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129-717: The project consists of the satellite Micius , or Mozi ( Chinese : 墨子 ), after the ancient Chinese philosopher, operated by the Chinese Academy of Sciences , as well as ground stations in China. The University of Vienna and the Austrian Academy of Sciences are running the satellite's European receiving stations. The satellite conducted Space-Earth quantum key distribution ( Chinese : 量子密钥分发 ) experiments, facilitated by laser communications experiment carried on Tiangong-2 space laboratory module. QUESS

258-520: A star network topology, this is less of a problem. The key material must be securely disposed of after use, to ensure the key material is never reused and to protect the messages sent. Because the key material must be transported from one endpoint to another, and persist until the message is sent or received, it can be more vulnerable to forensic recovery than the transient plaintext it protects (because of possible data remanence). As traditionally used, one-time pads provide no message authentication ,

387-573: A Mohist in a debate with Mencius (in the Mengzi ), where the Mohist argued, in relation to carrying out universal love, that "we begin with what is near." Also, in the first chapter in the Mozi on the topic of universal love, Mozi argued that the best way of being filial to one's parents is to be filial to the parents of others. The foundational principle was therefore that benevolence, as well as malevolence,

516-638: A commercial one-time tape system. Each country prepared the keying tapes used to encode its messages and delivered them via their embassy in the other country. A unique advantage of the OTP in this case was that neither country had to reveal more sensitive encryption methods to the other. U.S. Army Special Forces used one-time pads in Vietnam. By using Morse code with one-time pads and continuous wave radio transmission (the carrier for Morse code), they achieved both secrecy and reliable communications. Starting in 1988,

645-432: A computationally unbounded attacker's likelihood of successful forgery is less than p ), but this uses additional random data from the pad, and some of these techniques remove the possibility of implementing the system without a computer. Due to its relative simplicity of implementation, and due to its promise of perfect secrecy, one-time-pad enjoys high popularity among students learning about cryptography, especially as it

774-519: A general attitude of care towards others. However, this does not require that we renounce all forms of special relationships we have with our families and friends. In fact, the Mohists introduce the problem that universal love is meant to solve by lamenting the fact that fathers and sons don't care for each other, and so must instead adopt an attitude of universal love. Conversely, the Mohists hope, when people adopt an attitude of universal love, society as

903-481: A global network by 2030. The mission cost was around US$ 100 million in total. The initial experiment demonstrated quantum key distribution (QKD) between Xinjiang Astronomical Observatory near Ürümqi and Xinglong Observatory near Beijing – a great-circle distance of approximately 2,500 kilometres (1,600 mi). In addition, QUESS tested Bell's inequality at a distance of 1,200 km (750 mi) – further than any experiment to date – and teleported

1032-649: A life of asceticism and self-restraint, renouncing both material and spiritual extravagance. Like Confucius, Mozi idealized the Xia dynasty and the ancients of Chinese mythology , but he also criticized the Confucian belief that modern life should be patterned on the ways of the ancients. Mozi argued that what is thought of as "ancient" was actually innovative in its time, and thus should not be used to hinder present-day innovation . Though Mozi did not believe that history necessarily progresses, as did Han Fei Zi , he shared

1161-422: A morally consistent universe. Heaven, it is argued, is the ultimate moral standard, while ghosts and spirits serve as Heaven's enforcers. Both doctrines, when adopted, promote societal benefit both by enabling people to rely upon an objective standard to guide their actions (namely, Heaven), and by acting as a sort of cosmic authority capable of enacting rewards and punishments. Mozi's condemnation of music rests on

1290-422: A notion that philosophers in other schools found absurd, as they interpreted this notion as implying no special amount of care or duty towards one's parents and family. Overlooked by those critics, however, was a passage in the chapter on "Self-Cultivation" which stated, "When people near-by are not befriended, there is no use endeavoring to attract those at a distance." This point was also precisely articulated by

1419-514: A one-time pad of letters to encode plaintext directly as in the example below. Leo Marks describes inventing such a system for the British Special Operations Executive during World War II , though he suspected at the time that it was already known in the highly compartmentalized world of cryptography, as for instance at Bletchley Park . The final discovery was made by information theorist Claude Shannon in

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1548-586: A philosophy emphasizing universal love, social order , the will of Heaven , sharing, and honoring the worthy. Mohism was actively developed and practiced across Warring States–era China, but fell out of favor following the establishment of the Qin dynasty in 221 BCE. While tradition assumes the destruction of many Mohist texts in 213 BCE as part of Emperor Qin Shi Huang 's burning of books and burying of scholars , traces of Mohism can still be seen late in

1677-541: A photon state between Shiquanhe Observatory in Ali , Tibet Autonomous Region , and the satellite. This requires very accurate orbital maneuvering and satellite tracking so the base stations can keep line-of-sight with the craft. In 2021 full quantum state teleportation was demonstrated over 1,200 km (750 mi) at ground, based on entanglement distributed by the satellite. Once experiments within China concluded, QUESS created an international QKD channel between China and

1806-428: A powerful enough quantum computer. One-time pads, however, would remain secure, as perfect secrecy does not depend on assumptions about the computational resources of an attacker. Despite Shannon's proof of its security, the one-time pad has serious drawbacks in practice because it requires: One-time pads solve few current practical problems in cryptography. High-quality ciphers are widely available and their security

1935-602: A profound influence on the development of classical Chinese philosophy in general. In fact, Mohism was so prominent during the Warring States period that philosophical opponents, including Mencius and some authors of the Daoist anthology, the Zhuangzi , lament the very prevalence and widespread influence of their ideas. In modern times, Mohism has been given a fresh analysis. Sun Yat-Sen used "universal love" as one of

2064-544: A quantum analogue of the one time pad, which can be used to exchange quantum states along a one-way quantum channel with perfect secrecy, which is sometimes used in quantum computing. It can be shown that a shared secret of at least 2n classical bits is required to exchange an n-qubit quantum state along a one-way quantum channel (by analogue with the result that a key of n bits is required to exchange an n bit message with perfect secrecy). A scheme proposed in 2000 achieves this bound. One way to implement this quantum one-time pad

