The resistance in a conductor Essay Example for Free

The resistance in a conductor Essay This will consequently increase the resistance of the wire. However if the wire was shorter, the free electrons will not collide with the atoms as much as it did when it was longer. So now I can conclude that resistance is directly proportional to length and that if the length of the wire doubles its resistance doubles. If I draw a graph representing current against voltage for different lengths of wire, then it will look like this: The shortest wire of these will be the steepest in the graph; this is because it has the least resistance and therefore supplied the least voltage. The longest wire will have the greatest resistance and will be represented by the lowest line on the graph. Material of the wire: Here I use two different materials for the wires and calculate their resistance. I have chosen copper and nichrome. I will use the same procedure as mentioned before to calculate the resistance and I will set up the apparatus as first mentioned while keeping the thickness and the length of the wires same. If I were to draw a graph representing current against voltage, for this experiment it will look sort of like this: Thickness of the wire: Resistance: Resistance and length: If I plot a graph to show how resistance varies with length, it will show me something similar to this predicted graph: The graph passes through the origin, which concludes that , however much I increase the length, the resistance will increase by the same amount. Resistance decreases if the cross-section area is increased. An example can help to get a clearer picture; a narrow wire has fewer paths existing for the electrons to move through. While a larger wire has many more paths they could take. This makes conduction easier. It can be shown that the relationship between the cross-section area, A and resistance is R ? 1/A OR R ? K/A Where k is a constant that depends on the length and type of material. If I plot a graph to show how resistance varies with area, this will be shown: Unlike the graph for length, the line doesnt pass through the origin. However: R ? 1/A means that a graph of R against 1/A will show direct proportion. If I plot a graph to show how resistance varies with 1/Area, I will get this: Free electron conducting in metal Conductors: Conductors ( e. g. copper, aluminum ) are those substances which easily allow the passage of electric current through them. It is because there are a large number of free electrons available in a conductor. In terms of energy band, the valence and conduction bands overlap each other as shown below. Due to this overlapping, a slight potential difference across a conductor causes the free electrons to form electric current. Thus the electrical behaviour of conductors can be effectively explained by the band energy theory of materials. Prior test In order to rely on my results, I take the readings of the current for the increasing and the decreasing currents; giving a prior test. Material: Length: Thickness: Resistance (? ) Average Current (mA) Current (decreasing in voltage) Current (increasing voltage) Voltage (V) Sly. Experiment This first trial is to test the accuracy and the realism of the experiment itself. It also shows us that as the temperature has an effect on resistance. I will use a 100cm long strip of Nichrome wire and attach it to the circuit and the current will be raised and recordings will be taken at different levels. 1. Attach 100cm Nichrome wire. 2. Turn on the power supply and raise the current. 3. Take reading from the voltmeter. 4. Continue raising the power recording voltmeter readings. This above procedure will require the following equipment given below: 1. 100cm Nichrome wire 2. Ammeter 0 to 200 mA 3. Voltmeter 0 to 20 volts 4. Rheostat 5. Crocodile clips 6. Battery 7. Switch with key 8. Connecting wires By adjusting the rheostat the voltage are increasing in steps of 0. 15 V to 0. 50 V. Each time noting down the corresponding ammeter readings. I do this to make sure the readings of the ammeter while increasing and decreasing the voltage are the same almost with a slight variation, therefore making sure that no heating has taken place. I will then note down the ammeter readings while decreasing the voltage in steps of 0. 50 V to 0. 15 V, and Ill take the average current readings as this will improve the reliability of my experiment. I will use a table similarly to the one drawn and record my readings and calculate the resistance. Material: Nichrome Wire Length: 100cm Thickness: 0. 45mm Resistance (? ) Average Current (mA) Current (decreasing in voltage) Current (increasing voltage) Voltage (V). Sly. No Average = 5. 70 And now I will draw a graph representing current against voltage, and then I will take the line of best fit from which I will take the gradient and check whether the results I have obtained graphically matches the results in the table. Obtaining Evidence In this part of my task, I will show all my graphs and results that I have obtained after carrying out the experiments. I have done the same process as I have planned earlier. My experiment will be based on these:   Length (same thickness and different lengths)   Thickness (same length and different thickness). Resistors in series Resistors in parallel Different Lengths Material: Nichrome Wire Length: 100cm Thickness: 0. 45mm mA Resistance (? ) Average Current (mA) Current (decreasing in voltage) Current (increasing voltage) Voltage (V) Sly. No Material: Nichrome Wire Length: 75cm Thickness: 0. 45mm mA Resistance (? ) Average Current (mA). Current (decreasing in voltage) Current (increasing voltage) Voltage (V) Sly. No   Average = 6. 49 Material: Nichrome Wire Length: 50cm Thickness: 0. 45mm mA Resistance (? ) Average Current (mA) Current (decreasing in voltage) Current (increasing voltage) Voltage (V) Material: Nichrome Wire Length: 25cm Thickness: 0. 45mm mA Resistance (? ) Average Current (mA) Current (decreasing in voltage) Current (increasing voltage) Voltage (V) Sly. Resistance = 1/440 = 0. 00227 x 1000 = 2. 27 Different Thickness Material: Nichrome Wire Length: 100cm Thickness: 0. 90mm mA Resistance (? ) Average Current (mA) Current (decreasing in voltage) Current (increasing voltage)Voltage (V) Sly. No Material: Nichrome Wire Length: 100cm Thickness: 0. 45mm mA Resistance (? ) Average Current (mA) Current (decreasing in voltage) Current (increasing voltage) Voltage (V) Sly. No Average = 8. 40 Material: Nichrome Wire Length: 100cm Thickness: 0. 56mm mA Resistance (? ) Average Current (mA) Current (decreasing in voltage) Current (increasing voltage) Voltage (V) Sly. Average = 4. 86 Material: Nichrome Wire Length: 100cm Thickness: 0. 32mm mA Resistance (? )Average Current (mA) Current (decreasing in voltage) Current (increasing voltage) Voltage (V) Sly. NAverage = 8. 73 Resistance from graph Thickness: 93 Material: Nichrome Wire Length: 100cm and 50cm Thickness: 0. 45mm mA Resistance (? ) Average Current (mA) Current (decreasing in voltage) Current (increasing voltage) Voltage (V) Sly.   Average = 12. 79 Resistance from graph 100cm and 75cm Gradient = y/x = 25. 15/0. 40 =62. 87 Resistance = 1/62. 87 = 0. 01590 x 1000 = 15. 90 100cm and 50cm. Gradient = y/x = 23. 55/0. 30 = 78. 5 Resistance = 1/78. 5 = 0. 012738 x 100 = 12. 