Hitler had the final say that, Nazi foreign policy was guided by the racist belief that Germany was biologically destined to expand eastward by military force and that an enlarged, racially superior German population should establish permanent rule in eastern Europe and the Soviet Union. Within this framework, â€Å"racially inferior† peoples, such as Jews and Gypsies, would be eliminated from the region. However, anti-Semitism in Europe did not begin with Adolf Hitler. Though use of the term itself dates only to the 1870s, there is evidence of hostility toward Jews long before the Holocaust—even as far back as the ancient world, when Roman authorities destroyed the Jewish temple in Jerusalem and forced Jews to leave Palestine. The enlightenment, during the 17th and 18th centuries, emphasized religious toleration, and in the 19th century Napoleon and otherShow MoreRelated HOLOCAUST Essay1275 Words   |  6 Pages As tensions mounted up until the point of World War II and the war stormed through Europe, another battle silently raged. Not only did Hitler and the Nazi party wage war on countries throughout Europe, they also assaulted and purged entire innocent groups. The Holocaust began in 1933 and reached its height in WW II, while coming to an end with the war in 1945. Hitler used the Holocaust as a mechanism to rid his racially superior German state ofRead MoreThe Role that Other Lesser-known Concentration Camps Play in the Holocaust1377 Words   |  6 PagesAs World War II continued on to in the spring of 1945, the prisoners in the Buchenwald concentration camp in Germany were worn down, starved of food, and weary. See, not many people know about the other concentration camps that took place during the Holocaust. Though Auschwitz and Dachau are the most commonly known concentration camps, the lesser-known concentration camps also played an important role in the Holocaust - such as holding prisoners of war due to their strategic geographic positionsRead MoreThe Holocaust Memorial Center : Family Campus1466 Words   |  6 PagesHolocaust Memorial Center Zekelman Family Campus is about the horrendous events such as hate crimes that were happening during World War II. The definition of Holocaust from the museum website perspective is â€Å"The Holocaust was the systematic, bureaucratic, state-sponsored persecution and murder of approximately six million Jews and five million other persons by the Nazi regime and its collaborators† (Holocaust and Survivor Defined.). â€Å"The term Holocaust comes from the Greek words of â€Å"holos† (whole)Read MoreThe Ss And The Nazi World War II1117 Words   |  5 PagesThe SS, or Schutzstaffel, played a variety of roles before and during World War II, showing their loyalty to Hitler and patriotism. From their beginning as personal bodyguards of about eight men, to being an elite organizatio n with police units and special forces, these â€Å"men in black† used their power to become the most powerful men in Germany. The SS proceeded with mass killings and watched over concentration camps. They did Hitler’s â€Å"dirty work.† In 1929, Heinrich Himmler took control of the SSRead MoreThe Holocaust : The World s Perspective Essay1455 Words   |  6 Pagesdefeated the Nazis. The Nazis used the term the Final Solution to state to their plan to murder the Jewish people and people they called the â€Å"others†. Holocaust, originated from the Greek word holokauston and means sacrifice by fire, this refers to the Nazi s persecution and planned genocide of the Jewish people and many others. The Nazi’s targeted Jewish people, Gypsies, Homosexuals, Jehovah s Witnesses, twins and the disabled for torture and persecution, anyone who fought back the Nazis was sentRead MoreThe Rise Of The Second World War1124 Words   |  5 PagesEurope, the war are closely related to the rise of other wars, especially in Germany. The increasing of the Second World War is viewed as being closely related back to the First World War. In that war Germany under the right-wing of Kaiser Wilhelm II along with his associates, had been beat by countries like: The United Kingdom, United States, France, Russia and others. The war was directly related by the winners on the nationalism of Germany, even tho it was Germany that started the war with an attackRead MoreThe Holocaust : 86 Years Later1534 Words   |  7 Pagesthe tragic campaign waged by the Nazis during World War II, and their â€Å"systematic, state-sponsored persecution and murder† of six million Jews and others who didn’t fit the specific vision or â€Å"perfect race.† Adolf Hitler, the known anti-Semitic Nazi leader, viewed the Jews as an inferior race and threat to what he viewed as racial purity. Under the guise of the war, Hitler’s solution revolved around mass killing centers constructed within the concentration camps of occupied Poland. One man’s orchestratedRead MoreThe Nazi Party and The Holocaust1119 Words   |  4 PagesJanuary 30th, 1933. Soon after, Hitler gained a numerous amount of followers and rapidly developed his Nazi Germany. Led by visions of racial purity and spatial expansion, the Nazis mainly targeted Jews. In addition, Nazis also targeted Gypsies, homosexuals, Jehovahs Witnesses and disabled people along with anyone who resisted them. This tragic event lasted a total of 12 years. On April 1, 1933, the Nazis announced a boycott of all Jewish businesses. This was the first of many actions taken to slowlyRead MoreAdolf Hitler Essay827 Words   |  4 PagesAdolf Hitler was one of the most feared and cruel men in world history, but how did he come to power? Hitler was one out of a few men to be feared by thousands of people. Hilter was responsible for killing millions of innocent people, mostly of the Jewish religion. He was the chancellor of Germany for 12 years and the leader of the Nazi party. He was a very important person in history, most notably during World War II. When Hitler was young he moved to a town named Vienna, this is where he acquiredRead MoreThe Holocaust : A Large Scale, State Sponsored, Systematic Murder Of Innocent Jews1327 Words   |  6 Pagespeople â€Å"The Final Solution†. Nearly six million out of the nine million European Jews were murdered in total. This means that two-thirds of the European Jewish population was wiped out in less than 10 years. Although Jews were the main target of the Nazi regime, others were viewed as inferior as well. These peoples included, Gypsies, Communists, Socialists, Jehovah s Witnesses, some Slavic peoples, and homosexuals. Today, we know that although the Germans did not succeed in their plan to annihilate

Hybrid Network Security Free Essays

ACCEPTED FROM OPEN CALL SECURITY ISSUES IN HYBRID NETWORKS WITH A SATELLITE COMPONENT AYAN ROY-CHOWDHURY, JOHN S. BARAS, MICHAEL HADJITHEODOSIOU, AND SPYRO PAPADEMETRIOU, UNIVERSITY OF MARYLAND AT COLLEGE PARK ABSTRACT Satellites are expected to play an increasingly important role in providing broadband Internet services over long distances in an efficient manner. Most future networks will be hybrid in nature — having terrestrial nodes interconnected by satellite links. We will write a custom essay sample on Hybrid Network Security or any similar topic only for you Order Now Security is an imporSSSL tant concern in such networks, since the session 2 Proxy satellite segment is susceptible to a host of attacks, including eavesdropping, session hijacking and data corruption. In this article we address the issue of securing communication in satellite networks. We discuss various security attacks that are possible in hybrid SSSL session 1 SSSL handshaking and satellite translation at client proxy (RPA) networks, and survey the different solutions proposed to secure data communications in these networks. We look at the perforMost future networks mance problems arising in hybrid networks due to security additions like Internet Security Prowill be hybrid in tocol (IPSec) or Secure Socket Layer (SSL), and suggest solutions to performance-related nature — having problems. We also point out important drawbacks in the proposed solutions, and suggest a terrestrial nodes hierarchical key-management approach for interconnected by adding data security to group communication in hybrid networks. satellite links. Security is an important concern in such networks, since the satellite segment is susceptible to a host of attacks, including eavesdropping, session hijacking and data corruption. INTRODUCTION With the rapid growth of the Internet, satellite networks are increasingly being used to deliver Internet services to large numbers of geographically dispersed users. The primary advantage of satellite networks is their wide broadcast reach — a satellite can reach users in remote areas where terrestrial connectivity is not available. Satellite networks are also easily and quickly deployed, and can be a more cost-effective solution in areas where laying ground fiber networks would be too expensive. Although satellite networks offer great potential, they also present significant challenges that need to be addressed. Security is becoming an increasingly important aspect of all network. In this article we focus on the challenges that need to be addressed in order to make satellite networks more secure while maintaining seamless interoperability with terrestrial networks. These security-related challenges include the following considerations: †¢ Satellite channels are wireless broadcast media, which makes it possible for an unauthorized user to receive the signal and eavesdrop on the communication, if it is not encrypted. †¢ Without proper security mechanisms, any sufficiently well-equipped adversary can send spurious commands to the satellite and jam or disrupt the communication. †¢ Satellite channels can occasionally have high bursty errors (for example, during heavy rain) that result in packet loss. Satellite networks also suffer from long propagation delays (for example, 0. 