2193-416: A quantum setting. Suppose Alice wishes to send the message hello to Bob . Assume two pads of paper containing identical random sequences of letters were somehow previously produced and securely issued to both. Alice chooses the appropriate unused page from the pad. The way to do this is normally arranged for in advance, as for instance "use the 12th sheet on 1 May", or "use the next available sheet for

2322-452: A random secret key (also referred to as a one-time pad ). Then, each bit or character of the plaintext is encrypted by combining it with the corresponding bit or character from the pad using modular addition . The resulting ciphertext will be impossible to decrypt or break if the following four conditions are met: It has also been mathematically proven that any cipher with the property of perfect secrecy must use keys with effectively

2451-497: A random secret key transmitted using pairs of entangled photons sent with random polarization , with each party receiving one-half of the pair. This secret key can then be used as a one-time pad , allowing the two parties to communicate securely through normal channels. Any attempt to eavesdrop on the key will disturb the entangled state in a detectable way. QKD has been attempted on Earth, both with direct line-of-sight between two observatories, and using fibre optic cables to transmit

2580-407: A result, society will suffer, and so the doctrine that there is fate ought to be rejected. "Mozi" is also the name of the philosophical anthology written and compiled by followers of Mozi. The text was formed by an accretional process that took place over a period of hundreds of years, beginning perhaps during or shortly after Mozi's lifetime, and lasting until perhaps the early Han dynasty. During

2709-399: A serial number and eight lines. Each line had six 5-digit numbers. A page would be used as a work sheet to encode a message and then destroyed. The serial number of the page would be sent with the encoded message. The recipient would reverse the procedure and then destroy his copy of the page. The German foreign office put this system into operation by 1923. A separate notion was the use of

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2838-439: A shared secret key to be agreed upon with relatively few messages exchanged and relatively low computational overhead. At a high level, the schemes work by taking advantage of the destructive way quantum states are measured to exchange a secret and detect tampering. In the original BB84 paper, it was proven that the one-time pad, with keys distributed via QKD, is a perfectly secure encryption scheme. However, this result depends on

2967-402: A sharp pencil, and some mental arithmetic . The method can be implemented now as a software program, using data files as input (plaintext), output (ciphertext) and key material (the required random sequence). The exclusive or (XOR) operation is often used to combine the plaintext and the key elements, and is especially attractive on computers since it is usually a native machine instruction and

3096-420: A technique for generating pure randomness is measuring radioactive emissions . In particular, one-time use is absolutely necessary. For example, if p 1 {\displaystyle p_{1}} and p 2 {\displaystyle p_{2}} represent two distinct plaintext messages and they are each encrypted by a common key k {\displaystyle k} , then

3225-497: A very large one-time-pad from place to place in a non-suspicious way, but the need to transport the pad physically is a burden compared to the key negotiation protocols of a modern public-key cryptosystem. Such media cannot reliably be erased securely by any means short of physical destruction (e.g., incineration). A 4.7 GB DVD-R full of one-time-pad data, if shredded into particles 1 mm (0.0016 sq in) in size, leaves over 4 megabits of data on each particle. In addition,

3354-477: A whole will benefit. Dovetailing with this idea is that of condemning aggression. The main targets of this doctrine are undoubtedly the rulers of the various warring states in China, who regularly embarked on expansionist military campaigns in order to increase their territory, power, and influence. However, such campaigns were enormously taxing on the population, disrupting regular farming cycles by conscripting able-bodied people for these military ends. Additionally,

3483-730: Is a proof-of-concept mission designed to facilitate quantum optics experiments over long distances to allow the development of quantum encryption and quantum teleportation technology. Quantum encryption uses the principle of entanglement to facilitate communication that can absolutely detect whether a third party has intercepted a message in transit thus denying undetected decryption . By producing pairs of entangled photons , QUESS will allow ground stations separated by many thousands of kilometres to establish secure quantum channels . QUESS itself has limited communication capabilities: it needs line-of-sight , and can only operate when not in sunlight. Further Micius satellites were planned, including

3612-469: Is also famous for his ideas about frugality, such as those concerning moderating expenses and eliminating wasteful ceremonies including music and funerals. A common misconception is that the Mohists eschewed all forms of art, but of course the Mohists' targets are more specifically elaborate, state-sponsored rituals that would place incredible financial burdens upon a mostly peasant population. This can be seen from Xunzi's own arguments against Mozi in book 10 of

3741-427: Is an example of post-quantum cryptography, because perfect secrecy is a definition of security that does not depend on the computational resources of the adversary. Consequently, an adversary with a quantum computer would still not be able to gain any more information about a message encrypted with a one time pad than an adversary with just a classical computer. One-time pads have been used in special circumstances since

3870-435: Is by dividing the 2n bit key into n pairs of bits. To encrypt the state, for each pair of bits i in the key, one would apply an X gate to qubit i of the state if and only if the first bit of the pair is 1, and apply a Z gate to qubit i of the state if and only if the second bit of the pair is 1. Decryption involves applying this transformation again, since X and Z are their own inverses. This can be shown to be perfectly secret in

3999-561: Is cancelled, stay home". The attacker's knowledge of the one-time pad is limited to this byte length, which must be maintained for any other content of the message to remain valid. This is different from malleability where the plaintext is not necessarily known. Without knowing the message, the attacker can also flip bits in a message sent with a one-time pad, without the recipient being able to detect it. Because of their similarities, attacks on one-time pads are similar to attacks on stream ciphers . Standard techniques to prevent this, such as

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4128-502: Is considered a form of consequentialism , according to which the morality of an action, statement, teaching, policy, judgment, and so on, is determined by the consequences that it brings about. In particular, Mozi thought that actions should be measured by the way they contribute to the benefit of all members of society. With this criterion, Mozi denounced things as diverse as offensive warfare, expensive funerals, and even music and dance, which he saw as serving no useful purpose. According to