73 Parallel Material: Nichrome Wire Length: 100cm and 75cm Thickness: 0. 45mm mA Resistance (? ) Average Current (mA) Current (decreasing in voltage) Current (increasing voltage) Voltage (V) Sly. Average = 3. 69 Material: Nichrome Wire Length: 100cm and 50cm Thickness: 0. 45mm mA. Resistance (? ) Average Current (mA) Current (decreasing in voltage) Current (increasing voltage) Voltage (V) Sly. No Resistance   Analyzing Evidence. Here in this part of my experiment I will prove that my hypothesis and my obtained results obey the ohms law. This is where the results from my graphs and the results I have already obtained earlier will be compared; talking about its proportionality. Variation in length: When the length of the wire boosts, the amount of atoms present in it also boosts. The variation of these atoms block the passage of electrons passing through the wire. A slower flow of electrons will therefore lead to less current passing through the wire hence the longer the wire, the longer the electrons have to travel, so they come across more collision. From this statements I predict that the resistance increases with the length of the increasing wire. Hypothesis: It is expected that the resistance should increase in proportion to the length. The resistance should be considerably higher for the 100cm length than it is for the 50cm length. Theoretically the resistance for the 100cm length should be 2 times that of the 50cm length. The reason for this was explained earlier. Resistance will increase with length. Resistance is proportional to length. In this table below I will show the results I have obtained from the graph and the table: ? R/L = constant Average R (graph)R (table) Length of wire (cm). From the above table I have concluded that resistance increases with length and as the length doubles, the resistance doubles about with it. The column R/L is roughly constant. This supports my hypothesis that resistance of a wire is directly proportional to its length. The even increase of resistance with length can be explained by the clashes that take place in a wire as current flows through it. When the current flows through a wire, the free electrons collide with the atoms of the wire. The longer the wire the more collisions occur. And this will result in an increase in the resistance. However, the shorter the wire, less the collision, hence less resistance. I will show the relationship between length of a wire and its resistance on a graph, from the values of the above table. And this will confirm my conclusion that length is directly proportional to its resistance. Results The resistance is clearly increasing as the length of the wire increases. And when the length of the wire doubles, its resistance also doubles. The results shown in graph is exactly what is anticipated to happen as stated in the hypothesis. From the table above we can see that as the length doubles, the resistance also approximately doubles. In the last column R/L if found to be constant somewhat, therefore making it obey the ohms law R ? L The predicted graph drawn between R and L looks like this: Variation of thickness This experiment is needed to confirm that the resistance of a wire is inversely proportional to its diameter. If the cross-section of a wire is enlarged this means that the area on which the electrons move will be enlarged. Thus suggesting that there will be no clouds of electrons and atoms. The current can travel easily with nothing increasing the resistance. Likewise if the wire is narrower the obstruction will be crossed by the electrons will be lesser and therefore the current will decrease. Hypothesis It is expected that the thinnest wire will have the highest resistance because a thicker wire offers less resistance to current than a thinner one of the same material. This is because current consists of electrons flowing through the metal of the wire. The electrons hop from atom to atom in the metal in reaction to the electric field in the circuit. A conductor with a larger cross-section allows more electrons to intermingle with the fields.

Issues Concerning African Americans and Puerto Ricans Essay Example for Free

Issues Concerning African Americans and Puerto Ricans Essay There are four major ethnic, cultural and racial groups present in the United States today. These groups which compose the nation’s population are the African Americans, Asian Americans, Hispanic and Native Americans or the Non-Hispanic Whites. From the dawn of time, issues of racial profiling have haunted the American Society, although United States of America is said to be the birthplace of patriotism unity and believed to be a nation that will adhere to intense dedication to freedom, justice and equality (Feagin, 1978). The vast diversity of the American population which characterizes the nation’s inhabitants has often resulted to disorder and chaos, as discrimination exists across the nation. Although the government has taken some actions and laws have been made and are implemented, they are not enough to counteract the racism problem at hand which is deeply rooted in the American tradition, as a longer time may deemed necessary before the public become accustomed to a racial free society. If the authorities are keen on abolishing and eliminate racial discrimination, it then important that they see to it that the public would have a better understanding and background of the different ethnic and minority groups. Awareness to their values, customs and traditions are small little steps that may eventually lead to these groups coexistence. For this reason, the paper discusses two of the major groups that play important roles in shaping the United States social structure, the African Americans and the Puerto Ricans. The emergence of Africans Americans or the black Americans population, which are United States residents but with blood lineage from the black racial group of Africa, in the United States can be traced back way before 1800’s as majority of black Americans have their descendants in the United States. While White Americans came to the United States voluntarily, their Black counterparts were not given a choice as majority of the black population came in America as slaves (Feagin, 1978). It is noting to know that among the different ethnics group that come and settled in the United States, African Americans are the only group which have come not in accordance with their own free will. They were used as servants in large agricultural fields. It was believed that the first African American that had entered the borders of the United States settled in Jamestown. Their slavery and the hard labors they performed served as their free passage to the United States as they are compared to English poor people. However during the great American Civil War, by virtue of the proclamation signed by President Abraham Lincoln, the Emancipation Proclamation, African Americans became free. But then the post war era, the restoration period, calls for the segregation of blacks from the whites and deteriorates what was supposed to be period of new beginning for the blacks.. In order to free themselves of troubles and violence brought by discrimination, most Black Americans followed the law which dictates racial segregation. However, as violence related to racial discrimination became widespread, calls