5 seconds for geostationary satellites). Therefore, security systems should add minimal delays to the communication and have mechanisms to recover from loss in security information. Incorporating security solutions originally designed for terrestrial networks, such as Internet Security Protocol (IPSec) or Secure Socket Layer (SSL), into satellite networks can cause severe performance penalties. In this article we consider some of these issues. We focus on data security for IP-based commercial networks, and discuss the performance problems that arise due to the encryption of the Transmission Control Protocol (TCP) header and payload when popular unicast security protocols like IPSec or SSL, originally designed for terrestrial connections, are applied to satellite networks without incorporating changes necessitated by the unique characteristics of satellite networks. We also look at the protocols proposed for secure group communication in hybrid satellite networks, and describe a hierarchical approach to group key management that is robust, scalable, and suitable for the characteristic topology of hybrid networks. The rest of the article is organized as follows. We describe the hybrid satellite-network topology and features that make it different from terrestrial networks. We discuss security needs for the hybrid network. We discuss the current approach to provide end-to-end unicast security in hybrid networks, and describe the performance problems arising as a result. We survey 50 1536-1284/05/$20. 00  © 2005 IEEE IEEE Wireless Communications †¢ December 2005 NOC Internet Gateway Proxy Client Proxy NOC (a) Internet Web server Web server (b) n Figure 1. Commercial direct-to-home network topology: a) case 1; b) case 2. the proposals for key management for secure group communication in satellite networks. We describe a possible solution to secure unicast communication without sacrificing performance and highlight our key-management approach to security for group communication in satellite networks. We conclude the article by pointing to future research directions. highly susceptible to the delay-bandwidth product and exhibits very poor performance in satellite channels. Satellite TCP connections need large transmit windows to fully utilize the available bandwidth. However, due to the TCP slowstart algorithm and large propagation delay in the satellite channel, it takes much longer for satellite TCP connections to reach the target window size, in comparison to terrestrial TCP connections. Also, the window is very vulnerable to congestion due to the multiplicative decrease strategy of TCP. The problem is compounded by the fact that TCP misinterprets link-layer corruption (which is the prevalent source of loss in satellite links) as congestion (which is rare) and consequently reduces the window. The PEP provides an efficient solution to the above problem. In satellite networks, a PEP agent is installed at the satellite gateway between the satellite network and the Internet. The PEP agent inspects every TCP packet that flows through the network. For data packets, the PEP sends back premature acknowledgments to the TCP senders, without waiting for the TCP segments to be actually delivered to the receivers. These premature acknowledgments are specially formatted to be indistinguishable from real acknowledgments and they considerably shorten the perceived round-trip delay. Studies have shown that this technique is critical for the performance improvement of satellite networks [2–4]. Hence, TCP PEPs have been widely deployed in satellite networks today. Commercial networks also employ HTTP proxy servers to improve the speed of responses to Web-browser requests. When a user browses through content on the Internet, the application layer protocol in use is HTTP. A typical HTTP exchange involves a request by the browser for a Web page (â€Å"GET†), and a response from the Web server, which contains the hypertext markup language (HTML) text of the requested Web page. A typical HTML page would also contain multiple embedded â€Å"objects† such as images, embedded media or scripts, and so forth. Each embedded object has to be retrieved with a separate HTTP request-and-response exchange. Therefore, a Web page that contains n – 1 embedded objects takes n * RTT time to load fully, where RTT is one round-trip time. This can be extremely costly in a satellite network, where the RTT is usually high. COMMERCIAL HYBRID SATELLITE NETWORK ARCHITECTURE The network topologies we consider are illustrated in Fig. 1. In both topologies, we assume that there is one geostationary satellite with multiple spot-beams covering a large geographical area. Each spot-beam covers a subset of the total user set. We assume that future satellites will have an IP stack, be capable of onboard processing, and switch the data between supported spotbeams. The satellite therefore acts as an IP router-in-thesky. The Network Operations/Control Center (commonly known as NOC or NCC) connects to the satellite through the hub satellite gateway. The NOC is also connected to the Internet through high-speed terrestrial links. Terrestrial users can be either standalone machines (Fig. 1a), or a cluster of machines at each location, such as a local area network (LAN) (Fig. 1b). Terrestrial LANs can be either wired or wireless. Each user or LAN is connected to a local satellite terminal. The users receive traffic from the satellite via the forward channel (satellite downlink). The users can also communicate with the satellite via the return channel (uplink). There is no terrestrial connectivity between the users or the LANs. Usually, in commercial satellite networks that transfer Internet traffic, a split-connection Transmission Control Protocol (TCP) Performance Enhancing Proxy (PEP) is implemented to reduce the negative effects of the satellite link on the Internet connection [1]. Satellite channels provide large bandwidth (which can be as high as 90 Mb/s in the downlink), but also suffer from long propagation delay in comparison to terrestrial links. The delay can be as high as 500 ms (round-trip) for a geostationary satellite link. The propagation delay can have a severe adverse impact on the delivery of Internet traffic. Most of the Internet traffic uses the TCP, which is IEEE Wireless Communications †¢ December 2005 51 SSSL encryption New IP header ESP Original TCP header IP header header TCP payload (SSL record) IPSEC encryption ESP trailer proxy (user side). There is a hub proxy server located at the NOC with the hub satellite gateway — this proxy server represents the gateway proxy for both TCP and HTTP performance enhancements. SECURITY THREATS Similar security attacks can be launched against different hybrid satellite network topologies, but the impact of attacks would differ depending on the type of network and the applications supported by the network scenario. In the following, we list some of the important security threats in the hybrid network described above, and highlight the importance of the threats for the different network scenarios. Confidentiality of information: For networks that require information privacy, a primary threat is unauthorized access to confidential data or eavesdropping. Since the satellite is a broadcast medium, any entity on the ground with the right equipment can receive the satellite transmission. If the data is broadcast in the clear, then adversaries can be privy to the information that is flowing in the network. Data confidentiality can be achieved by message encryption. This requires that the senders and receivers are concurrently aware of the correct cryptographic keys used in the encryption/ decryption operations. This is a twofold problem: the problem of selecting suitable cryptographic algorithms for doing encryption so that overall network performance is not affected, and the problem of coordinating keys between users, that is, key management. Sending spurious commands: An adversary with the right equipment can send spurious control and command messages to the spacecraft, thus making the spacecraft perform operations different from their intended use. This can disrupt legitimate operations and communication in the network. This attack can be prevented if the sources of the messages are properly authenticated by every receiver. This would require suitable mechanisms for authentication, such as digital signatures [5]. The level of security required would dictate the authentication policy, for example, whether only the end users should authenticate each other, or whether authentication should happen on a per-hop basis. The latter might be necessary for scenarios where the satellite should not broadcast spurious information. If the satellite authenticates the source of every message it receives, it will transmit only those messages for which source authentication occurs correctly. Message modification attack: When the traffic goes over open networks, an adversary who is listening on the path can intercept both control and data messages. The adversary can modify the messages and send them to the destination, which can be the spacecraft, the ground terminals, or the end users. When the message reaches the intended destination, it would think that the corrupt message is coming from the true source, but the message content might be different from that expected or required for normal network operation. Message modification can be prevented by SSL record HTML page n Figure 2. IPSec and SSL encryption on a packet. The HTTP proxy server (also known by various other names, depending on the vendor) is implemented in satellite networks to overcome this problem. In a typical implementation, this requires a local Web proxy server at each user location, and a remote proxy server at the central hub facility of the satellite network (i. e. , the NOC). The Web browser at the user location should be able to recognize the local proxy (which can be either software on the client machine, or a separate hardware connected inbetween the client machine and the local satellite terminal). When the browser makes a request for a Web page, the HTTP GET request is sent to the local Web proxy, which forwards the request to the destination Web server. The Web server responds with the requested base HTML page. This page is intercepted by the proxy server at the network hub facility. The hub proxy