4257-727: Is not currently considered a major worry. Such ciphers are almost always easier to employ than one-time pads because the amount of key material that must be properly and securely generated, distributed and stored is far smaller. Additionally, public key cryptography overcomes the problem of key distribution. High-quality random numbers are difficult to generate. The random number generation functions in most programming language libraries are not suitable for cryptographic use. Even those generators that are suitable for normal cryptographic use, including /dev/random and many hardware random number generators , may make some use of cryptographic functions whose security has not been proven. An example of

4386-514: Is often the first algorithm to be presented and implemented during a course. Such "first" implementations often break the requirements for information theoretical security in one or more ways: Despite its problems, the one-time-pad retains some practical interest. In some hypothetical espionage situations, the one-time pad might be useful because encryption and decryption can be computed by hand with only pencil and paper. Nearly all other high quality ciphers are entirely impractical without computers. In

4515-791: Is requited, and that one would be treated by others as one treats others. Mozi quoted a popular passage from the Book of Odes to bring home this point: "When one throws to me a peach, I return to him a plum." One's parents will be treated by others as one treats the parents of others. Mozi also differentiated between "intention" and "actuality", thereby placing a central importance on the will to love, even though in practice it might very well be impossible to bring benefit to everyone. In addition, Mozi argued that benevolence comes to human beings "as naturally as fire turns upward or water turns downward", provided that persons in positions of authority illustrate benevolence in their own lives. In differentiating between

4644-420: Is some ambiguity to the term "Vernam cipher" because some sources use "Vernam cipher" and "one-time pad" synonymously, while others refer to any additive stream cipher as a "Vernam cipher", including those based on a cryptographically secure pseudorandom number generator (CSPRNG). Frank Miller in 1882 was the first to describe the one-time pad system for securing telegraphy. The next one-time pad system

4773-513: Is some debate over how to understand the consequences Mozi seems most concerned with, and therefore over which kind of consequentialism to ascribe to him. Some believe the best descriptor to be state consequentialism. According to this reading, Mohist ethics makes moral evaluations based on how well the action, statement, etc., in question contributes to the stability of a state. Such state-related goods include social order, material wealth, and population growth. By centering his ethical theory around

4902-652: Is the Way of Heaven", since "Heaven nourishes and sustains all life without regard to status." Mozi's ideal of government, which advocated a meritocracy based on talent rather than background, also followed his idea of Heaven. Mozi opposed the Confucian idea of "Destiny", promoting instead an idea of "anti-fatalism" ( 非命 ). Where the Confucian philosophy held that a person's life, death, wealth, poverty, and social status were entirely dependent upon destiny and therefore could not be changed, Mozi argued that hard work and virtuous acts could change one's position in life. Mohist ethics

5031-402: Is the first to describe the physical principle behind the camera , also known as the camera obscura . One-time pad In cryptography , the one-time pad ( OTP ) is an encryption technique that cannot be cracked , but requires the use of a single-use pre-shared key that is larger than or equal to the size of the message being sent. In this technique, a plaintext is paired with

5160-421: Is the same as the a posteriori probability of a plaintext message M given the corresponding ciphertext. Conventional symmetric encryption algorithms use complex patterns of substitution and transpositions . For the best of these currently in use, it is not known whether there can be a cryptanalytic procedure that can efficiently reverse (or even partially reverse ) these transformations without knowing

5289-526: Is therefore very fast. It is, however, difficult to ensure that the key material is actually random, is used only once, never becomes known to the opposition, and is completely destroyed after use. The auxiliary parts of a software one-time pad implementation present real challenges: secure handling/transmission of plaintext, truly random keys, and one-time-only use of the key. To continue the example from above, suppose Eve intercepts Alice's ciphertext: EQNVZ . If Eve tried every possible key, she would find that

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5418-484: Is typically associated with the one-time pad because it provides a way of distributing a long shared secret key securely and efficiently (assuming the existence of practical quantum networking hardware). A QKD algorithm uses properties of quantum mechanical systems to let two parties agree on a shared, uniformly random string. Algorithms for QKD, such as BB84 , are also able to determine whether an adversarial party has been attempting to intercept key material, and allow for

5547-525: The New York Times noted that quantum technology was a focus of the thirteenth five-year plan , which the China government set out earlier that year. The Wall Street Journal said that the launch put China ahead of rivals, and brought them closer to "hack-proof communications". Several outlets identified Edward Snowden 's leak of US surveillance documents as an impetus for the development of QUESS, with Popular Science calling it "a satellite for

5676-725: The Stanford Encyclopedia of Philosophy , Mohist consequentialism, dating back to the 5th century BCE, is the "world's earliest form of consequentialism, a remarkably sophisticated version based on a plurality of intrinsic goods taken as constitutive of human welfare". Consequentialist theories vary over exactly which consequences are relevant, though they all share the same basic outcome-based structure. With Mozi's overwhelming focus on "benefit" ( 利 , li ) among other ends, and his explicit focus on making moral evaluations in light of them, Mozi's ethics indeed shares this consequentalist structure. For interpreting Mozi, however, there

5805-509: The African National Congress (ANC) used disk-based one-time pads as part of a secure communication system between ANC leaders outside South Africa and in-country operatives as part of Operation Vula, a successful effort to build a resistance network inside South Africa. Random numbers on the disk were erased after use. A Belgian flight attendant acted as courier to bring in the pad disks. A regular resupply of new disks

5934-578: The Institute for Quantum Optics and Quantum Information , Vienna, Austria − a ground distance of 7,500 km (4,700 mi), enabling the first intercontinental secure quantum video call in 2016. The launch was initially scheduled for July 2016, but was rescheduled to August, with notification of the launch being sent just a few days in advance. The spacecraft was launched by a Long March 2D rocket from Jiuquan Launch Pad 603, Launch Area 4 on 17 August 2016, at 17:40 UTC (01:40 local time). The launch

6063-517: The Lunyu ( Analects ) and Mengzi respectively, wherein the thinkers in question are portrayed as expressing emotions, chiding students, and even making mistakes. (Consider Mengzi's disastrous advice to the King of Qi to invade the state of Yan.) To contrast, Mozi has little if any personality in the text, instead serving only as a mouthpiece for Mohist philosophy. Mohism, like other schools of thought at