for abolishing the racial profiling laws also intensify as growing African American heritage and intellect became more evident. The era of civil rights movement which aimed to promote camaraderie and embed equality by eliminating racial discrimination help largely to the Black Americans cause of seeking dignity for their culture and race. Thus, when the Black Power Propaganda was formed a more complex ideology was born as African American seeks for moral dignity, fairness, justice and freedom from white oppression. Today, free from slavery and contributing vastly to economics and politics and enjoying a legal status, Black Americans have enjoyed a great deal of success as they experienced and enjoyed greater rights, far from what were their ancestors have before. However, complete satisfaction and recognition of their rights will have to wait for another few years as white people and custom is still the dominant culture in the United States. The radical change, however, which started from the nineteenth century are strong indications and evidence of the emerging power the African Americans are obtaining. African Americans now have greater access top higher educations and growth in employment as blue and white collar workers are also evident. Disparity between the poverty of black and people have also reduced and many black Americans now have there owned home. However, the sad part is although continuous improvements are achieved each day, black Americans are still at disadvantage with the white people. It can be observed in issues regarding health insurances and benefits and institutional racism, which is very much present especially in middle school’s class. In fact, a report in Rutherford country showed that massive complaints of racial discriminations are filed as parents are alarmed with the growing numbers of black students that are suspended. Compare to their white counterparts, black students continue to be suspended at much higher rates, raising the question of racial discrimination in imposing discipline among the students. In 2006 for instance, 14. 4 % of black students were suspended in the district, which causes a handful of students to lag behind their studies (Scott, 2007). On the other hand rate of suspension for white students stand at 6. 6% (Scott, 2007). Figures and numbers indicate that the rates at which black students are suspended are more than double of the rate at which whites are. This then has poses an alarmed to the black population as their children are put into a disadvantage situation. Just like the African Americans, Puerto Ricans suffer a great deal of oppression and poverty as they occupy the bottom most part of the United States’ social hierarchy for years (Feagin, 1978). They are considered as one of the world’s poorest groups, however, Puerto Rico posses a great link to the Caribbean world and the developing counties across the globe, which the United States social failed to utilize for their own advantage as it failed to realize its importance to the nation. The emergence of the Puerto Rican Ethnic group dates back to the time when the island which was then named as Borinquen, was a colony under the rule of Spain. For 400 years, Spain uses it as a strategic base. The island was a home for different tribes of Taino, however as the Spanish settle with in the island, population of the Indian tribes gradually diminished as generations passed by. Disappearance was due to the fact that Spain used them for forced labor in mines -which causes natives to acquire disease, massive exterminations and racial intermingling and merging. During that time, where in slavery was widespread, large number of African Americans was brought to Puerto to replace the natives as workers. Thus, the present genetic component of a modern Puerto Rican is a mix of Spanish, native Indians and African American. In 1898, as Spain succumb to American power during the Spanish-American War it surrendered Puerto Rico to the United States. Americans deemed Puerto Ricans as ignorant and as result, self governing was denied to them and Puerto Rico become entirely dependent to the US government. Puerto Ricans were left confused politically and culturally as they desperately ask matters about the issue of their citizenship. US Congress however, denied them of acquiring US citizenship relating that Puerto Ricans and Americans should not be treated as equal and they are inferior compare to them. But a year before the US plunged into the World War I, it granted Puerto Ricans US citizenship. With the booming population and stagnant economics, Puerto Rico became one of the poorest countries around the globe in the 1940’s. In an effort to escape the harsh reality of life in the island, many of the population migrated to the United States, bringing with them the hope and the promise of an American Dream. However, the situation would not be different, as immigrants would fail to land jobs and are exploited. Furthermore, housings were prioritized for Native Americans. Language handicapped was also a barrier, which leads to them being discriminated. Puerto Ricans are also identified with Catholicism and Christianity which is teaching based from Spanish colonial times, and since the structure of the American church is Protestant, conflicts often arise. Businessmen of Puerto Rico descends, would often complain of the difficulty in getting loans. With automation starting to engulf the business and industrial sections, Puerto Ricans further sink to the bottom of the social pyramid as they become more isolated, like the black people. There were no opportunities that were presented for them as they lack the skills to land jobs. But then came the era of being unrest, the emergence of Civil Rights Movement and Anti-Poverty Groups in the 1960’s helped Puerto Ricans stimulate and assimilate into the American society, culture and politics (Nash, 2000). The movement and program covers every Puerto Rican and led to astounding solutions to the problems that result from ethnics and cultural differences and inconsistencies which are related to the failure to be in accordance with the dominant American Culture. The emergence of theses groups had opened the eyes of the Puerto Rican public to seek for fair and just treatment and uphold their dignity. Although they have been successful in appealing for changes, after decades of struggling for political representation, culture and customs respect and their placed into the American Society, Puerto Ricans are today just slowly beginning to achieve and realize the progress and results. Whether it is questions about citizenship status, welfare and housing programs, bilingual and multi-cultural education or electoral power, Puerto Ricans had stood the test of time and has proven it is capable of complex assimilation to the dominant American society. However for Puerto Ricans and other ethnic minorities and racial group in America, being subordinate to the dominant American culture is a continued struggle as still they are treated unjustly. References Feagin. J. (1978) Racial and Ethnic Relations. Englewood Cliffs, NJ Prentice-Hall. p. 212, p. 298 Scott, B. (2007). Daily Race Colors Suspensions. News Journal Murfreesboro. Nash, K. (2000). Contemporary Political Sociology: Globalization, Politics, and Power. Blackwell Publishers.