server reads the base HTML page and sends multiple GET requests to the destination Web server for all the embedded objects in the base HTML page. This exchange occurs over a high-speed terrestrial connection between the hub and the Internet, thereby saving the time each request would have needed for a round trip over the satellite link. As the objects of the Web page are retrieved by the hub, they are immediately forwarded to the proxy at the user location. As the user browser receives the base HTML documents, it generates appropriate GET requests to fetch the objects corresponding to the links embedded in the document. The browser GET requests are terminated at the Web proxy server, which forwards the prefetched documents to the user browser immediately. The net result is that only a single â€Å"GET† request from the user browser traverses the satellite link, while a set of rapid responses quickly deliver the requested Web page and associated elements to the browser. The need for satellite capacity is also reduced, which is the most costly element of a satellite network. In terms of the user’s experience, the user sees a brief pause after the original Web-page request (corresponding to the round-trip time it takes for the request to the forwarded to the destination server, and the response to be received by the browser, over the satellite link), followed by near-instantaneous delivery of all content residing on the requested page. The trade-off is additional hardware at the user location and the central-hub facility. In Fig. 1a, the proxy server at the user represents both the PEP (user side) and the HTTP 2 IEEE Wireless Communications †¢ December 2005 appending message-integrity check mechanisms to every message, for example, message authentication codes (MACs) [6] or digital signatures. Security requirements and policies can dictate whether message authentication should happen only at the communication end points, or whether interme diate nodes should also verify the integrity of every message. Denial-of-service attack: Some attacks on security can be facilitated if strong security mechanisms are put in place for performing message-integrity checks or authenticating users. Consider the case where the satellite does authentication and integrity checks on all messages before broadcasting. An adversary can send a large number of spurious messages to the satellite, thus making the satellite spend significant computational cycles processing the spurious messages, which could be better spent broadcasting legitimate messages. Since the satellite has limited processing power, such an attack can be very effective, especially if strong cryptographic mechanisms like digital signatures are used for authentication and message integrity. This is a denial-of-service (DOS) attack. Although this DOS attack can be launched against any node in a network, a satellite network can be particularly susceptible to such an attack, since the satellite is a single point of failure and can be easily overwhelmed if made to perform too much computation. New IP header ESP Original IP TCP header header header TCP payload ESP trailer Encryption with K1 Original IPSEC ESP tunnel mode encryption New IP header ESP Original IP TCP header header header TCP payload ESP trailer Encryption with K2 Encryption with K1 Layered IPSEC ESP tunnel mode incryption n Figure 3. IPSec and layered IPSec encryption. Key K1 is shared between endpoints only. Key K2 is shared between endpoints and TCP PEPs. 1 embedded objects takes n * RTT to be loaded, an increase in delay by a factor of n. IPSEC FOR SECURITY AT THE NETWORK LAYER Several proposals for data confidentiality and authentication in satellite networks call for use of IPSec, which has been widely adopted by the Internet Engineering Task Force (IETF) for security at the network layer. IPSec and SSL are used independently of each other. IPSec creates an end-to-end tunnel at the network layer for the secure transfer of traffic. The two end-points in the communication negotiate security parameters known as the security association (SA) before traffic can be encrypted. Once the SA has been established in the handshake phase, the IP packets are encrypted using the algorithms and the keys specified in the SA. This is done when the IP-encrypted security payload (IPSec ESP) [9] is used. The IPSec ESP provides for both data encryption and authentication. IPSec provides strong security for data confidentiality and authentication, but it has a heavy byte overhead — in the ESP mode, IPSec adds 10 bytes of overhead to the header and trailer. In addition, if authentication is used, ESP adds 16 bytes or more for the integrity check value, and another 8 bytes or more of initialization vector (IV) if the encryption algorithm uses an IV. Also, IPSec has been designed primarily to secure point-to-point communication; it s not well suited for group communication, due to the lack of the dynamic key-establishment procedure necessary to for secure communication in groups where the membership changes with time. In addition, IPSec does not allow for authentication at intermediate nodes, but this might be useful in some security situations. A widely researched problem when using IPSec in satellite networks is its inability to coexist with PEPs. The keys used for encryption in the IPSec ESP are known only to the two endpoints and therefore any intermediate node in the network cannot decrypt the traffic. IPSec ESP has two modes of operation — tunnel mode and transport mode. In tunnel mode, the entire IP packet is encrypted and a new IP header and ESP header are generated and attached to the encrypted packet (Fig. 3), which adds an extra SECURING END-TO-END UNICAST COMMUNICATION USING IPSEC OR SSL Research on satellite security has focused on using the existing standardized technology, originally designed for terrestrial networks, to fix well-known security holes in satellite networks. Two such protocols that are widely used for secure unicast communication are IPSec [7] and SSL [8]. Figure 2 illustrates the encryption regions of SSL and IPSec. SECURE SOCKET LAYER FOR SECURE WEB TRAFFIC The SSL protocol secures the Web-browsing connection on an as-needed basis. When the client requests a secure connection or the server demands one, SSL is activated to secure the HTTP connection. The resulting connection is popularly known as secure HTTP (or HTTPS) and it encrypts the application-layer HTTP data end-to-end between the client and the server. In the protocol stack, the SSL layer sits between the application and the transport layers. Therefore, SSL encryption hides the TCP payload from all nodes in the network, except the client and the server. SSL encryption does not allow the HTTP proxy to function correctly. The HTML Web page encrypted into the SSL records is readable only by the client and the server who have the decryption keys. The keys are not available to the proxy, and therefore the proxy cannot read the HTML Web page. Consequently, the hub proxy server cannot send requests to the Web server for the embedded objects in the page and, therefore, HTML object prefetching cannot take place. The net result is that a Web page with n – IEEE Wireless Communications †¢ December 2005 53 The HTTP proxy also cannot function when the IPSec ESP is used. Since the HTML page is encrypted end-toend, the HTTP proxy cannot read the Web page in order to prefetch the embedded objects. Therefore, use of IPSec leads to a severe degradation in performance for both the TCP PEP and HTTP proxy. SSSL translation at hub proxy (HPA) SSSL session 2 SSL session 3 Proxy Client Internet Gateway NOC SSSL session 1 SSSL handshaking and translation at client proxy (RPA) Proxy Web server Figure 4. The SSL Internet Page Accelerator concept for efficient HTTPS over satellite. 20 bytes of overhead in addition to the overhead mentioned above. Encrypting the original IP header provides very strong security by disabling attacks (such as traffic analysis, etc. ). In transport mode, the payload portion of the IP packet is encrypted and a new ESP header is attached to the packet after the original IP header, which is in the clear. In either mode, the IP packet payload, which includes the TCP header, is encrypted with keys known only to the end points. Therefore, a TCP PEP, which is an intermediate node in the communication path, cannot read or modify the TCP header, since the PEP does not know the keys. Consequently, the PEP cannot function, thus leading to degradation in the performance of the TCP protocol. The HTTP proxy also cannot function when the IPSec ESP is used. Since the HTML page is encrypted end-to-end, the HTTP proxy cannot read the Web page in order to prefetch the embedded objects. Therefore, use of IPSec leads to a severe degradation in performance for both the TCP PEP and HTTP proxy. It is important to note that the problems that arise from the use of the SSL protocol or the IPSec ESP are independent of one another. It is conceivable that both protocols are used simultaneously, for example, when a secure Web page is accessed via a secure VPN tunnel. However, in such cases the performance issues do not change and the effect would be equivalent to using the IPSec ESP alone. On the other hand, if SSL alone is used, then the performance would be better, since the TCP PEP can function correctly in this scenario. [10] and layered IPSec [11], the idea is to encrypt different regions of the IP packet using different keys (Fig. ). The TCP payload is encrypted with key K1, which is shared only between the endpoints. The original IP header and the TCP header are encrypted with key K2, which is shared between the end points and also with intermediate authorized nodes such as the TCP PEP. Therefore, the TCP PEP can decrypt the header portion of the ESP packet with K2 and read the TCP header to do its performance optimizations. But the PEP cannot read the TCP payload and thus cannot access the actual data, since it does not posses the key K1. The layered IPSec approach allows TCP PEPs to function effectively. However, the method does not solve the problem of HTTP proxy