6192-634: The National University of Singapore and the University of Strathclyde . A German consortium has performed quantum measurements of optical signals from the geostationary Alphasat Laser Communication Terminal . The US Defense Advanced Research Projects Agency (DARPA) launched the Quiness macroscopic quantum communications project to catalyze the development of an end-to-end global quantum internet in 2012. In 2024, ESA intends to launch

6321-536: The School of Names . Mozi tried to replace what he considered to be the long-entrenched Chinese ideal of strong attachments to family and clan structures with the concept of "impartial caring" or "universal love" ( 兼愛 , jiān ài ). He argued directly against Confucians, who had philosophized that it was natural and correct for people to care about different people in different degrees. Mozi, in contrast, argued that people in principle should care for all people equally,

6450-524: The Venona project . Because the pad, like all shared secrets , must be passed and kept secure, and the pad has to be at least as long as the message, there is often no point in using a one-time pad, as one can simply send the plain text instead of the pad (as both can be the same size and have to be sent securely). However, once a very long pad has been securely sent (e.g., a computer disk full of random data), it can be used for numerous future messages, until

6579-458: The Vigenère cipher . The numerical values of corresponding message and key letters are added together, modulo 26. So, if key material begins with XMCKL and the message is hello , then the coding would be done as follows: If a number is larger than 25, then the remainder after subtraction of 26 is taken in modular arithmetic fashion. This simply means that if the computations "go past" Z,

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6708-571: The Warring States period ( c.  475  – 221 BCE). Alongside Confucianism , Mohism became the most prominent, organized schools of the Hundred Schools of Thought throughout the period. The Mozi is an anthology of writings traditionally attributed to Mozi and to his followers. Born in what is now Tengzhou , Shandong, Mozi and his followers argued strongly against both Confucianism and Taoism , with

6837-450: The XOR of the two plaintexts p 1 ⊕ p 2 {\displaystyle p_{1}\oplus p_{2}} . (This is because taking the XOR of the common key k {\displaystyle k} with itself yields a constant bitstream of zeros.) p 1 ⊕ p 2 {\displaystyle p_{1}\oplus p_{2}} is then

6966-489: The XOR operation used for the encryption of a one-time pad. Derived from his Vernam cipher , the system was a cipher that combined a message with a key read from a punched tape . In its original form, Vernam's system was vulnerable because the key tape was a loop, which was reused whenever the loop made a full cycle. One-time use came later, when Joseph Mauborgne recognized that if the key tape were totally random, then cryptanalysis would be impossible. The "pad" part of

7095-540: The Xunzi "Enriching the State," where Xunzi argues against Mozi that prominent displays of wealth on the part of the state is necessary to maintaining social order. Some modern-day supporters for Mozi (as well as Communism) make the claim that Mohism and modern Communism share a lot in terms of ideals for community life. Others would claim that Mohism shares more with the central ideas of Christianity , especially in terms of

7224-429: The 1940s who recognized and proved the theoretical significance of the one-time pad system. Shannon delivered his results in a classified report in 1945 and published them openly in 1949. At the same time, Soviet information theorist Vladimir Kotelnikov had independently proved the absolute security of the one-time pad; his results were delivered in 1941 in a report that apparently remains classified. There also exists

7353-674: The Eagle-1 quantum key distribution satellite, with a goal similar to that of the Chinese QUESS. It will be part of the development and deployment of the European Quantum Communication Infrastructure (EuroQCI). Mozi Mozi , personal name Mo Di , was a Chinese philosopher , logician, and founder of the Mohist school of thought, making him one of the most important figures of

7482-569: The Han dynasty, as Confucianism came to be the official school of political thought, Mohism gradually lost both its adherents and influence while simultaneously being partly incorporated into more mainstream political thought. The text was eventually neglected, and only 58 of the text's original 71 books ( pian ) survive, some of which, notably the later Mohist Canons , contain significant textual corruptions and are fragmentary in nature. The anthology can be divided into 5 main groups, which are determined on

7611-457: The QKD scheme being implemented correctly in practice. Attacks on real-world QKD systems exist. For instance, many systems do not send a single photon (or other object in the desired quantum state) per bit of the key because of practical limitations, and an attacker could intercept and measure some of the photons associated with a message, gaining information about the key (i.e. leaking information about

7740-572: The State of Lu. He taught that the defense of a city did not depend only on fortification, weaponry, and food supply, but rather that it was also important to keep talented people close by and to put trust in them. Mozi's moral teachings emphasized introspection , self-reflection , and authenticity , rather than obedience to rituals . He observed that people often learned about the world through adversity. By reflecting on one's own successes and failures, one attains true self-knowledge rather than mere conformity to ritual. Mozi exhorted people to lead

7869-431: The basic normative attitude the Mohists encourage us to adopt towards others. The idea is that people ought to consider all others as being part of their scope of moral concern. Indeed this is perhaps the most infamous of Mohist doctrines, and was criticized early on by philosophers such as Mengzi, who held that the doctrine was akin to renouncing one's family. However, close readings of the texts by modern scholars have shown

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7998-553: The basis of both chronological and thematic features: The Mozi is a rich source of insight into early Chinese dynastic history, culture, and philosophy. The text frequently cites ancient classics, such as the Shang Shu , and at times departs from the received version, giving scholars insight into the textual development of such classics as well. The texts portray Mozi as a mouthpiece for Mohist philosophy and not much else. This picture contrasts that of Confucius and Mencius found in

8127-425: The body. While xing refers to the flesh-bloody part of human being, the concept of xin focuses on the aspect of cognition and is closely related to the concept of shan ( 善 , 'goodness'), ai ( 愛 , 'love'), zhi ( 志 , 'will') and xing. Some views claim that Mozi's philosophy was at once more advanced and less so than that of Confucius. Indeed the Mohists were radical political reformers who sought primarily to benefit

8256-401: The demands of Mohist universal love to be much more mild and reasonable. Additionally, given the accretional nature of the texts, the audience of such texts may have changed depending upon the Mohists' social influence, and so the demands for universal love made on rulers, for example, is considerably higher than that made on the masses. At its most basic, however, the doctrine merely encourages