Development of Cryptography Studies

Development of Cryptography Studies 0.1 Abstract This report is an overview of some structures that have heavily influence the course and study of Cryptography the last decades. Initially, we will analyse the structure of some important ciphers such as DES, 3DES and AES by underlying some dark and complicated points and emphasizing the critical  functions called S-boxes. We will then expand of some basic attributes of these block ciphers, for example the running time of them and their hardware and software performance. Finally, we will focus on a highly important aspect of these cryptosystems, security by exploring some of the most significant attacks that have been discovered against them. The paper is concluded with a presentation of the most important results of our investigation. 1 Introduction Cryptography has a very rich history, rooted back in the ancient years. Even Greeks of classical times have demonstrated understanding of ciphers, with the example of Herodotus to be the most well known, who tattooed a message to his slave head on a slaves shaved head and hide it under his regrown hair. Before the modern era, cryptography had an absolute target the achievement of confidentiality of a message. The most crucial years for cryptography were undoubtedly the last century. The decisive step was an investigation of Claude Shannon, the father of information security. In his seminar at 1949, Shannon analysed and illustrated block ciphers and suggest that, if they are combined with some operations that can provide the whole cipher with permutation and substitution, they should be a reasonable option. A block cipher, is an encryption scheme that belongs in the branch of Cryptography that is called symmetric-key Cryptography. This name is justified by the fact that the parties th at are involved in the communication through the cipher use the same secret key. Later designed as iterated product ciphers, block ciphers are deterministic algorithms that operate on fixed length groups of bits, called blocks. The major attribute for a block cipher is that the length of the input, called plaintext, and the length of the output, called ciphertext, is always the same. They take as an input a key of k-bits length and the this key is expanded to many different keys following a sequence of operations, the so called round keys. Typically, a block cipher is built by iteration, using a function called round function. In every round, the round function takes as an input the corresponding message and the round key and produces a new outcome which is oriented to be used in the next round. The final round will produce the ciphertext. Block ciphers have been widely used and dramatically influence the new era of humanity, and more importantly for commercial reasons in industry a nd banking. There is a remarkable variety of examples from block ciphers, although for the rest of this paper we will focus on the most famous examples that dominated the whole area of symmetric-key Cryptography in the new era. These are called DES, 3DES, AES. Blowfish has also attracted the attention since there isnt still any known vulnerability but it will remain outside of the scope of this report. 2 Analysis and Description 2.1 Data Encryption Standard (DES) Nowadays, DES is considered to be insecure, but it had a huge impact in the development of the symmetric-key cryptography for many decades after its invention. It has been designed back in 1976, when the government of the United States realized the overwhelming necessity of an algorithm that could effectively protect government data and safely used for buying products from the international markets. The most interesting difference of DES with its predecessor, Lucifer, which has been designed by Horst Fiestel, is that the key length and the block length has been reduced significantly. Nevertheless, the key length, especially, was from the time that DES was published, under heavy criticism and was actually badly broken in 1997 with the so-called exhaustive search attack. That means that a machine was able to search all the possible keys and find the correct one. DES has a very rich history of attacks and we will examine some of these attacks in more detail later in this paper. The core idea behind DES is the so-called Feistel Network, where a block cipher can built up with the use of some arbitrary functions f0,f1,fd : {0,1}n → {0,1}n. There is a wide variety of block ciphers that have a similar construction, although AES has a completely different construction. The critical point in these kinds of constructions is the structure of these functions, which can vary significantly. Abstractly speaking, the main target is to construct an invertible function F : {0,1}2n → {0,1}2n in order to able to decrypt the ciphertext. DES is basically a 16-round Fiestel network. More specifically, the input is exactly 64 bits, so R0 and L0 are 32 bits each. Obviously, from the diagram above, in every the half of the bits remains unchanged. The other half comes with a sequence of operations. Initially, as specified by the protocol, a permutation of the whole input takes place, followed by a 16-round Fiestel Network. Each function f0,f1,f16 : {0,1}16 → {0 ,1}16 that is used at each round is computed by using the corresponding subkey, fi(x) = F(ki,x) ,in order to make the decryption circuit feasible and manageable from a hardware perspective of view. This subkey is produced by the main key, in the following way: 56 bits are selected from the 64 bits that contains the key, the 56 bits are divided into two 28 bit halves and each half is treated afterwards separately. In every round, both halves are rotated form the left to the right by one or two bits and then 48 bits are selected, 24 from the left and 24 from the right to build the corresponding subkey. After these 16 rounds of the Fiestel network, there is one more permutation before the final output is computed. The following image describes the construction of the fi function. Initially, the input of 32-bits replicates 48-bits with some simple calculations and then the result is XOR with the 48-bits subkey. The 48-bits are splitted to 8 blocks of 6 bits and passed to the S-boxes. This is the most critical point of a block cipher and bad implementation of S-boxes can easily compromise security. A S-box is a function {0,1}6 → {0,1}4 and acts like a look-up table. The selection of these tables is of vital importance and has been a controversial matter for many years. It has been proved that linear S-boxes is definitely not an option. Even a partly linear S-box can run under some kind of attacks. After the implementation of all the S-boxes, a last permutation that maps the 32-bits around, takes place. The decryption circuit follows exactly the inverse procedure. Obviously, the encryption and decryption circuit are almost identical as the only actual difference is the order that the f1,f2,,fd functions are applied. This fact made DES very attractive to hardware developers because they had to implement just one algorithm for both procedures. 