servers. The HTML page is encrypted with key K1 as part of the TCP payload, and K1 is not shared with any intermediate node. Therefore, the Web page is not accessible to the HTTP proxy and no object prefetching can be accomplished. Olechna et al. [12] have suggested two solutions to the IPSec problem. In the first approach, the paper proposes moving the TCP PEP gateways to the endpoints. The TCP optimizations are done on the traffic in the clear, and then the traffic is encrypted using IPSec. There is no TCP PEP at the satellite hub. This approach improves the performance, but when a packet is lost or received in error TCP goes into congestionavoidance phase and the transmission is reduced by half. The second proposed approach, which deals effectively with this problem, is to split the secure connection into two at the satellite gateway. One connection is between the client and the gateway, and the second connection is between the gateway and the Internet server. This allows the gateway to decrypt the IPSec packet and read the headers and thereby do performance optimizations. This requires trust in the satellite gateway, which can now read all the traffic. This might be unacceptable to users who require strong end-to-end security. Several modified TCP protocols have been proposed that perform better than the original specification in the event of channel errors or delay, or when IPSec is used. A discussion of PROPOSED SOLUTIONS TO MITIGATE PERFORMANCE PROBLEMS WITH SSL OR IPSEC Several proposals have been made in academia and industry to deal with performance problems that arise from using IPSec and SSL in satellite networks. The concept of breaking up IPSec encryption into multiple encryption regions or zones on a single packet has been proposed independently in [10, 11]. Although the finer details in the two approaches are different, the basic idea is the same. Known as multilayer IPSec (ML-IPSec) 54 IEEE Wireless Communications †¢ December 2005 Group keys (TEK) K1,8 Internal keys (KEK) K1,4 K5,8 Path of keys for M8 K1,2 K3,4 K5,6 K7,8 Leaf keys Members Group key K2 K1,12 Group key K1 K1,8 K9,12 K1 K2 K3 K4 K5 K6 K7 K8 M1 M2 M3 M4 M5 M6 M7 M8 (a) K1K2 K3 K4K5 K6 K7K8 K9 K10K11K12 M1M2M3M4M5M6M7M8 G1 G2 G3 G4 Members Gateways (b) Figure 5. Logical key hierarchy and its extension to satellite networks: a) with eight members; b) ML-IPSec integrated LKH tree with users and gateways. these TCP enhancements can be found in [13]. The problem of HTTP proxy performance when SSL is used has been addressed within the industry by breaking up the end-to-end single SSL connection between client and server into m ultiple SSL connections [14]. In this solution, the client browser creates a secure HTTP connection with the remote page accelerator (RPA) at the client satellite terminal, a second connection is created between the RPA and the hub page accelerator (HPA), and a third connection is between the HPA and the server (Fig. 4). The RPA performs all necessary handshaking with the client browser. The HPA can decrypt the SSL traffic from the server and perform the desired object prefetching. Taken together, this allows delivery of secure Web content with little performance degradation and with little change to the standard protocols. The major drawback to this scheme is that it requires a high level of trust in the intermediate nodes. The HPA, which is a third-party entity, can read all the sensitive Web traffic that passes between the client and the server. This might be unacceptable when absolute end-to-end security is desired. is O(logN) (where N is the number of members in the group), which is less than the O(N) keys required if the GC arranged the members in a flat topology. To allow PEPs to function correctly when network-layer security is used, [15] proposes the use of ML-IPSec. The paper proposes using a single LKH tree to manage the group key K2, used to encrypt the transport layer header (known to end users and trusted gateways), and the group key K1, known only to the end users and used for encrypting the transport layer data. As shown in Fig. b, users M 1 †¦M 8 are leaf nodes in a subtree of degree three, and gateways G 1 †¦G 4 are leaf nodes in a subtree of degree two. The root key of the member node subtree, K 1,8 , is used to encrypt the transport payload. The root of the overall key tree, K1,12, is used to encrypt the transport header. All member nodes know both K1,8 and K1,12, but the gateways know K 1,12 only (apart from the internal keys in the gateway subtree). How the LKH tree would be managed is not stated in [15]. This is important, since the users and the gateways might not be in the same administrative or security domain. The paper also considers all users and gateways as a â€Å"flat† network for key distribution purposes, rather than taking into account the hierarchical nature of the network topology. The use of LKH for key management in satellite links has also been proposed in [18], which suggests algorithms for dynamically managing the LKH tree in case of member joins and leaves. Duquerroy et al. [19] proposed â€Å"SatIPSec,† for key distribution and secure communication for both unicast and multicast in a satellite network. The solution is based on IPSec, with the addition of flat multicast key exchange (FMKE) to support key management for secure group communication. Management of SAs for both unicast and multicast communication is integrated into the FMKE protocol. FMKE also incorporates reliability mechanisms so as to guarantee reliable key distribution in the lossy satellite setting. However, FMKE manages SAs between the satellite terminals or gateways only and does not extend to the end users. Therefore, end-to-end security is not provided when using SatIPSec. The RPA performs all necessary handshaking with the client browser. The HPA can decrypt the SSL traffic from the server and perform the desired object prefetching. Taken together, this allows delivery of secure Web content with little performance degradation and with little change to the standard protocols. KEY MANAGEMENT PROPOSALS FOR SECURE GROUP COMMUNICATION IN HYBRID NETWORKS Some research has been done with individual algorithms that serve as tools in building keymanagement protocols in order to facilitate secure group communication in hybrid satellite networks. Howarth et al. [15] have proposed the use of logical key hierarchy (LKH) [16, 17] for efficient key management for multicast groups in a satellite network. LKH makes use of a centralized key manager or group controller (GC), which constructs a logical key tree with the group members as the leaves of the tree (Fig. 5a). The internal nodes of the tree are the key encrypting keys (KEK), which are used to securely transport key updates to the group. The root of the tree is the session key or traffic-encrypting key (TEK), which is used to encrypt the session traffic. The number of keys that need to be updated when a member node joins or leaves the group IEEE Wireless Communications †¢ December 2005 55 New IP header ESP Original TCP HTML header IP header header object links Base HTML page Encryption with K2 ESP trailer Encryption with K1 n Figure 6. Layered IPSec with modifications for HTTP optimization. Also, FMKE treats all the satellite terminals it services (which are called SatIPSec clients) in a â€Å"flat† topology, and establishes separate secure channels to all SatIPSec clients. This will not scale when there are a large number of clients. Also, SatIPSec does not consider the dynamic joins and leaves of members in the group communication setting; a client needs to be preauthorized for all the groups it wants to take part in. The protocol also requires complete trust in the group controller and key server (GCKS), which is a third party that is responsible for managing the SAs between the clients. All clients need to have preshared secrets with the GCKS. IPSEC AND SSL IN HYBRID NETWORKS: OUR APPROACH We look at separate solutions to the performance problem arising out of using SSL and IPSec in hybrid networks, and also consider how the two approaches can be combined. HTTP OVER IPSEC TUNNEL One viable method is to break up the end-to-end IPSec tunnel into multiple connections. This is similar to the solution proposed in [12]. But while their approach looks at only the TCP enhancements, we add the use of the HTTP proxy as well. In our approach, the IPSec connection from the client is terminated at the client proxy. The proxy creates its own IPSec connection to the gateway TCP proxy. A third IPSec connection is created from the gateway TCP proxy to the Web server. Schematically, this is similar to Fig. , with IPSec connections replacing the SSL connections in the figure. The IPSec handshaking between the client and the server is spoofed by the client proxy on the client end, and by the TCP hub proxy on the server end. In this model, the Web traffic can be read completely by the client proxy and the hub proxy. The two proxies are able to perform the TCP enhancements because they can read the TCP header. In addition, the hub HTTP proxy can perform HTM L object prefetching from the server because it can read the base HTML page as it is returned to the client on a HTTP request. When the client browser generates staggered requests for the embedded objects upon receiving the base HTML page, the client proxy is responsible for returning local acknowledgments to the requests, and sending all the objects to the client browser at one time. The design is therefore fully able to maintain the functionality of the TCP and HTTP proxies. It also encrypts the traffic so that it can be seen only by the client, the server, and the two intermediate proxy servers. The design also makes minimal changes to existing standard protocols. However, the design also requires that there be full trust in the proxy servers. Also, there is additional overhead in setting up three IPSec connections, as opposed to one (as in the end-to-end case). The overhead in encryption/decryption also increases by a factor of three for every IP packet, since the intermediate proxies need to decrypt the TCP header and the