8385-743: The early 1900s. In 1923, they were employed for diplomatic communications by the German diplomatic establishment. The Weimar Republic Diplomatic Service began using the method in about 1920. The breaking of poor Soviet cryptography by the British , with messages made public for political reasons in two instances in the 1920s ( ARCOS case ), appear to have caused the Soviet Union to adopt one-time pads for some purposes by around 1930. KGB spies are also known to have used pencil and paper one-time pads more recently. Examples include Colonel Rudolf Abel , who

8514-576: The early Han (from 202 BCE), in syncretic texts like the Huainanzi of c.  139 BCE . As Confucianism became the dominant school of thought during the Han dynasty (202 BCE – 220 CE), Mohism disappeared almost entirely by the middle of the Western Han period of 202 BCE to 9 CE. Mozi is referenced in the 6th-century CE Thousand Character Classic , which records that he

8643-699: The encrypted message (i.e., the ciphertext ) provides no information about the original message to a cryptanalyst (except the maximum possible length of the message). This is a very strong notion of security first developed during WWII by Claude Shannon and proved, mathematically, to be true for the one-time pad by Shannon at about the same time. His result was published in the Bell System Technical Journal in 1949. If properly used, one-time pads are secure in this sense even against adversaries with infinite computational power. Shannon proved, using information theoretic considerations, that

8772-445: The equivalent of a running key cipher. If both plaintexts are in a natural language (e.g., English or Russian), each stands a very high chance of being recovered by heuristic cryptanalysis, with possibly a few ambiguities. Of course, a longer message can only be broken for the portion that overlaps a shorter message, plus perhaps a little more by completing a word or phrase. The most famous exploit of this vulnerability occurred with

8901-491: The fact that officials tended to indulge in them at the expense of their duties. Finally, the Mohists rejected the idea of fatalism, or the idea that there is fate. The Mohists reject this idea on the grounds that it encourages lazy and irresponsible behavior. When people believe that there is fate, and that the consequences of their actions lie beyond their control, people will not be encouraged to improve themselves, nor will they be willing to take responsibility for disasters. As

9030-583: The fair distribution of wealth, yet he recognized the need for strong urban defenses so he could maintain the harmonious society he desired. The "material wealth" of Mohist consequentialism refers to basic needs like shelter and clothing, and the "order" of Mohist consequentialism refers to Mozi's stance against warfare and violence, which he viewed as pointless and a threat to social stability. Stanford sinologist David Shepherd Nivison , in The Cambridge History of Ancient China , writes that

9159-429: The form of 10 core doctrines: Each of these doctrines is justified on the grounds that it produces the best consequences for society, and that all people stand to benefit from adopting them. Promoting the worthy, for example, encourages people in positions of power to hire competent and worthy subordinates to fill posts, rather than hire friends and relatives instead. The reasoning here is that someone better qualified for

9288-542: The foundations for his idea of Chinese democracy. More recently, Chinese scholars under Communism have tried to rehabilitate Mozi as a "philosopher of the people", highlighting his rational-empirical approach to the world as well as his "proletarian" background. The body in the Mozi is constructed by xing ( 形 , 'body'), xin ( 心 , 'heart'), qi ( 氣 , 'energy') 'which is in accord with the Pre-Qin thinkers' understanding to

9417-734: The greatest hero to come from Henan . His passion was said to be for the good of the people, without concern for personal gain or even for his own life or death. His tireless contribution to society was praised by many, including Confucius's disciple Mencius . Mencius wrote in Jinxin ( Chinese : 孟子盡心 ; pinyin : Mengzi jinxin ) that Mozi believed in love for all mankind, noting that, as long as something benefitted mankind, Mozi would pursue it even if it meant "hurting his head or his feet". Zhang Tai Yan said that, in terms of moral virtue, even Confucius and Laozi could not compare to Mozi. Mozi travelled from one crisis zone to another throughout

9546-690: The idea of "universal love" (in Greek, " agape "), the " Golden Rule ", and the relation of humanity to the supernatural realm. However, Mohism is undoubtedly a product of Warring States China, a period of tremendous political violence and turmoil. The Mohists were political reformers, but they did not seek to challenge the monarchical model of government that prevailed during that time, and sought instead to reform from within by encouraging governments to hire competent people to carry out political tasks, care for their people inclusively, eliminate frivolous government spending, and halt all wars of aggression. In many ways

9675-417: The ideas of "universal" ( jian ) and "differential" ( bie ), Mozi said that "universal" originated from righteousness while "differential" entailed human effort. Mozi also held a belief in the power of ghosts and spirits, although he is often thought to have only worshipped them pragmatically. In fact, in his discussion on ghosts and spirits, he remarked that, even if they did not exist, communal gatherings for

9804-568: The influence of Mohism was a victim of its own successes, and it is fairly easy to understand its decline. The Mohists' ideas about the importance of meritocracy and universal love were gradually absorbed by mainstream Confucian thinking. Their opposition to offensive warfare became irrelevant once the various Warring States were unified under the Qin and later Han dynasty, and their religious superstitions were eventually replaced with less supernatural accounts. So their most promising ideas were metabolized by

9933-443: The job will perform better and enable society as a whole to benefit. Identifying upward refers to the idea that people in subordinate positions in society must look to their superiors as models for their own conduct. Provided that the superiors are indeed morally competent and worthy of emulation, the rest of society will always have a reliable guide for their own actions, thereby giving rise to social benefits. Universal love refers to

10062-407: The key XMCKL would produce the plaintext hello , but she would also find that the key TQURI would produce the plaintext later , an equally plausible message: In fact, it is possible to "decrypt" out of the ciphertext any message whatsoever with the same number of characters, simply by using a different key, and there is no information in the ciphertext that will allow Eve to choose among

10191-555: The key tape could be completely random and that, if so, cryptanalysis would be more difficult. Together they invented the first one-time tape system. The next development was the paper pad system. Diplomats had long used codes and ciphers for confidentiality and to minimize telegraph costs. For the codes, words and phrases were converted to groups of numbers (typically 4 or 5 digits) using a dictionary-like codebook . For added security, secret numbers could be combined with (usually modular addition) each code group before transmission, with

