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The Secrets of Cryptography

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S: The Secret of Cryptography

FC: The Secrets of Cryptography By YiLing K. and KaWing L. 8-05

1: Content Introduction Usage of Cryptography in the past Semaphore Modern Usage of Cryptography Modern Cryptography Algorithms Specific Cryptographic Schemes The Relations Between Mathematics and Cryptography Conclusion Bibliography

2: Introduction Cryptography are codes, they disguise words or meanings to a language that is needed to be decoded before the message can be properly read and understood. This Mixbook informs you about Cryptography, and it's "cryptic" ways. We hope you learn more about Cryptography from this book. Happy reading and enjoy!

3: Usage of Cryptography in the Past Back in the old days where war was fought constantly, codes were used so secret messages can be passed on without the enemy finding out immediately. The first type of "code", originated from Ancient Egypt. This code is hieroglyphs, the signs and letters used in Egyptian writing. Hieroglyphs are considered as codes not because it is not "something secret" but because it is a language so old no one can understand it anymore. It had not been used since the 4th century. Codes are used to communicate or signal to one another not necessarily with words but by sound or objects like flags(Semaphore).

4: Semaphore Is a code or an international system of visual signaling with two flags called Semaphore, it was used by sailors to message other ships before the invention of radios. It involves the person to hold one flag in each hand and taking a different body position to signal a letter or number as well as different signals. (As seen on the opposite page.) When signaling a number you must first do the "numerals" signal before doing the actual "number" signals. You must also use the "error" signal if you made a mistake on the previous signal so the receiver will know to ignore it. At the end of the message you must, like most languages end it with some sort of signal. In this case, the "End/Rest" Signal to notify the receiver that they are able to reply.

6: Modern Cryptography As technology evolves over the ages, the devices in both encrypting and decoding codes also evolve. Since the ending of World War II, and wars became slightly less frequent, codes were used for a new purpose, computers. From sending message to logging onto social networks or simply just surfing around the digital world, codes are present everywhere. They are important as some are used to protect our identity from theft in both open and closed networks. These devices are known as "Cryptosystems", and no matter what, the codes are within are breakable. In these systems are "Cryptograpic Algorithms", which we will develop more on the next pages.

7: Cryptographic Algorithms It was created to protect theft and alteration, also ensures that the message can only be read by the intended reader. This is a mechanism to prove that the messenger really did send the message. It is also used in a process of proving one's identity. Because the authentic things in the Internet is name or address based. There are three types that are considered algorithms, Secret Key Cryptography, Public Key Cryptography and Hash-functions. In all case the first encrypted data is known as plain-text. It is encrypted into safe text which usually turns into usable plain-text. There are different ways in classifying the algorithms. One can be they are categorized by the number of keys used for both encryption and decryption as well as the use of application.

8: Cryptographic Algorithms (continued.) There is the Secret Key Cryptography (SKC), it uses a single key for both encryption and decryption, the sender uses a key AKA a set of rules to encrypt the plain-text and the cipher-text, and sends the cipher-text to the receiver. The receiver applies the same key or set of rules to decrypt the message and retrieve the plain-text. SKC=Symmetric encryption. Public Key Cryptography (PKC), uses one key for encryption, another for decryption. The important part in the PKC, is that it doesn't matter which key is placed first, only a pair of keys is required. PKC is also known as asymmetrical encryption. In PKC one of the key is designated as the Public Key and can be shown to the public as much as the owner wants. The other key is designated as the "Private Key" and it is never revealed to other people. Hash-functions is used to encrypt information and uses mathematical transformations to irreversibly encrypt information. Can be called "message digest", and one-way encryption and are algorithms that uses no keys. A fixed length hash-value is created based on the plain-text that makes it impossible for either the content or length of the plain-text to be recovered. Hash-algorithms are basically used to provide a digital fingerprint of a files content often used to assure that the files have not been changed by a virus or an intruder. Hash functions are usually employed by many operating systems to encrypt passwords.

10: Specific Cryptographic Schemes | Why are there so many different types of cryptographic schemes? The answer is because each scheme is made for a specific use. Let's take hash functions for example. Hash functions is used for ensuring data protection because any change made to the content of the message will result the receiver calculating different hash values then the one placed in the transmission by the sender. Since it is unlikely that the two messages will have the same hash value, data integrity is ensured to a high degree of confidence. Secret Key Cryptography, is ideally suited to encrypting messages therefore providing privacy and confidentiality. The sender can generate a session key on a per message basis. To encrypt the message, the receiver will need the same session key to decrypt message.

11: Key exchange is a key application of Public Key Cryptography (no puns intended). Asymmetric schemes can be used for non-repudiation and user authentication. If the receiver can obtain the Session Key and encrypt it with a sender's Private Key, then only the sender could have sent message. PKC could theoretically also be used to encrypt messages although this is rarely done because the SKC operates at least 1000 times faster than the PKC.

12: The Relations Between Cryptography and Math | Cryptography is the study of hiding information using mathematical algorithms in such a way that the original information cannot be ascertained from the resulting 'cypher code' without knowledge of the specific 'key' required to undo the changes made by the algorithm. In some cases of public key exchange, one person will have to figure out a message that the other encrypted using mathematics. While decrypting a code using their own mathematic equation, there will be algebra and mathematical thinking involved. Even though in the past there were different ways of decrypting cryptography without using math, nowadays, we decrypt and solve problems using math only. Math has become a necessity in the world. Cryptography, if you think about it is basically composed of math itself and therefore it is related to math.

14: Conclusion | If we want to pass a message to a teammate in war without letting the enemy find out, we use cryptography. Children may send jokes in code to their friends. This is considered cryptography as well. Without us even realizing it, cryptography is starting to spread more and more over the world. It is starting to become more and more useful in our everyday lives as well. Even now, professors and mathematicians are figuring out new ways to decipher codes.

15: Bibliography Secret Codes by Helen Huckle Secret Codes for Kids by Robert Allen http://www.garykessler.net/library/crypto.html http://technet.microsoft.com/en-us/library/cc962030.aspx http://www.ams.org/notices/200708/tx070800972p.pdf

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Ka Wing Lai
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