HTML content. When the security requirement is that the traffic be unreadable to intermediate nodes, the above approach will not work. In this situation, we propose extending the layered IPSec approach in order to allow portions of the HTML content to be also accessible to the proxy servers. Assume for layered IPSec that the keys are K1 and K2. K1 is known only to the client and the server, while K2 is known to the client, the Web server, and the intermediate proxy servers at the client and the gateway. When the client makes HTTP requests, the requests are encrypted using K2, so that the client proxy server can read the requests and send local acknowledgments. Additional software at the Web server parses the requested HTML page so as to obtain all the embedded object links. These object links are collated into a new HTML page that contains only the object links, and this new page is encrypted with K2. The base HTML page that contains all the information and the object links is encrypted with K1. Both the encrypted base HTML page and the encrypted object links HTML page are sent in reply. Therefore, the encrypted ESP packet looks as it is depicted in Fig. 6. Upon receiving the IPSec packet from the Web server, the hub proxy is able to read the object links (since it has K2) and therefore do prefetching for the embedded links. In addition, the hub proxy can also read the TCP header and perform TCP enhancements. However, the HTML base-page data cannot be read by the hub proxy, since it does not have K1. The encrypted base HTML page can only be read by the client when the IPSec packet reaches the destination. This design allows the TCP and HTTP proxies to perform effectively while maintaining a high level of end-to-end security. However, the security is not as strong as in traditional IPSec, since the intermediate proxies do get some information insofar as they can read the links of the embedded objects, even though they cannot read the application data. This is the major trade-off necessary to achieve acceptable performance in this design. In addition, the model requires changes to be made to the IPSec protocol so that layered IPSec is supported with the HTTP performance additions. A major issue in the above model is the handshaking mechanism required to set up the layered IPSec connection. To maintain a high level of security, we propose that the connection be set up primarily between the client and the server, who negotiate both K1 and K2, apart from other parameters of the security association. The handshaking mechanism then provides K2 securely to both the client and the hub proxy servers. The client and the hub proxy servers are required to authenticate themselves correctly before they can receive the secondary key or access the IPSec traffic. 56 IEEE Wireless Communications †¢ December 2005 DSSL main mode (K1) DSSL main mode (K2) Internet Gateway Proxy (K2) Client (K1, K2) NOC DSSL primary and secondary modes Original TCP IP header header Proxy SSL record Primary SSL record Proxy (K2) Web server (K1,K2) Encryption with K2 Encryption with K1 IP packet format for DSSL n Figure 7. Dual-mode SSL for HTTP optimization. HTTP OVER SSL When the HTTP traffic is secured using SSL only, and there is no IPSec tunnel in use, several approaches are possible to ensure acceptable performance. If the security requirement of the client and the Web server allow for trusted intermediate nodes, then the SSL accelerator concept of [14] can be a viable solution. This would require no change to the protocols at the expense of higher overhead in order to set up multiple SSL connections between the client, proxy, and Web server. When the security policy does not allow for trusted third parties, a different approach is needed. We propose the use of a modified SSL protocol, which we term dual-mode SSL (DSSL). As shown in Fig. 7, the secure connection in DSSL has two modes — an end-to-end main mode connection between the client and the Web server, and a secondary mode connection that has the hub HTTP proxy as an intermediate node. When secure HTTP traffic is requested, the DSSL main mode connection is first negotiated between the client and the server. As part of the handshake for the main mode, the client and the Web server also negotiate the parameters for the secondary mode. Let K1 be the encryption key for the main mode, and K2 be the encryption key for the secondary mode. The client transfers the parameters of the secondary mode to the client and hub HTTP proxy servers only after the proxy servers authenticate themselves to the client. When the client makes an HTTP request, the client proxy sends local replies to the client browser, as discussed previously. The Web server, on receiving the request, parses the requested HTML page to obtain the embedded object links, which are collated into a new HTML page. The object links HTML page is then encrypted by DSSL using K2 to create the proxy SSL record. DSSL encrypts the base HTML page using K1 to create the primary SSL record. The two records are appended together and sent to the client in an IP packet (Fig. 7). The hub proxy intercepts the IP packet, extracts the object links from the proxy SSL record using K2, and prefetches the embedded objects. The Web server always encrypts the actual objects using K1, so that the hub proxy cannot read the base HTML page data. The hub proxy transfers all the embedded objects together to the client at one time. Therefore, the HTTP proxy functionality is preserved in DSSL while maintaining the end-to-end security of the HTML page contents. However, the security is less than in the end-to-end SSL connection case, since the HTTP proxy can read the object links. In standard SSL, the proxy servers can read no part of the base HTML page, not even the object links. We believe this slight reduction in security is acceptable, given the considerable improvement in performance using this method. The DSSL design is more complex in comparison to SSL since it requires the creation of an additional connection, and therefore involves a higher overhead. There is also the added overhead of multiple encryptions and decryptions with two different keys, and the complexity of parsing the HTML page for the object links. All these require changes to the base SSL protocol. The DSSL concept is similar to the multiplechannel SSL concept proposed in [20]. However, the authors do not differentiate encryption in primary and secondary SSL records but instead suggest that HTTP traffic with lower security requirements be encrypted entirely with keys known to intermediate nodes. For our security requirements, that approach would not be acceptable. Differential Encryption in Single SSL Record — The use of a proxy SSL record is not necessary if various parts of the HTML page can be encrypted with The DSSL design is more complex in comparison to SSL since it requires the creation of an additional connection, and therefore involves a higher overhead. There is also the added overhead of multiple encryptions and decryptions with two different keys. IEEE Wireless Communications †¢ December 2005 57 Secondary SSL encryption Primary SSL encryption New IP header ESP Original TCP Proxy SSL header IP header header record Secondary IPSec encryption Primary SSL record ESP trailer Primary IPSec encryption n Figure 8. Packet format for dual-mode SSL with IPSec. different keys. In that case, the Web server can encrypt the object links in the HTML page with key K2 and the rest of the HTML page contents with key K1, thus creating a single SSL record with different encryption. The hub proxy server can parse the SSL record and decrypt only the object links with key K2, before forwarding the IP packet to the client proxy. We assume that the primary and secondary encryption keys K1 and K2 have been set up and distributed as described in the previous sections, with K1 known to the client and the Web server only, while K2 is known to the client, the Web server, and the intermediate proxy servers. A similar technique can be applied when IPSec encryption is used instead of SSL encryption. The advantage here is that the size of the packet does not increase, although there is the overhead of distributing key K2 to the proxy servers to be considered. HTTPS OVER IPSEC For the sake of completeness, we consider the situation where a secure Web page is requested over an IPSec tunnel. This method involves redundancy of resources, since use of SSL when IPSec is being used does not provide any substantially added security. However, our approach can take care of the performance in this scenario as well. In this situation, we propose integrating DSSL with layered IPSec. Then the secondary keys for both the layered IPSec connection and the DSSL connection are shared with the proxy servers. The secondary key for layered IPSec is shared with both the TCP proxy and the HTTP proxy. When layered IPSec encrypts the packet, the secondary key encryption extends up to the proxy SSL record. The TCP proxy servers can therefore decrypt the TCP header of the ESP packet, and the HTTP proxy server can decrypt the proxy SSL record. Consequently, performance optimizations for both TCP and HTTP are allowed without letting the intermediate servers read the HTML page. A schematic of the IPSec packet in this setting is shown in Fig. 8. A HIERARCHICAL APPROACH TO KEY MANAGEMENT FOR DATA SECURITY IN HYBRID NETWORKS In [21], we have proposed a key-management framework for distributing cryptographic keys securely and in a scalable manner to users taking part in group communication in a hybrid satellite network. The objective is to ensure data confidentiality, by encrypting the data traffic with group keys known to all the group members. The key-management framework is built on top of the multicast routing architecture. We have considered the hybrid network topology shown in Fig. 1b and designed a multicast routing architecture to allow users to communicate seamlessly between multiple terrestrial LANs (also referred to as subnetworks) [22]. Our routing design makes specific use of asynchronous transfer mode (ATM) point-to-multipoint routing [23] over