2.2 Triple Data Encryption Standard (3DES) As already mentioned, DES has been proved to be vulnerable under certain types of attacks so significant has been made in order to improve the security of DES. For this reason, DES has been replaced by 3DES, which was published in 1998 To begin with, let E : KXM → M be a block cipher and lets define the function 3E : K3 → M as 3E((k1,k2,k3),m) = E(k1,D(k2,E(k3,m))), where D denotes the decryption algorithm. Actually, there are three encryption steps. The main question that arises here is why the middle one is a decryption algorithm and not and encryption algorithm. The answer is simple; this would have lead to the implementation of a single DES, beacause the first and the second DES operations cancel out. will cancel the other. Obviously, the key-size, as it was intended, has been increased to 168-bits, as each of the keys is 56-bits. There are three options for keys; in the first key options all the keys are independent, in the second option k1andk2 are independent and k3 = k1 and in the third all three key are identical, k1 = k2 = k3. The third option is no longer recommended by the NIST( National Institute of Standards and Technology), the first key option is the strongest with a total number of 168 key bits as mentioned above, and the second option is stronger that simply implementing DES twice. 2.3 Why not double DES? 3DES is considered to be a secure block cipher. Nevertheless, a normal question is why 2DES in not an option, as it may not seem easy to beak by brute force with a key-length space 2112. A 2DES can be defined in the following way; 2E(k1,k2),m) = E(k1,E(k2,m)) with a key length 112 bits. This construction turns out to be completely insecure and the reason for this is the meet-in-the-middle attack. Basically, if an attacker has at his disposal an actual message and the corresponding ciphertext, which will be of the same length, he will try to find a pair of key (k1,k2) that E(k1,E(k2,M)) = C. If we apply at both parts of this equation the decryption algorithm, then we get the get E(k2,M) = D(k1,C). So, the attacker will try to figure out which is the appropriate pair of key in order to map the message M and ciphertext C at the same point this also justifies the name of the attack meet-in-themiddle. The attack is structured in two steps: Firstly, the attacker has to build up a table wi th all the 2112 keys and the corresponding encryptions and then sort this list, and secondly, for all possible key that belongs to {0,1}56, he calculates D(k,C) and he looks for a match at the previous table. Whenever he finds the first match, his goal has been achieved. The running time of this attack is 256log(256) + 256log(256) < 263, time that is much smaller than the time that is necessary for brute force attack. 2.4 Advanced Encryption Standard(AES) It is widely acceptable AES has been adopted by the U.S. government and nowadays is used worldwide. As DES was proved insecure and 3DES quite slow, the demand for a more effective encryption scheme grew rapidly and at 1997 NIST requested a new proposal. After some investigation, NIST chose Rijndael as AES at 2000, a cipher that was designed in Belgium. AES, unlikely to its predecessor, its not a Feistel Network. In contrast, it is called a substitution-permutation network because both actions of permutation and substitution take place. AES has a fixed block size of 128-bits, although the key length can vary, 128,192 or 256 bits. Additionally, in every round of AES all bits change while in every round of DES half of the bits remain unchanged. Generally, a substitution permutation networks initial input is operated with an XOR with the corresponding round subkey, then goes through a substitution layer where there are some blocks, configured depending on what the substitution table says and finally a permutation layer follows where all bits are permuted. This procedure is repeated many times until the final outcome is produced. All steps of a substitution permutation network must be reversible in order to be able to decrypt. Specifically for AES, the 128-bits, which are equal to 16-bytes, are handled with the help of a 4X4 matrix with ten repeated rounds to follow. Each element of this matrix is one byte. Each byte comes under the XOR operation with the corresponding round subkey, and then a function is applied in every round that consists of three steps: (1) The Sub-Bytes step, according to which all bytes are replaced with other coming from a look-up table, named Rijndael S-box. This S-box is associated with the Galois Field(28) which is considered to have goo properties. This is a critical operation for the overall structure, as it provides AES with non-linearity. (2) The Shift-Rows step, where the last three rows of the current state are moved some certain positions to the left while the first row remains stable and (3) the Mix-Columns step, where all the bytes of each column of the current state are combined under a linear transformation. The last two steps provide AES with diffusion, a vital property for a secure cipher according to which if we change one bit of the plaintext then almost half of the bits o f the ciphertext will change. It is also considerable that the step Mix-Columns is omitted at the last round of AES. Each subkey is produced by the main key with some kind of expansion similar to the DES. The key expansion is introduced with a number of operations named rotate, Rcon, and S-box and then follows an inner loop in key schedule before the final subkey is produced. 3 Comparison and Attacks 3.1 Running time A real concern about which algorithm is appropriate, especially for commercial use, is the effectiveness and its running time. In general, the larger the block size is, the faster is the algorithm, obviously because larger amount of data is encrypted in one round of operations. Similarly, the smaller the key size is, the faster is the encryption algorithm, because the less key bits are involved in the operations and thus the complexity of them is reduced. A series of experiments have taken place to verify which of the famous encryption algorithms, AES,DES,3DES. Most of these experiments implement these encryption algorithms in Java, although there are some others that used C, most of them at a machine of Pentium 2 or Pentium 4. At most of these experiments, the fastest of these algorithms has been proved to be DES, followed by AES and finally from the 3DES, as it is three times slower than DES. It obviously doesnt make sense to examine the running time of these block ciphers in compl ete isolation with the security that they provide although it is definitely a factor that must be taken into consideration. 