Sabtu, 26 Februari 2011


Cryptography is the study of mathematical techniques related to aspects of information security such as confidentiality, data integrity, and authentication.

Cryptography Objectives

to provide security services (which is also named as the security aspects) as follows:
1. Secrecy (confidentiality), is a service intended to keep the message can not be read by parties who are not eligible. In cryptography, the service is realized by encrypting the message into ciphertext. For example the message "Please come at 8" encoded into "TrxC # 45motyptre!%." Another term matching with confidentiality is secrecy and privacy. More about the encryption method will be discussed in subsequent chapters.
2. Integrity of data (data integrity), is a service that ensures that the message is still the original / intact or had never been manipulated during shipping. In other words, the security aspect can be expressed as a question: "Is the message received is genuine or not changed (modified)?". To maintain data integrity, the system must have the ability to detect manipulation of messages by the parties are not entitled, such as insertion, deletion, and other data pensubsitusian into the actual message. In cryptography, the service is realized by using digital signatures (digital signatures). Messages that have been signed by implying that the message sent is the original. More about digital signatures will be discussed in the chapter Digital Signature.
3. Authentication (authentication), is a service related to identification, both to identify the truth of the parties to communicate (user authentication or entity authentication) as well as identify the source of the truth of the message (data origin authentication). The two parties must communicate with each other to authenticate one another so that he can verify the source of the message. Messages sent via the communication channel should also be authenticated origin. In other words, the security aspect can be expressed as a question: "Is the message received actually originated from the right sender?". Authenticate the message source is implicitly also gives assurance of data integrity, because if the message has been modified means that the source of the messages is not true. Therefore, data integrity service is always combined with the authentication service ource message. In cryptography, the service is realized by using digital signatures (digital signatures). Digital signatures stating the source of the message.
4. Denial (non-repudiation), is a service to prevent entities that communicate to denial, which denies the message sender or recipient of a message delivery has denied receiving messages. For example, suppose that gives the message sender to the recipient's authority to make a purchase, but then he denied giving such authority. As another example, suppose an owner's bid to store gold carp that he would sell his gold. However, gold prices suddenly dropped dramatically, and he denied having made an offer to sell gold. In this case, the gold shops nirpenyangkalan necessary procedures to prove that the owner of gold has made a lie.

History of Cryptography
Cryptography has a long history. Complete information on the history of cryptography can be found in David Kahn's book, entitled The Codebreakers. 1000 pages thick book that is written in detail the history of cryptography from the use of cryptography by Egyptians 4000 years ago (in the form of hieroglyph that is not standard on priamid) through the use of cryptography in the 20th century. Historically there are four groups of people who contributed to the development of cryptography, where they use cryptography to ensure confidentiality in communication important message, namely the military (including intelligence and spy), diplomatic circles, the author of the diary, and lovers (lovers). Among these four groups, the military is the most important contribution is important because sending messages in an atmosphere of war requires encryption and decryption techniques are complicated. History of cryptography is largely a history of classical cryptography, the encryption method that uses paper and pencil or perhaps with the help of a simple mechanical device. In general, classical cryptographic algorithms are grouped into two categories, namely algorithms transposition (transposition cipher) algorithm and substitution (substitution cipher). Transposition Cipher change the order of the letters in the message, whereas substitution ciphers replace each letter or group of letters with a letter or group of other letters. History records the use of classic cryptographic cipher transposition by the army of Sparta in Greece at the beginning of the year 400 BC. They use a tool called scytale. Scytale consists of a long paper from papyrus leaves wrapped in a cylinder of a certain diameter (diameter silender declare an encryption key). Messages are written horizontally, line by line if the tape is removed, then the letters in it were arranged randomly to form a secret message. To read the message, the recipient must have looped back to wrapping the paper into a cylinder diameter equal to the diameter cylinder sender. Sedangkang substitution algorithm, the earliest and simplest is the Caesar cipher, used by the ancient Greek king, Julius Caesar. The trick is to replace every character in the alphabet with a character that is located on the next three positions in the arrangement of the alphabet. Cryptography is also used for security purposes. Members of the church in the early days of Christianity using cryptography to protect the religious writings of disruption or political authority of the dominant culture at the time. Perhaps the most famous is the "Number of the Beast (Number of the Beast) in the New Testament. The number "666" declare how cryptographic (ie encrypted) to hide the dangerous message; the experts believe that the message refers to the Roman Empire
Modern Cryptography is triggered by the development of digital computer equipment. With
digital computer, the more complex ciphers be very likely to be able to
generated. Unlike classical cryptography, which encrypts the character by character
(By using the traditional alphabet), modern cryptographic operations on binary strings.
Complex cipher like DES (Data Encryption Standard) and the discovery algorithm
RSA is the most modern cryptographic algorithms known in the history of cryptography
modern. Modern cryptography is not only related to the technique of confidentiality
message, but also gave birth to concepts such as digital signatures and digital certificates.
In other words, modern cryptography not only provide security aspects
confidentiality, but also other security aspects like authentication, data integrity, and
Cryptography developing such a way that gave birth to the opposite field of cryptanalysis. Cryptanalysis (cryptanalysis) is the science and art to solve chiperteks into plaintext without knowing the key used. Perpetrators called kriptanalis. If a cryptographer (cryptographer) transform plaintext into ciphertext with a key algorithm and then reverse a kriptanalis trying to solve these ciphertexts to find the plaintext or key. Cryptology (cryptology) is the study
on cryptography and cryptanalysis.
Historical parallels with the history of cryptanalysis cryptography (cryptanalysis), namely the field of science and art to solve the ciphertext. The word "cryptanalysis" itself is still relatively new (first expressed by William Friedman in 1920), but the actual technique of cryptanalysis has been there since the 9th century. Is a scientist at the Century IX Arab named Abu Yusuf Yaqub ibn Ishaq Ibn As-Sabbah ibn 'Omran Ibn Ismail al-Kindi, or better known as Al-Kindi, who wrote a book about the art of breaking the code. In a book entitled "Treatise fi al-Mu'amma Istikhraj (Manuscript for the Deciphering Cryptographic Messages), he wrote the script to decipher secret codes. In the book Al-Kindi introduced or decoding technique, or password that is difficult to solve. He also classifies the secret password as well as explaining the science Arabic phonetics and syntax. Most importantly, in this book he introduced the use of several statistical techniques to crack secret codes (quoted from Republika Online, 16 June 2006).
What was done by Al-Kindi in cryptanalysis technique called frequency analysis, which is a technique to solve the cipher based on the frequency of occurrence of characters in the message and its relation to frequency of occurrence of characters in the alphabet. Frequency analysis is based on the fact that the cipher failed to hide the statistical occurrence of the characters in cipherteksnya. For example, in the English letter "E" is the letter most often appear in sentences berbahas England. If there are letters in the ciphertext is most likely to occur, then most likely in the plainteksnya letter is the letter E (the technique will dijleaskan in Chapter 4). Various classical cipher successfully solved with this frequency analysis techniques. Frequency analysis techniques are still used in modern cryptanalysis, but because of increasingly complicated cipher, then the mathematical approach remains dominant in doing cryptanalysis. The development of any computer help kriptanilisis activities. History records kriptanalissi brilliant results like solving Zimmermann Telegram that brought the United States into the arena of World War I, and the solving of the Enigma cipher contributed to ending World War II.

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