the satellite links, and Protocol-Independent Multicast Sparse-Mode (PIM-SM) multicast routing [24] in terrestrial LANs. We have extended PIM-SM to allow multiple rendezvous points (RPs) in each multicast group. The satellite gateway in each LAN acts as the local RP for the LAN and creates the local multicast trees for group members within the LAN. The local multicast trees are connected together over the satellite links by using the ATM point-to-multipoint virtual connection, thereby creating one end-to-end multicast tree for each group, encompassing all the LANs with group members in them. The multicast routing architecture is thus adapted closely to the hierarchical network topology, and allows for building efficient multicast trees with low control and data overhead. The design of the key-management protocol is independent of the routing algorithm, although it is based on the same underlying principle, that is, a hierarchical breakup of the network based on the topology. We divide the network into two levels — the lower level, comprised of terrestrial LANs where the users are located, and a higher level consisting of the satellite, the NOC, and the satellite gateways or RPs in each LAN, which together form an overlay (Fig. 9a) interconnecting terrestrial LANs. The RPs act as the â€Å"bridge† between the two levels. Key management is done separately in the two levels. In each LAN we introduce a local group controller (called the â€Å"subnetwork key controller† or SKC) to manage the keys for all groups active in the LAN. The SKC is responsible for access control of all members of all groups that are active in its LAN, generating the group keys for all local groups, and updating the keys on group-member joins and leaves when a group is active. The keys managed by an SKC are entirely local to its LAN, and do not affect the key management in any other LAN in the network. The SKC uses the LKH algorithm to manage keys in its LAN, creating a logical key tree that we term the SN Tree. Each group active in a LAN has its own SN Tree. The leaves of the SN Tree for a group correspond to the longterm shared secrets between the SKC and the local users in the LAN who are active as sources and/or receivers in the group. The root of the SN Tree corresponds to the session key that is used for encrypting the group traffic within the LAN at any particular instant. On member joins and leaves, the session key, and all the keys on the path from the root to the leaf node corresponding to the member joining/leaving, are updated, while all other keys in the SN Tree remain unchanged. The overlay has its own key management, 58 IEEE Wireless Communications †¢ December 2005 Overlay RP tree root key Level-1 Satellite Overlay network NOC Gateway Gateway Gateway SN tree SKC RP (root) RP (leaf) SKC RP tree RP (leaf) Gateway Level-0 SKC Subnet n Subnet 1 Subnet 2 (a) Subnet 3 Subnetwork Subnetwork (b) Subnetwork n Figure 9. A hierarchical approach to key management in hybrid networks: a) hierarchy in the hybrid network; b) tiered tree key management. also based on the LKH algorithm. At the overlay level, the key management for a particular group is controlled by the satellite gateway/RP (known as the root RP for that group) of the LAN that has group sources active for the longest continuous period in the group. The logical key tree for any group thus formed at the overlay is termed the RP Tree. The root RP is responsible for generating keys for the RPs of the LANs who subscribe to the particular group, that is, have sources and/or receivers active in the LAN. Each group has its own RP Tree. The design ensures that the NOC cannot receive/transmit data to any active group, unless it explicitly subscribes to the group as a member node. However, LANs joining any particular group initially register with the NOC, which maintains a group membership table for all active groups, so that at all times the NOC is aware of the LANs which are participating in all active groups. The NOC is also responsible for selecting the root RP of the RP Tree for each group, which it does based on the earliest-to-join policy. The root RP also might be different for different groups, since the LAN with the longest continuously active sources might be different for different groups. Our algorithm has the provision to allow the root RP for any group to change — this happens if the currently active root RP leaves the group, when all sources/receivers within its local LAN cease to participate in the group. Our algorithm therefore builds a hierarchy of logical key trees that closely follow the hierarchy in the network topology, as shown in Fig. 9b. We term this framework Tiered Tree-based Key Management. In this hierarchy of key trees, the gateway RPs are responsible for performing key translation on all the multicast group traffic as it transmits the data from local sources to receivers in remote LANs, or when it receives group traffic from remote sources for local receivers. This translation is necessary since the data traffic is encrypted with the RP Tree session key in the overlay, and with the SN Tree session ey within the local LAN, with the two session keys being independent of one another. The detailed design of Tiered Tree-based Key Management, analysis of its security, and experimental results can be found in [25]. The primary objective in our design is to minimize the amount of key-management control traffic n Figure 10. Tiered tree framework: total key management traffic vs. RP tree traffic for three groups (Y-axis shows the traffic in bytes per second; X-axis is the simulation duration in minutes). hat flows over the satellite links, due to the long delay involved as well as susceptibility to channel errors. We have attempted to ensure that the security of the data traffic does not add any overhead in terms of delay other than that absolutely unavoidable, and that the security protocol does not contribute to deadlocks in group-data dissemination where some group members in certain LANs cannot read the data due to having wrong keys. From the simulation results, Fig. 10 shows the reduction in key-control traffic over the satellite links using our tiered-tree approach. The graph compares the total key-management IEEE Wireless Communications †¢ December 2005 59 Our solution is a generic solution aimed specifically at multicast key management and does not deal with an end-to-end security solution for secure communication or give any implementation specifics. information sent in the network for three simultaneous groups (i. e. , sent over the RP trees, sent over the satellite links, and all SN trees limited to local LANs), to the total key information sent on the RP trees (satellite links) only. As the graph shows, the resource savings on the satellite links is substantial when the tiered-tree scheme is used. Even though the group dynamics are high, the amount of message exchanges are very few in the RP tree, that is, over the satellite links. If a flat key-management hierarchy had been used instead, the total key-management traffic would have been sent over the satellite links, thus leading to increased delay and increasing the possibility that the correct keys do not reach all the members at the same time. Our solution is therefore very scalable. It also acknowledges the fact that the group members might be located in different security domains and, therefore, a single network-wide security management might not be possible. This is a more realistic scenario, since terrestrial LANs might be individual company domains, while the satellite overlay infrastructure is usually owned by a separate entity that provides network connectivity to the LANs, and is not responsible for generating the network traffic. This framework addresses the problem that all users might not be visible to a single, centralized security authority, and the dynamics of user joins or leaves in one LAN should not create an overhead to users in other LANs. Also, in widearea satellite networks we consider that the satellite channel conditions at a given point in time might be different in different sections of the network. There might be loss in information due to bad channel conditions in some network segments; however, this should not disrupt communication in network segments where the channel conditions are better. Solutions which treat all users in a single tree will not be able to perform as robustly under such conditions. Our solution is also similar to the ML-IPSec concept in that the satellite terminals are only partially trusted; they are allowed to do partial decryption/encryption of the IP packets for efficient routing. However, it is a generic solution aimed specifically at multicast key management and does not deal with an end-to-end security solution for secure communication or give any implementation specifics. approaches for typical topologies and validating the proposed designs by simulation. Lastly, we have described our hierarchical approach of key management for providing data security in hybrid networks. We are continuing our research in this area and examining designs to integrate our keymanagement protocol with the unicast case. A considerable amount of work needs to be done with regard to secure protocols for hybrid networks, specifically for the case where users are mobile. Here we have touched upon only a small subset of the problems. None of the proposed solutions, including our own, address the question of user authentication or message integrity for group communication. However, we believe the security problems discussed here will receive further treatment from the research community, and this work will be a useful contribution to the field. ACKNOWLEDGMENT The authors would like to thank the anonymous reviewers for their valuable comments and suggestions. The research reported here is supported by the National Aeronautics and Space Administration (NASA) Marshall Space Flight Center under award no. NCC8-235. The views expressed in this article are solely the responsibility of the authors and do not reflect the views or position of NASA or any of its components. REFERENCES [1] J. Border et al. , â€Å"Performance Enhancing Proxies Intended to Mitigate Link-Related Degradations,† IETF RFC 3135, June 2001. [2] V. Arora et al. , â€Å"Effective Extensions of Internet in Hybrid Satellite-Terrestrial Networks,† University of Maryland, College Park, Tech. Rep. CSHCN TR 96-2, 1996. [3] V. Bharadwaj, â€Å"Improving TCP Performance over HighBandwidth Geostationary Satellite Links,† University of Maryland, College Park, Tech. Rep. ISR TR MS-99-12, 1999. [4] N. Ehsan, M. Liu, and R. Ragland, â€Å"Evaluation of Performance Enhancing Proxies in Internet over Satellite,† Wiley Int’l. J. Commun. Sys. , vol. 16, Aug. 2003, pp. 513–34. [5] NIST, â€Å"Digital Signature Standard (DSS),† May 19, 1994. [6] H. Krawczyk, M. Bellare, and R. Canetti, â€Å"HMAC: KeyedHashing for Message Authentication,† IETF RFC 2104, Feb. 1997. [7] R. Atkinson and S. Kent, â€Å"Security Architecture for the Internet Protocol,† IETF RFC 2401, Nov. 1998. [8] IETF Transport Layer Security Working Group, â€Å"The SSL Protocol Version 3. 