3.2 Software and Hardware Implementation Another important aspect that must be examined is the performance of these block ciphers in combination with the available hardware. Again, a lot of study has been carried out and provide us with some clear evidence. In compact architecture, 3DES, DES and AES have displayed very similar performance. In contrast, in high-speed architecture, AES is considered to be almost 4-times than the 3DES and DES. This is happening due to a variety of reasons, amongst them there is no hardware support for DES in modern CPUs, when from the other side there is for AES in increasingly many CPUs, including most targeting servers; hence hardware DES is oà ¯Ã‚ ¬Ã¢â‚¬Å¾oaded to a distant IC, when AES is often in-core. Additionally, DES is often used in CBC mode which makes parallelization inevitable and processed in advance during encryption when AES is mainly used in CTR mode where the possibility of parallelization is available. Finally, DES, and its expansion 3DES is much slower in software than AES, obviously because it was designed back at 1976 before the 8086 processor was designed and uses a lot of bit operations that are not implemented suà ¯Ã‚ ¬Ã†â€™ciently in a processor with a word oriented instruction set. 3.3 Attacks on DES and 3DES As already mentioned earlier at this paper, 2DES has been collapsed from the meet-in-the-middle-attack. Simultaneously, DES, despite its contribution to the overall development of cryptography, has also been defeated by a quite popular attack named exhaustive search. Exhaustive search means that the attacker will search the whole key space and he will find the appropriate, which is unique, in suà ¯Ã‚ ¬Ã†â€™cient amount of time. There are some cases, even in the real world where the attacker can obtain some pairs (mi,ci), where m denotes a message and c the corresponding ciphertext. Under this small requirement, DES was badly broken. To be specific, a company named RSA, back at 1997 announced a problem with the name DES challenge. The company announced six ciphertexts and in parallel announced the first three actual messages and asked for the scientific community to search for the key and use it to obtain the other messages. The same year of the request the challenge had been solved. To go further, the rapid hardware  development was able to create a machine that find the key and solve the problem, equivalently crack DES, within less than one day at the year 1999 with exhaustive search, leading to the assumption that 56-bits length block ciphers should not be used any more. As DES is one of the most famous and controversial block ciphers, it is not entirely surprising that there is a variety of attacks developed against DES, some of them even faster than exhaustive search. Back at 1998, Kocher and Jun demonstrated a very innovative idea by making a side channel attack, introducing a new era for cryptography. Side channels attacks extract information from the physical implementation of the cipher. This type of attack was specifically against smart cards, and is based in power measurement. They actually measured precisely the running time of the smart cards and analysed the diagrams that they obtain from this measurement. In this way, they were able to learn wa s much time was consumed by in each operation from the smart card and find exactly the key. Nowadays, even smart cards are equipped with mechanisms that dont reveal any information of the power consumption there is an attack called differential power analysis, which can steal the secret key after running a lot of time the smart card. It should me mentioned that these attacks are quite general and not for smart cards. In addition, there is another type of a quite highly surprising class of attacks called fault attacks. In this occasion, the attacker can cause a malfunction to a mechanism, lets say to a smart card, for example by warming it up. If he manage to cause and recognise an error at the last round of DES he will be able to discover the secret key. The last attack that we would like to point out is the so called linear cryptanalysis. This is a generic attack and was introduced by Matsui at 1993 and is one of the most realistic, sophisticated and quick attacks on the DES. His a ttacks, and generally in linear cryptanalysis, one tries to find probalistic linear relations between the plaintext, the ciphertext and the secret key. He starts by examining linear relations at the S-boxes of one round and if he succeeds, he will use the to find out linear relations in one-round and then finally them iteratively to find multi-round relations. These relations from round to round are not independent. By combining all these linear relations, the attacker should be able to retrive the secret key. Matsui attack used 244 known plaintexts to find 13 bits of the secret key with a high probability . A similar method was applied to find another 13 bits and then for the remaining 30-bits he applied exhaustive search, he applied exhaustive search, reducing significantly the time that the initial exhaustive search demands. Today, linear cryptanalysis is considered to be, with some improvements, one of the most powerful attacks on DES. Although DES is considered to be faultless and no specific technical vulnerabilities has been found, a high level of linearity at the fifth box of DES has created the possibility for someone to generate this type of attack. Most of the previously referred attacks can also be implemented against 3DES, as the two block ciphers are obviously, highly related. To begin with, an exhaustive search is not suà ¯Ã‚ ¬Ã†â€™cient any more as the key space, if we use three totally independent keys, is huge, especially if we take into consideration the computational power that a strong mahine can demonstrate nowadays. The meet-in-the middle-attack can be applied in a very similar mode, as the attacker can still create a sorted table with the first implementation of DES between one element of the table and the implementation of twice the DES at the opposite direction. The time needed for this attack is 2112, which is considered to be a high level of security, as nowadays a satisfactory level of security against a certain attack is approximately 290, although is still faster in comparison with exhaustive search. Lately, a new attack against block ciphers has been displayed, mainly intended against 3DES and Blowfish and exploits well known kind of vulnerabilities like collision and birthday attacks. Since this is currently under examination and was published only this year, we are not going to expand more. Overall, till today there is not a known and widely acceptable attack that cracks 3DES in a reasonable amount of time. 3.4 Attacks on AES Rijndael has outplayed all other candidates suggested for the AES and so has been analysed quite a bit the last decade. A lot of attacks have been introduced although none of them has hurt AESs security significantly. To begin with, there is a lot of analysis around the meet-in-the-middle attack and some possible improvements of it over the last five years. Gilbert and Minier have proved a very interesting distinguishing property for the first four rounds of AES with the following proposition; lets consider a set of 256 plaintexts where the entry a11 takes all byte values between 0 and 255 exactly once over a given set of plaintexts and all other entries are equal to a constant. If we encrypt this set with three rounds of AES then the function that maps a11 to C11 is determind by 9 fixed 1-byte parameters. C11 denotes the byte values at row i, column j. This proposition was used by them to implement the same idea of the meet-in-the-middle attack. Some further investigation have shown that the number of the parameters, and specifically for 13 or 14 bytes, and this is able to be reduced so the number of the required plaintexts will be minimized. Another famous class of attacks are called cache attacks. Cache is a small part of high speed memory and it aims to keep the CPU as much busy as possible. The catch parameters influence the running time of an algorithm. Specifically, when an element of a data array is called, then we have two possible outcomes. Id the element lies n the