10320-417: The key used during encryption. Asymmetric encryption algorithms depend on mathematical problems that are thought to be difficult to solve, such as integer factorization or the discrete logarithm . However, there is no proof that these problems are hard, and a mathematical breakthrough could make existing systems vulnerable to attack. Given perfect secrecy, in contrast to conventional symmetric encryption,

10449-411: The king that his disciples had already trained the soldiers of Song in his fortification methods, so it would be useless to kill him. The Chu king was forced to call off the war. On the way back, however, the soldiers of Song, not recognizing Mozi, would not allow him to enter their city, and he had to spend a night freezing in the rain. After this episode, he also prevented the state of Qi from attacking

10578-420: The lack of which can pose a security threat in real-world systems. For example, an attacker who knows that the message contains "meet jane and me tomorrow at three thirty pm" can derive the corresponding codes of the pad directly from the two known elements (the encrypted text and the known plaintext). The attacker can then replace that text by any other text of exactly the same length, such as "three thirty meeting

10707-467: The latter's critique of fate ( 命 , mìng ). Mozi believed that people were capable of changing their circumstances and directing their own lives, which could be achieved by applying one's senses to observing the world, as well as judging objects and events by their causes, functions, and historical bases. This was the "three-prong method" Mozi recommended for testing the truth or falsehood of statements. His students later expanded upon this theory to form

10836-405: The livelihood and productivity of the common people. Mozi managed to attract a large following during his lifetime, rivaling that of Confucius. His followers—mostly technicians and craftspeople—were organized in a disciplined order that studied both Mozi's philosophical and technical writings. According to some accounts of the popular understanding of Mozi at the time, he had been hailed by many as

10965-415: The main Mohist ideas about frugality. In one's own projects, utility ought to be the only consideration. What is the purpose of houses? It is to protect us from the wind and cold of winter, the heat and rain of summer, and to keep out robbers and thieves. Once these ends have been secured, that is all. Whatever does not contribute to these ends should be eliminated. The Mohists took particular offense to

11094-421: The main focus of Mozi's consequentialism in the welfare of the people themselves rather than that of the state as a whole. Such interpretations as Chris Fraser's argue that it is a mistake to view Mozi's focus on the collective well-being of a population as a focus on the well-being of the state itself rather than its constituents. In this way, Mozi tended to evaluate actions based on whether they provide benefit to

11223-473: The masses and challenge the practices of the ruling orthodoxy, often targeting a perceived wasteful aristocracy whom they referred to as "the gentlemen of the world." The Mohist idea of "universal love" embraced a broader idea of human community than that of the Confucians, arguing that the scope of individuals' moral concern should include all people. Opponents of this idea often claimed that "universal love"

11352-425: The message hello . Both Alice and Bob destroy the key sheet immediately after use, thus preventing reuse and an attack against the cipher. The KGB often issued its agents one-time pads printed on tiny sheets of flash paper, paper chemically converted to nitrocellulose , which burns almost instantly and leaves no ash. The classical one-time pad of espionage used actual pads of minuscule, easily concealed paper,

11481-411: The modern world, however, computers (such as those embedded in mobile phones ) are so ubiquitous that possessing a computer suitable for performing conventional encryption (for example, a phone that can run concealed cryptographic software) will usually not attract suspicion. A common use of the one-time pad in quantum cryptography is being used in association with quantum key distribution (QKD). QKD

11610-431: The moral goods of Mohism "are interrelated: more basic wealth, then more reproduction; more people, then more production and wealth ... if people have plenty, they would be good, filial, kind, and so on unproblematically". In contrast to Jeremy Bentham , Mozi did not believe that individual happiness was important; the consequences of the state outweigh the consequences of individual actions. Alternative readings locate

11739-492: The motion will never stop. This is as true as that an ox is not a horse.' which, he claims, is a precursor to Newton's first law of motion. Mozi also contains speculations in optics and mechanics that are similarly strikingly original, although their ideas were not taken up by later Chinese philosophers. The Mohist tradition is also highly unusual in Chinese thought in that it devoted time to developing principles of logic. He

11868-542: The name comes from early implementations where the key material was distributed as a pad of paper, allowing the current top sheet to be torn off and destroyed after use. For concealment the pad was sometimes so small that a powerful magnifying glass was required to use it. The KGB used pads of such size that they could fit in the palm of a hand, or in a walnut shell. To increase security, one-time pads were sometimes printed onto sheets of highly flammable nitrocellulose , so that they could easily be burned after use. There

11997-409: The next message". The material on the selected sheet is the key for this message. Each letter from the pad will be combined in a predetermined way with one letter of the message. (It is common, but not required, to assign each letter a numerical value , e.g., a is 0, b is 1, and so on.) In this example, the technique is to combine the key and the message using modular addition , not unlike

12126-408: The one-time pad has a property he termed perfect secrecy ; that is, the ciphertext C gives absolutely no additional information about the plaintext . This is because (intuitively), given a truly uniformly random key that is used only once, a ciphertext can be translated into any plaintext of the same length, and all are equally likely. Thus, the a priori probability of a plaintext message M

12255-405: The one-time pad is immune even to brute-force attacks. Trying all keys simply yields all plaintexts, all equally likely to be the actual plaintext. Even with a partially known plaintext, brute-force attacks cannot be used, since an attacker is unable to gain any information about the parts of the key needed to decrypt the rest of the message. The parts of the plaintext that are known will reveal only

12384-401: The pad), while passing along unmeasured photons corresponding to the same bit of the key. Combining QKD with a one-time pad can also loosen the requirements for key reuse. In 1982, Bennett and Brassard showed that if a QKD protocol does not detect that an adversary was trying to intercept an exchanged key, then the key can safely be reused while preserving perfect secrecy. The one-time pad

12513-570: The parts of the key corresponding to them, and they correspond on a strictly one-to-one basis ; a uniformly random key's bits will be independent . Quantum cryptography and post-quantum cryptography involve studying the impact of quantum computers on information security . Quantum computers have been shown by Peter Shor and others to be much faster at solving some problems that the security of traditional asymmetric encryption algorithms depends on. The cryptographic algorithms that depend on these problems' difficulty would be rendered obsolete with