0,† Nov. 1996, available at http://wp. netscape. com/eng/ssl3/draft302. txt [9] R. Atkinson and S. Kent, â€Å"IP Encapsulating Security Payload (ESP),† IETF RFC 2406, Nov. 998. [10] Y. Zhang, â€Å"A Multilayer IP Security Protocol for TCP Performance Enhancement in Wireless Networks,† IEEE JSAC, vol. 22, no. 4, 2004, pp. 767–76. [11] M. Karir and J. Baras, â€Å"LES: Layered Encryption Security,† Proc. ICN’04, Guadeloupe (French Caribbean), Mar. 2004. [12] E. Olechna, P. Feighery, and S. Hryckiewicz, â€Å"Virtual Private Network Issues Using Satellite Based Networks,† MILCOM 2001, vol. 2, 2001, pp. 785–89. [13] P. Chitre, M. Karir, and M. Hadjitheodosiou, â€Å"TCP in the IPSec Environment,† AIAA ICSSC 2004, Monterey, CA, May 2004. 14] SSL Accelerator, Spacenet Inc. , available at http://www. spacenet. com/technology/advantages/ssl. ht ml [15] M. P. Howarth et al. , â€Å"Dynamics of Key Management in Secure Satellite Multicast,† IEEE JSAC, vol. 22, no. 2, 2004, pp. 308–19. [16] C. Wong, M. Gouda, and S. S. Lam, â€Å"Secure Group Communications Using Key Graphs,† IEEE/ACM Trans. Net. , vol. 8, 2000, pp. 16–30. CONCLUSION Security is a critical component in hybrid IPbased satellite networks. In this article we have focused on some of the challenges that lie ahead. We have discussed the unique characteristics of hybrid satellite networks that make the problem of ensuring secure communication different from that of purely terrestrial networks. We have presented a survey of the various security solutions that have been proposed, and discussed their advantages and disadvantages. We have proposed several approaches to solve the performance problems of TCP and HTTP in satellite networks arising from secure communication. However, a lot of further work needs to be done to validate our approaches, and we are in the process of developing specific detailed security 0 IEEE Wireless Communications †¢ December 2005 [17] D. Wallner, E. Harder, and R. Agee, â€Å"Key Management for Multicast: Issues and Architectures,† IETF RFC 2627, June 1999, available at http://www. apps. ietf. org/rfc/ rfc2627. html [18] G. Noubir and L. von Allmen, â€Å"Security Issues in Internet Protocols over Satellite Links,† Proc. IEEE VTC ‘99, Amsterdam, The Netherlands, 1999. [19] L. Duquerroy et al. , â€Å"SatIPSec: An Optimized Solution for Securing Multicast and Unicast Satellite Transmissions,† 22nd AIAA Int’l. Commun. Sat. Sys. Conf. and Exhibit, Monterey, CA, May 2004. [20] Y. Song, V. Leung, and K. Beznosov, â€Å"Supporting Endto-End Security across Proxies with Multiple-Channel SSL,† Proc. 19th IFIP Info. Sec. Conf. , Toulouse, France, Aug. 2004, pp. 323–37. [21] A. Roy-Chowdhury and J. Baras, â€Å"Key Management for Secure Multicast in Hybrid Satellite Networks,† 19th IFIP Info. Sec. Conf. , Toulouse, France, Aug. 2004. [22] A. Roy-Chowdhury and J. Baras, â€Å"Framework for IP Multicast in Satellite ATM Networks,† AIAA ICSSC 2004, Monterey, CA, May 2004. [23] G. Armitage, â€Å"Support for Multicast over UNI 3. 0/3. 1 Based ATM Networks,† Internet RFC 2022, Nov. 1996. [24] S. Deering et al. , â€Å"The PIM Architecture for Wide-Area Multicast Routing,† IEEE/ACM Trans. Net. , vol. 4, no. 2, 1996, pp. 153–62. [25] A. Roy-Chowdhury, â€Å"IP Routing and Key Management for Secure Multicast in Satellite ATM Networks,† Master’s thesis, University of Maryland, College Park, 2003, available at http://techreports. isr. umd. edu/reports/2004/ MS2004-1. pdf Paper Award, 2004 WiSe Conference. He holds three patents. His research interests include wireless networks and MANET, wireless network security and information assurance, integration of logic programming and nonlinear programming for trade-off analysis, multicriteria optimization, noncooperative and cooperative dynamic games, robust control of nonlinear systems and hybrid automata, mathematical and statistical physics algorithms for control and communication systems, distributed asynchronous control and communication systems, object-oriented modeling of complex engineering systems, satellite and hybrid communication networks, network management, fast Internet services over hybrid wireless networks, stochastic systems, planning and optimization, intelligent control and learning, biologically inspired algorithms for signal processing, and sensor networks. MICHAEL HADJITHEODOSIOU [M] received an M. A. (honours) in electrical and information sciences from the University of Cambridge, United Kingdom, in 1989, an M. S. in electrical and computer engineering from the University of California, Irvine in 1992, and a Ph. D. n engineering (specializing in satellite communications) from the Centre for Satellite Engineering Research (CSER) at the University of Surrey, United Kingdom, in 1995. Among his awards are a scholarship award for studies at the University of Cambridge from the Cambridge Commonwealth Trust (1984–1986); a Fulbright Scholarship for post-graduate work in the United States (1989–1991); a Research Fellowship from the U. K. Engineering and Physical Sciences Research Council (EPSRC) (1992); and the Canadian National Science and Engineering Research Council (NSERC) post-doctoral fellowship award (1995). He worked as a research fellow in the Communication Systems group of CSER (1991–1995) and spent a year as a visiting fellow at the Canadian Government Communications Research Center (CRC) (1995–1996). In November 1996 he joined the Center for Satellite and Hybrid Communication Networks (CSHCN) at the Institute for Systems Research, University of Maryland, College Park, where he is currently an assistant research scientist. He is an expert on space communications and satellite networks. His research interests include performance optimization of wireless and hybrid networks, security and protocol support issues for satellite systems, and design optimization of next-generation broadband satellite networks and applications. He is currently working on supporting the communication needs of NASA enterprises and the communication architecture enabling space exploration. He is currently serving as secretary of the IEEE Satellite and Space Communications Technical Committee. SPYRO PAPADEMETRIOU received his B. S. in computer science from George Mason University, Fairfax, Virginia. Since then he has been actively involved in Internet research and development within both industry and academia. He was the principal Internet researcher at Synectics Corp. , where he developed network and database software. He worked as a researcher at the University of Maryland’s Institute for Systems Research, where he designed and developed their first networking laboratory, which is part of the CSHCN. At Inktomi Corp. he spearheaded client acceleration research and was a member the content-distribution network design team. These resulted in several patent filings, of which he holds one. The latter also resulted in American Online’s Web client accelerator product. Currently he is with Orbital Data Corp. working on network and application optimization. His research interests include network optimization, application optimization, satellite and terrestrial wireless networking, delay-tolerant networks, sensor networks, distributed systems, and network software architecture. We have touched upon only a small subset of the problems. None of the proposed solutions, including our own, address the question of user authentication or message integrity for group communication. BIOGRAPHIES AYAN ROY-CHOWDHURY (ayan@isr. umd. edu) received his B. E. in electronics and telecommunications engineering in 1998 from Jadavapur University, India, and his M. S. in electrical engineering in 2003 from the University of Maryland, College Park, where he is currently a Ph. D. student. Between 1998 and 2000 he worked as a senior software engineer at Wipro Technologies, India. His research focuses on the design of protocols and frameworks for secure communication in hybrid networks. He is working on secure protocols for unicast and multicast routing in networks that have wired and wireless terrestrial components interconnected by satellite links. He is also looking into key management techniques for secure data transmission for these network architectures, and efficient user-authentication mechanisms for the same. As part of these topics, he is also investigating performance problems for network communication in satellite networks when security is involved. J OHN S. B ARAS [F] received a B. S. in electrical engineering from National Technical University of Athens, Greece, in 1970, and M. S. and Ph. D. degrees in applied mathematics from Harvard University in 1971 and 1973, respectively. He was founding director of the Institute for Systems Research (one of the first six NSF Engineering Research Centers) from 1985 to 1991. Since August 1973 he has been with the Electrical and Computer Engineering Department and Applied Mathematics Faculty at the University of Maryland, College Park. In 1990 he was appointed to the Lockheed Martin Chair in Systems Engineering. Since 1991 he has been director of the Center for Hybrid and Satellite Communication Networks (a NASA Research Partnership Center). Among his awards are the 1980 Outstanding Paper A How to cite Hybrid Network Security, Papers