cache memory,then the access is instant. In a different situation, the element must be accessed from the main memory. This operation will be executed in significantly different running times and reveal valuable information. We can separate this class of attacks into three families; cold start misses, which arise for the first reference of the data, capacity misses which the magnitude of the element is bigger than the size o the cache and the conflict misses, which may happen in the case of accessing recently accessed data. 4 Conclusion In this paper we examined the structure of popular block ciphers that heavily influenced the development of Cryptography, like DES,3DES and AES and we have compared them in means of running time and software and hardware implementation. We have also considered some basic attacks that have been applied on these cryptosystems. We come to the conclusion that AES is the most safe and practical block ciphers, and this is justified by the fact that is has been chosen for encryption at a series of important applications nowadays. IS it estimated that AES will fully replace 3DES until 2030. There is not any doubt that AES is the most practical and convenient cipher from a hardware and running time perspective. Nevertheless, further investigation must definitely be carried out to ensure the the safety of AES, especially under the increasing enhancement of the technological means, is guaranteed. Finally, the attack Sweet32 is a newly invented attack and must carefully be examined, mainly becau se it is really compromise 3DES security, countermeasures must be taken DES will fully replaced by AES. 5 References [1] Dan Boneh and Victor Shoup, A Graduate Course of Cryptography, August 2015. [2] Diaa Salama Abd Elminaam,Hatem Mohamed Abdual Kader and Mohiy Mohamed Hadhoud, Evaluating The Performance of Symmetric Encryption Algorithms, Higher Technological Institute 10th of Ramadan City, Egypt, (Received Feb. 16, 2009; revised and accepted May 12, 2009) [3] Aamer Nadeem, Dr M. Younus Javed, A Performance Comparison of Data Encryption Algorithms, Department of Computer Engineering, College of Electrical and Mechanical Engineering, National University of Sciences and Technology, Rawalpindi, Pakistan. [4] Akashi Satoh and Sumio Morioka, Hardware-Focused Performance Comparison for the Standard Block Ciphers AES, Camellia, and Triple-DES, Tokyo Research Laboratory IBM Japan Ltd. [5] Huseyin Demirci, Ihsan TaskÄ ±n, Mustafa Coban, and Adnan Baysal, Improved Meet-in-the-Middle Attacks on AES, 2011. [6] Daniel J. Bernstein, Cache-timing attacks on AES, Department of Mathematics, Statistics, and Computer Science (M/C 249) The University of Illinois at Chicago, 2005. [7] Eran Tromer, Dag Arne Osvik and Adi Shamir, Computer Science and Artificial Intelligence Laboratory, Massachusetts Institute of Technology, 32 Vassar Street, G682, Cambridge, MA 02139, USA and Laboratory for Cryptologic Algorithms, Station 14,  ´Ecole Polytechnique F ´ed ´erale de Lausanne, 1015 Lausanne, Switzerland Received 20 July 2007 and revised 25 June 2009. [8] Anne Canteaut, C ´edric Lauradoux and Andr ´e Seznec, Understanding cache attacks, April 2006. [9] Johannes Blomer and Volker Krummel, Analysis of countermeasures against access driven cache attacks on AES, Faculty of Computer Science, Electrical Engineering and Mathematics University of Paderborn, Germany 2009. [10] Hamdan.O.Alanazi, B.B.Zaidan, A.A.Zaidan, Hamid A.Jalab, M.Shabbir and Y. Al-Nabhani, New Comparative Study Between DES, 3DES and AES within Nine Factors, Journal of Computing, Volume 2, Issue 3, March 2010. [11] Henri Gi lbert and Thomas Peyrin, Super-Sbox Cryptanalysis:Improved Attacks for AES-like Permutations, Orange Labs, France [12] Elisabeth Oswald, Stefan Mangard, Norbert Pramstaller and Vincent Rijmen, Institute for Applied Information Processing and Communciations (IAIK), Austria, 2005. [13] Kai Schramm, Gregor Leander, Patrick Felke and Christof Paar, A Collision-Attack on AES Combining Side Channel and Differential Attack, Horst Gortz Institute for IT Security, Germany 2005. [14] Alex Biryukov and Dmitry Khovratovich, Related-Key Cryptanalysis of the Full AES-192 and AES-256, University of Luxembourg 2011. [15] A Chosen-Plaintext Linear Attack on DES, Lars R. Knudsen and John Erik Mathiassen Department of Informatics, University of Bergen, N5020 Bergen, Norway, 2000. [16] Jawahar Thakur and Nagesh Kumar, DES, AES and Blowfish: Symmetric Key Cryptography, Algorithms Simulation Based Performance Analysis, International Journal of Emerging Technology and Advanced Engineering Website: www.ije tae.com (ISSN 2250-2459, Volume 1, Issue 2, December 2011) [17] Stefan Tillich and Christoph Herbst, Attacking State-of-the-Art Software Countermeasures A Case Study for AES, Institute for Applied Information Processing and Communications, Inffeldgasse 16a, A-8010 Graz, Austria

Vinegar :: essays research papers fc

Vinegar Chris Nacey Writing 101 Final draft 2-19-1997 When I was a child, I spent a lot of time in the kitchen with my mother. She liked to cook and so did I. Because of this, I learned my way around the kitchen. I knew the place for everything, and I knew the uses of most everything. There was only one paradox, in my knowledge of the kitchen: vinegar. My mother had one bottle of vinegar for as long as I can remember. She never used it in cooking, or taught me how to for that matter. Our bottle of White Wine Vinegar sat in our cupboard: on the bottom shelf, enigmatically, untouched, detached. I knew that my mother wouldn't have it without reason. It was in the kitchen, so I concluded that it must be some sort of, rarely used, cooking staple. I would never have guessed then that vinegar had so many uses. Just the other day, I was in the mall visiting a friend that works at Frankincense and Myrrh. While there, I happened upon some bottles that caught my eye. They were attractive looking ornamental bottles. Each one was filled with mysterious, colored liquids: the colors varied from red to brown to yellow. In the liquids were berries', sprigs of herbs, and things of the such. I thought they looked interesting, so I picked up a bottle that I recognized as having sage in it. I took a look at the label. On the label were listed the ingredients: sage, rosemary, and southernwood leaves. When I read the front of the bottle, I was surprised to find that I was looking at an herbal vinegar hair rinse. Before this I never knew that such a thing existed. After my experience at the mall, I became aware that vinegar didn't just belong in the kitchen. This intrigued me. I decided to find out more about vinegar and its uses. Nobody knows the exact origins of vinegar, but there are many stories and beliefs surrounding this strange liquid.(Oster 3) The Roman Army was recorded to have mixed vinegar with water to make a sort of Gatorade for the soldiers. In the eighteenth and nineteenth century United States, similar drinks known as "shrubs" or "switchels" were made by field laborers. To make these drinks, they mixed either fruit juices or water, with sometimes salt, and fruit-flavored vinegars.(Oster 4) The earliest recorded use of vinegar, however, was in Babylonia around 5,000 B.C. There, it was typically made from dates, and commonplace as a medicine.(Oster 3) Throughout history, vinegar has been used medicinally.