12642-527: The people, which he measured in terms of an enlarged population (states were sparsely populated in his day), a prosperous economy, and social order. Indeed these are collective goods rather than individual ones, which is a major difference between Mohist consequentialism and modern, Western versions. However, this reading emphasizes that collective goods are better considered as aggregated individual goods rather than as state goods. This consequentialist structure supports Mohist ethics and politics, which survives in

12771-476: The photons. However, fiber optics and the atmosphere both cause scattering, which destroys the entangled state, and this limits the distance over which QKD can be carried out. Sending the keys from an orbiting satellite results in less scattering, which allows QKD to be performed over much greater distances. In addition, QUESS could test some of the basic foundations of quantum mechanics . Bell's theorem says that no local hidden-variable theory can ever reproduce

12900-408: The post-Snowden age". QUESS is the first spacecraft launched capable of generating entangled photons in space, although transmission of single photons via satellites has previously been demonstrated by reflecting photons generated at ground-based stations off orbiting satellites. While not generating fully entangled photons, correlated pairs of photons have been produced in space using a cubesat by

13029-517: The practice of extremely lavished funerals and demanding mourning rituals. Such funerals and rituals would potentially bankrupt an entire clan, at least temporarily, and disrupt its farming practices. For the dead in higher positions of authority, this disruption would affect an even greater number of people. Again, the point here is to promote benefit across society, and the Mohists believe that adopting frugal practices will do so. Mozi's ideas about ghosts and spirits follow from their religious beliefs in

13158-400: The practices is ethically wrong for the same reason that robbery and murder are wrong. In fact, according to Mozi, the two are actually one and the same; for what is an expansionist war of aggression other than robbery and murder on a grand scale? And yet, Mozi laments, those rulers who execute robbers and murderers engage in the very same practices. With respect to universal love, indeed part of

13287-487: The predictions of quantum physics, and QUESS was able to test the principle of locality over 1,200 km (750 mi). The quantum key distribution experiment won American Association for the Advancement of Science (AAAS)'s Newcomb Cleveland Prize in 2018 for its contribution to laying the foundation for ultra-secure communication networks of the future. QUESS lead scientist Pan Jianwei told Reuters that

13416-476: The project has "enormous prospects" in the defence sphere. The satellite will provide secure communications between Beijing and Ürümqi, capital of Xinjiang , the remote western region of China. The US Department of Defense believes China is aiming to achieve the capability to counter the use of enemy space technology. Chinese Communist Party general secretary Xi Jinping has prioritised China's space program, which has included anti-satellite missile tests, and

13545-487: The promotion of such state-related ends, Mozi shows himself to be a state consequentialist. Unlike hedonistic utilitarianism , which views pleasure as a moral good, "the basic goods in Mohist consequentialist thinking are ... order, material wealth, and increase in population". During Mozi's era, war and famines were common, and population growth was seen as a moral necessity for a harmonious society. Mozi opposed wars because they wasted life and resources while interfering with

13674-521: The ravaged landscape of the Warring States, trying to dissuade rulers from their plans of conquest. According to the chapter "Gongshu" in the Mozi , he once walked for ten days to the state of Chu in order to forestall an attack on the State of Song. At the Chu court, Mozi engaged in nine simulated war games with Gongshu Ban , the chief military strategist of Chu, and overturned each one of his stratagems. When Gongshu Ban threatened him with death, Mozi informed

13803-456: The reason why rulers believe it is acceptable to invade and conquer other states while it is not acceptable for their own subjects to rob and steal from one another is that the people in neighboring states are not part of the rulers' scope of moral concern. If rulers were to instead include these people and refrain from wars of aggression, all states, those attacking and those defending, will benefit. Moderation in use and moderation in burials are

13932-466: The respective ciphertexts are given by: where ⊕ {\displaystyle \oplus } means XOR . If an attacker were to have both ciphertexts c 1 {\displaystyle c_{1}} and c 2 {\displaystyle c_{2}} , then simply taking the XOR of c 1 {\displaystyle c_{1}} and c 2 {\displaystyle c_{2}} yields

14061-477: The risk of compromise during transit (for example, a pickpocket swiping, copying and replacing the pad) is likely to be much greater in practice than the likelihood of compromise for a cipher such as AES . Finally, the effort needed to manage one-time pad key material scales very badly for large networks of communicants—the number of pads required goes up as the square of the number of users freely exchanging messages. For communication between only two persons, or

14190-462: The sake of making sacrificial offering would play a role in strengthening social bonds. Furthermore, for Mozi the will of Heaven ( 天 , tiān ) was that people should love one another, and that mutual love by all would bring benefit to all. Therefore, it was in everyone's interest that they would love others "as they love themselves". According to Mozi, Heaven should be respected because failing to do so would subject one to punishment. For Mozi, Heaven

14319-458: The same economic considerations as their general ideas of frugality. In ancient China, grand musical ceremonies established by rulers would place enormous financial and human strains on populations, and so Mozi condemned such ceremonies for this reason. Mozi did not object to music in principle—"It's not that I don't like the sound of the drum" ("Against Music")—but only because of the heavy tax burden such activities placed on commoners and also due to

14448-413: The same requirements as OTP keys. Digital versions of one-time pad ciphers have been used by nations for critical diplomatic and military communication , but the problems of secure key distribution make them impractical for most applications. First described by Frank Miller in 1882, the one-time pad was re-invented in 1917. On July 22, 1919, U.S. Patent 1,310,719 was issued to Gilbert Vernam for

14577-435: The secret numbers being changed periodically (this was called superencryption ). In the early 1920s, three German cryptographers (Werner Kunze, Rudolf Schauffler, and Erich Langlotz), who were involved in breaking such systems, realized that they could never be broken if a separate randomly chosen additive number was used for every code group. They had duplicate paper pads printed with lines of random number groups. Each page had