Edgar Degas Paintings Comparison and Analysis Essay Example For Students

Edgar Degas Paintings Comparison and Analysis Essay They were artists who were dissatisfied with Academic Art and opposed the Romantics idea that the main reason for art was to create emotional excitement for its viewers. Edgar Degas was one of these rebels and one of the most prominent members of the group. Degas became known for his description of his subjects, which included depictions of ballet dancers and woman bathing Which portrayed the Impressionist label Of experimental and vivid use of color. L As seen throughout many of his paintings, Degas consistently is seen to observe %undresses, milliners and ballet dancers at work. He employs in his artwork unusual perspectives and complex formal Structures. His works, Dancers, in Pink and Green and Woman Combing Her Hair are bon in particular pieces that are well-known and clearly depict the Impressionist details of Degas. Both are very familiar in style, and in symbolism as well. Dancers in Pink and Green and Woman Combing her Hair are two of hundreds of Degas pieces. They have sign ificant similarities in style, mostly in part because they both reflect Impressionist artistic details. The charm of these two pictures are abstract- consisting in rhythm of light and shade, color and went. Degas uses oil on canvas for Dancers, in Pink and Green. The vibrant colors, especially pink and green, are prominent in the painting and portray to the viewer a natural view of the ballerinas. The ballerinas appear natural and spontaneous rather than having a build up of composition with well- studied proportions and balance. Edgar Degas goal was to create a simple yet appealing image to the eye. Although Edgar Degas ignored details, revealed brushstrokes and placed unblended colors side by side, he still created a very realistic image of the ballerinas If a viewer were to take a few steps back from he painting, the image itself seems to fall into place and seems real and intricate. His unusual perspectives and complex Structures present in his artworks are also seen in his Woman Combing her Hair. Edgar Degas created M/Oman Combing Her Hair With pastels on a light green wove paper. The pastels helped establish a simple in theme, but complex in Structure, composition. He depended upon Vivid colors and purposeful gestures in his paintings rather than precise lines. 3 These characteristics added to the depiction of the subject of the painting. As seen in the previous Dancer art ice, the natural image of a woman is portrayed, but in this case it is a woman combing her hair. There is no build up of composition with studied proportions or balance as well- it is an image merely off naked woman combing her hair. The animal being that takes care of himself, a cat that licks itself. Up to this moment, the nude has been presented in poses that had a public in mind; my women, on the other hand, are simple honest people who bother with nothing but the very caring Of their Degas)4 This quote reflects upon his view as an Impressionist artist. He did not want to portray his bowmen as fixed poses that are established to create an image Of a typical womans stance in the public m ind, but to just provide the audience with a natural woman performing the mere routines of caring for her body. Within the two paintings, Degas expressed and categorized these women according to their profession: whether they be dancers or regular women of the household. They represented specific types of individuals,5 Although completely different in themes, both paintings relay a similar message that not only characterizes Degas paintings, UT characterizes Degas himself. It is evident through the collection tot his works that Edgar Degas has developed obsessions, especially with woman in different forms, In these two cases, the women are either dancers or are regular woman performing daily routines such as combing hair. .u80b1600fa6b47884245d8f064c6aaa63 , .u80b1600fa6b47884245d8f064c6aaa63 .postImageUrl , .u80b1600fa6b47884245d8f064c6aaa63 .centered-text-area { min-height: 80px; position: relative; } .u80b1600fa6b47884245d8f064c6aaa63 , .u80b1600fa6b47884245d8f064c6aaa63:hover , .u80b1600fa6b47884245d8f064c6aaa63:visited , .u80b1600fa6b47884245d8f064c6aaa63:active { border:0!important; } .u80b1600fa6b47884245d8f064c6aaa63 .clearfix:after { content: ""; display: table; clear: both; } .u80b1600fa6b47884245d8f064c6aaa63 { display: block; transition: background-color 250ms; webkit-transition: background-color 250ms; width: 100%; opacity: 1; transition: opacity 250ms; webkit-transition: opacity 250ms; background-color: #95A5A6; } .u80b1600fa6b47884245d8f064c6aaa63:active , .u80b1600fa6b47884245d8f064c6aaa63:hover { opacity: 1; transition: opacity 250ms; webkit-transition: opacity 250ms; background-color: #2C3E50; } .u80b1600fa6b47884245d8f064c6aaa63 .centered-text-area { width: 100%; position: relative ; } .u80b1600fa6b47884245d8f064c6aaa63 .ctaText { border-bottom: 0 solid #fff; color: #2980B9; font-size: 16px; font-weight: bold; margin: 0; padding: 0; text-decoration: underline; } .u80b1600fa6b47884245d8f064c6aaa63 .postTitle { color: #FFFFFF; font-size: 16px; font-weight: 600; margin: 0; padding: 0; width: 100%; } .u80b1600fa6b47884245d8f064c6aaa63 .ctaButton { background-color: #7F8C8D!important; color: #2980B9; border: none; border-radius: 3px; box-shadow: none; font-size: 14px; font-weight: bold; line-height: 26px; moz-border-radius: 3px; text-align: center; text-decoration: none; text-shadow: none; width: 80px; min-height: 80px; background: url(https://artscolumbia.org/wp-content/plugins/intelly-related-posts/assets/images/simple-arrow.png)no-repeat; position: absolute; right: 0; top: 0; } .u80b1600fa6b47884245d8f064c6aaa63:hover .ctaButton { background-color: #34495E!important; } .u80b1600fa6b47884245d8f064c6aaa63 .centered-text { display: table; height: 80px; padding-left : 18px; top: 0; } .u80b1600fa6b47884245d8f064c6aaa63 .u80b1600fa6b47884245d8f064c6aaa63-content { display: table-cell; margin: 0; padding: 0; padding-right: 108px; position: relative; vertical-align: middle; width: 100%; } .u80b1600fa6b47884245d8f064c6aaa63:after { content: ""; display: block; clear: both; } READ: Burial Of Count Orgaz By El Greco EssayHe is a keen observer to women and has cultivated complete objectivity in his paintings for he catches complete natural spontaneous poses of his subjects, These poses were very controversial at the time because it exposed women in an uncommon way- a nude portrayal of them just in the means of their home. It could be interpreted that Degas took regular woman routines, and added sexual depictions to them on purpose so that from then on, a woman combing her hair could be then be imagined as a Woman combing her hair naked. As seen in Dancers, in Pink and Green, Degas reveals a simple image Of multiple dancers getting ready to perform, and one in-particular dancer is just staring at her feet while others are prepping for the performance. This simple depiction has more complex meaning in that the dancers are typically portrayed dancing. However, in this case, Degas shows one often just staring t her feet. Not dancing yet. Dance depicts structure, for and predetermined actions- a contradiction to his ideal of natural spontaneous poses. In Woman Combing Her Hair, the image is obviously simple. Woman performing a daily routine, This indicates clearly that Edgar Degas seems to pay much attention to womens actions in detail. The ballet dancers and naked woman are like a film sequence of women in his collection. They are neither delirious or romantic figures, but instead are objects tot obsessed study of their working movements and intimate daily activities, Both Dancers, in Pink and Green and Woman Combing He r Hair were painted to portray a very natural feel, as if the viewers have come upon the scene without the knowledge of the people engaged in it. Quality of Illimitableness and elasticity is evident, and this suits the expression of movement and life in the paintings. Every appears to not to be premeditated, but an instantaneous impression, unlike a camera because the action isnt suspended- it retains elastic rhythm of moving life. Within these two pieces of art, Edgar Degas is seen to put emphasis on certain aspects. In the case of the ballet dancers, emphasis is placed on the dancers costumes through their vivid color and size in comparison to the dancers body. They seem to stand-out from the body in the painting. Degas ballet dancers have no beauty in the face or grace Of figure in an ordinary sense. Rather, the beauty of the painting is depicted through the vibrant unblended colors of the pink and green costumes. The colors Of the costumes, although they are very visible, are simultaneously related to the background colors- the natural colors Of the scenery in the painting. In Woman Combing Her Hair, emphasis is prominently placed upon the the length and color of the womans hair. The painting is dominated by light colors such as light vibrant green, and the white rug and the soft skin tones; however, the hair seems to be the prominent feature of the image that catches the eye the most. Its length and dark luscious color grab the viewers attention and draws them to the focus: the woman combing her hair. Like the ballet dancers in Dancers, in Pink and Green Degas does not make an attempt to conceal the physical activity of this woman. Without seeing the womans face, it is difficult to identity her beauty tort he has purposefully concealed it so that emphasis could be placed on the action and artistic expression rather than the details. This also applies to the Dancers, in Pink and Green painting. This unusual angularity was common in many of Degas pieces- it was a distinct characteristic of his innovative composition. He received many of his ideas from Japanese Print Art- this type of art heavily influenced his paintings; and his paintings and art style has in-turn influenced the artists following him.