Euclid :: essays research papers

Little is know about Euclid, the father of geometry. Records show that he lived somewhere around 300 B.C. He was a Greek mathematician and is probably best known for his work Elements. Since little is known about the personal life of Euclid, it is difficult to do a biography on him.   Ã‚  Ã‚  Ã‚  Ã‚  His chief work, entitled Elements, is a comprehensive essay on mathematics. It includes 13 volumes that entail such subjects as plane geometry, dealing with the properties of flat surfaces and of planar figures, such as the triangle; proportion in general, a particular kind of relation between groups of numbers or quantities; the properties of numbers; incommensurable magnitudes; and solid geometry, branch of geometry that deals with the properties and measurement of geometric figures in three-dimensional space. Some people say that the geometrical sections of Elements were actually rearrangements of Exodus previous work. However Euclid himself is said to have made several discoveries in his Number Theory, which is a branch of mathematics that deals with the properties and relationships of numbers.   Ã‚  Ã‚  Ã‚  Ã‚  Most historians believe Euclid was educated at Athens. His teachers may have included pupils of Plato, who was a philosopher and one of the most influential thinkers in Western philosophy. Euclid thought geometry in Alexandria and opened a school of mathematics there. He also wrote Data, which was a collection of geometrical theorems; Phenomena, a description of the heavens; and The Division of the Scale, which is a mathematical discussion of music. But yet again many historians believe many of these works (other than the Elements) were spuriously credited to him, others disagree and say that indeed his works are that of his own. Euclid's Elements was used as a text for 2000 years, and even today a modified version of its first few books forms the basis of high school instruction in plane geometry.

Free Flow of Capital in Developing Countries Essay -- Essays Papers

Free Flow of Capital in Developing Countries Today, there are very few who argue against free trade, however, the idea of capital mobility to and from developing countries is a highly debated issue. Capital is the financing(money) or goods, used to produce other goods. Capital can further be split among capital debt and capital equity/finance. Equity capital or financing, is money raised by a business in exchange for a share of ownership. Ownership is achieved through shares of stock. Debt capital is represented by funds borrowed by a business that must be repaid over a period of time, usually with interest. Typically, short term debt is of less concern because if stockholders sell out, the value of the stock falls and the stockholder is hurt. The company isn’t necessarily hurt now, but will have a difficult time raising funds through future stock issues. Debt is of more concern. If short term debt isn’t renewed, than the company has to liquidate assets in order to pay. Therefore, capital mobility is the free flow of liquid investments from one country to another. Now although capital mobility could finance the world’s developing countries, increase wages, and create a more competitive world market (which is very beneficial to consumers); there are negative affects including income inequality, corruption, and bad capital control management . This paper will tackle both the good and bad aspects of capital flows in order to further analyze the theory of capital mobility. Before continuing it is necessary to look at some of the background and purpose of capital flows. Only until around 1980, have developing countries seen this idea as positive. Before, there was the feeling that with foreign capital a... ...s should absolutely approach with caution, because capital flows are too unstable to gamble with. Resources - Class Lecture Notes: â€Å"Trade and Capital Flows† - Class Handout: â€Å"Trade and Employment† - Hartwell, A. Christopher. Policy Analysis: The Case Against Capital Controls. The CATO Institute. Washington D.C. June 14, 2001. - http://econ.cudenver.edu/beckman/econ4410/stiglitz-world%20crisis.doc - http://quote.bloomberg.com/apps/news pid=10000039&sid=aFNcMq9i7rx0&refer= columnist_derosa - http://www.bepress.com/ev/vol1/iss1/art1/ - http://0-firstsearch.oclc.org.skyline.cudenver.edu/WebZ/FSFETCH?fetchtype=full record:sessionid=sp07sw02-58421-e0iyjwrgp5q5z:entitypagenum=3:0:recno=1 :resultset=1:format=FI:next=html/record.html:bad=error/badfetch.html:entitytop recno=1:entitycurrecno=1:numrecs=1

Essqy

The perks of being a wallflower The Perks of being a wallflower by Stephen Chbosky is about a boy named Charlie he finds a group of friends sort of like him, who became his friends and introduced him into experience common to many teens. His new group of friends gives Charlie something precious he has never had before: a sense of belonging because he is a lonely teen. For example, Charlie is lonely when he is at home â€Å"it has been very lonely because my sister is busy being the oldest one in our family. My brother is busy being a football player at pen state† (pg 8).He clearly wants to spend time with his family because he loves them. He doesn’t want to be alone. Charlie speaks about his life and says â€Å"so, this is my life and I want you to know that Im both happy and sad and Im trying to figure out how out how that could be† (pg 2). There are certain things that make him sad and happy he wants to know what those things are but Cant. â€Å"In the silence , I remembered this one time that I never told anybody about the time we were walking. Just the three of us. And I was in the middle†¦I just remember walking between them feeling for the first time that I belonged some where† (pg 198).When Charlie is alone he was thinking about how lonely he was and how he felt that he mattered and wasn’t a lone. I think Stephen Chbosky did a good job showing all the emotions and feelings Charlie had because a lot of people and relate to how he is feeling. According to the mental health foundation research shows that one in then people often feel lonely (11%) and half think that people are getting lonelier in general (48%) the report says the way people now live is impacting on their ability to connect with others.More people live alone: The percentage of households occupied by one person doubled from 64% in 1972 to 12% in 2008. (1) In recent years, social psychologist has expressed concern about the friendless male. Many studies h ave concluded that women have better relational skills which help them to be more successful at making and keeping friends. Women on the other hand, are more likely than men to express their emotions and display empathy and compassion in response to the emotions of others. (2) The effects of depression, suicide, drug addiction, alcohol addiction and acute and chronic illness. 3) Many people who are lonely can get help from doing research or going to a professional doctor who can help them they can also try to socialize with family or friends. The Perks of Being a Wallflower shows a boy who deals with loneliness and how he tries to make friends. Feeling alone is bad for your health and if you feel alone you should talk to someone about it and get help. Sources: 1) http://m. ivy-rose. co. uk/Articles/modern-life-leading-to-loneliness 2) http://www. leaderu. com/orgs/probe/docs/lonely. html 3) http://www. psychologistanywhereanytime. com/realationships_psychologist/psychologist_lonelin ess. htm