14706-403: The sequence starts again at A. The ciphertext to be sent to Bob is thus EQNVZ . Bob uses the matching key page and the same process, but in reverse, to obtain the plaintext . Here the key is subtracted from the ciphertext, again using modular arithmetic: Similar to the above, if a number is negative, then 26 is added to make the number zero or higher. Thus Bob recovers Alice's plaintext,

14835-537: The sum of the messages' sizes equals the size of the pad. Quantum key distribution also proposes a solution to this problem, assuming fault-tolerant quantum computers. Distributing very long one-time pad keys is inconvenient and usually poses a significant security risk. The pad is essentially the encryption key, but unlike keys for modern ciphers, it must be extremely long and is far too difficult for humans to remember. Storage media such as thumb drives , DVD-Rs or personal digital audio players can be used to carry

14964-495: The time, was suppressed under the Qin and died out completely under the Han , as its more radical adherents gradually dissolved and its most compelling ideas became absorbed by mainstream political thought. The influence of Mozi is still visible in many Han dynasty works written hundreds of years later. For example, the Confucian scholar Gongsun Hong describes the Confucian virtue of ren ("benevolence") in Mohist terms. Additionally, Mohist epistemology and philosophy of language had

15093-401: The tradition, while their more radical and anachronistic ones were gradually discarded, leading to their demise during the Han dynasty. According to Joseph Needham , Mozi (collected writings of those in the tradition of Mozi, some of which might have been by Mozi himself) contains the following sentence: 'The cessation of motion is due to the opposing force... If there is no opposing force...

15222-417: The use of a message authentication code can be used along with a one-time pad system to prevent such attacks, as can classical methods such as variable length padding and Russian copulation , but they all lack the perfect security the OTP itself has. Universal hashing provides a way to authenticate messages up to an arbitrary security bound (i.e., for any p > 0 , a large enough hash ensures that even

15351-513: The various possible readings of the ciphertext. If the key is not truly random, it is possible to use statistical analysis to determine which of the plausible keys is the "least" random and therefore more likely to be the correct one. If a key is reused, it will noticeably be the only key that produces sensible plaintexts from both ciphertexts (the chances of some random incorrect key also producing two sensible plaintexts are very slim). One-time pads are " information-theoretically secure " in that

15480-473: The war. A few British one-time tape cipher machines include the Rockex and Noreen . The German Stasi Sprach Machine was also capable of using one time tape that East Germany, Russia, and even Cuba used to send encrypted messages to their agents. The World War II voice scrambler SIGSALY was also a form of one-time system. It added noise to the signal at one end and removed it at the other end. The noise

15609-599: Was a multi-payload mission shared with QUESS, LiXing-1 research satellite, and ³Cat-2 Spanish science satellite. The main instrument on board QUESS is a " Sagnac effect " interferometer . This is a device that generates pairs of entangled photons, allowing one of each to be transmitted to the ground. This will allow QUESS to perform Quantum key distribution (QKD) – the transmission of a secure cryptographic key that can be used to encrypt and decrypt messages – to two ground stations. QKD theoretically offers truly secure communication. In QKD, two parties who want to communicate share

15738-424: Was akin to renouncing one's family, and indeed more strict Mohists living in Mohist communities as the school flourished may have exhibited such behavior. However, there is some scholarly debate over just how radical the provisions of universal love actually are, and, as can be seen from the example of Gongsun Hong above, the less radical components of the doctrine were eventually absorbed by mainstream thought. Mozi

15867-747: Was arrested and convicted in New York City in the 1950s, and the 'Krogers' (i.e., Morris and Lona Cohen ), who were arrested and convicted of espionage in the United Kingdom in the early 1960s. Both were found with physical one-time pads in their possession. A number of nations have used one-time pad systems for their sensitive traffic. Leo Marks reports that the British Special Operations Executive used one-time pads in World War II to encode traffic between its offices. One-time pads for use with its overseas agents were introduced late in

15996-404: Was distributed to the channel ends in the form of large shellac records that were manufactured in unique pairs. There were both starting synchronization and longer-term phase drift problems that arose and had to be solved before the system could be used. The hotline between Moscow and Washington D.C. , established in 1963 after the 1962 Cuban Missile Crisis , used teleprinters protected by

16125-479: Was electrical. In 1917, Gilbert Vernam (of AT&T Corporation ) invented and later patented in 1919 ( U.S. patent 1,310,719 ) a cipher based on teleprinter technology. Each character in a message was electrically combined with a character on a punched paper tape key. Joseph Mauborgne (then a captain in the U.S. Army and later chief of the Signal Corps ) recognized that the character sequence on

16254-619: Was known to have maintained a school for those who desired to become officials serving in the different ruling courts of the Warring States. Mozi was a carpenter and was extremely skilled in creating devices (see Lu Ban ). Though he did not hold a high official position, Mozi was sought out by various rulers as an expert on fortification. He was schooled in Confucianism in his early years, although he viewed Confucianism as being too fatalistic, with an overemphasis on elaborate celebrations and funerals, which Mozi considered to be detrimental to

16383-459: Was needed as they were used up fairly quickly. One problem with the system was that it could not be used for secure data storage. Later Vula added a stream cipher keyed by book codes to solve this problem. A related notion is the one-time code —a signal, used only once; e.g., "Alpha" for "mission completed", "Bravo" for "mission failed" or even "Torch" for " Allied invasion of French Northern Africa " cannot be "decrypted" in any reasonable sense of

16512-525: Was not the "amoral", mystical nature of the Daoists ; rather, it was a benevolent, moral force that rewarded good and punished evil. Similar in some ways to the beliefs systems found in the Abrahamic religions , Mozi believed that all living things lived in a realm ruled by Heaven, and Heaven possessed a will which was independent from, and higher than, the will of people. Thus Mozi wrote that "Universal love

16641-420: Was saddened when he saw the dyeing of pure white silk, which embodied his conception of austerity as simplicity and chastity. Most historians believe that Mozi was a member of the lower artisan class who managed to climb his way to an official post. Mozi was a native of the state of Lu (modern Tengzhou , Shandong), although for a time he served as a minister in the state of Song . Similar to Confucius , Mozi

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