Cryptography Definitions

Cryptography comes from Greek: "cryptos" means "secret" (secret), while "graphein" means "writing" (writing). So cryptographic means "secret writing" (hieroglyph). So cryptography is defined as the science and art to maintain the confidentiality of a message by encrypting it kebentuk way that you can not understand anymore what it means. The word "art" in this definition comes from the historical fact that in the early days of history kroptografi, each person may have a unique way to conceal messages. The ways these may vary at each actor cryptography so any way to write secret messages, the message has its own aesthetic values ​​that evolved into an art cryptographic secret message. The above definition may be appropriate in the past where cryptography is used for safety critical communications such as communications among the military, diplomats and spies. However, the current cryptography more than just privacy, but also for the purpose of data integration, authentication, and non-repudiation.
A. Menezes defines cryptography as the science that studies mathematical techniques related to aspects of information security such as confidentiality, data integrity and authentication. This definition can be considered as a comparison between the cryptography and cryptography in the past the present. Today cryptography developed into a discipline of science itself because cryptographic techniques can be mathematically formulated so that it becomes a formal method.

*Plaintext and ciphertext Messages are the data or information which can be read and understood its meaning. Another name of the message is the plaintext (the plaintext) or clear text (cleartext). Messages can be either data or information transmitted (via courier, telecommunication channels, etc.) or stored in a recording medium (paper, storage, etc.). Messages that are stored not only in the form of text, but also to shape the image (image), voice, sound (audio), video or other binary file. Unintelligible messages to their meaning by the other party, then the message can be encoded into another form that can not be understood. Messages encrypted form called ciphertext (ciphertext) or cryptogram (cryptogram). Ciphertext can be transformed back into its original plaintext message to be received can be read. 

*Sender and Receiver Data communication involves the exchange of messages between two entities. Sender (sender) is the entity that sends a message to another entity. Receiver (receiver) is the entity that receives the message. An entity here can be people, machines (computers), credit cards, and so forth. So people can exchange messages from other people (eg
  Alice communicates with the Budi), whereas in computer networks, machines (computers) to communicate with machines (eg, ATM machines communicate with the server at the Bank). The sender would want the message can be sent securely ie he believes that other parties can not read the contents of the messages he sends. The solution is to encode the message into ciphertext. 

*Encryption and Decryption The process of encoding plaintext into ciphertext is called encryption (encryption) or enciphering. While the restore ciphertext to the original plaintext is called decryption (decryption) or deciphering. Encryption and decryption can be applied both to the messages sent and the messages saved. 

*Cipher and Key Cryptographic algorithms called ciphers are the rules for enchipering and deciphering, or mathematical function used for encryption and decryption. Some ciphers require different algorithms for enciphering and deciphering. The concept underlying mathematical cryptographic algorithm is a relation between two sets is the set containing the element-element set containing the plaintext and ciphertext. Encryption and decryption is a function which maps elements between these two sets. For example, P and C represent states ciphertext plaintels the encryption function E mapping P to C, E (P) = C
And decryption function D maps C to P, D (C) = P Because encryption and decryption process returns a message to the initial message, then the following equation must be true, D (E (P)) = P Security of cryptographic algorithms is often measured by the number of work (word) needed to break the ciphertext into plaintext without knowing the key used. This work can diekivalenkan with time, memory, money, and others. More and more work is needed also means the longer it takes, the stronger cryptographic algorithms, which means the safe is used to encrypt a message. If cryptographic security is determined to maintain the confidentiality of the algorithm, the algorithm is called algorithm kriptografinya restricted, which restricted the algorithm has its own history in cryptography. Restricted algorithm is usually used by a group of people to exchange messages with each other. They create an encryption algorithm and encryption algorithm is only known by members of that group only. But the algorithm is restricted no longer appropriate today, because every time a member of the group out, then the cryptographic algorithm must be replaced again.

Modern Cryptography overcome the above problems by using the key, which in this case the algorithm is no longer kept secret, but the key must be kept confidential. Key (key) is a parameter that is used for enciphering and deciphering transformation. The key is usually a string or a row of numbers. By using the key K, the encryption function can be written as:
EK (P) = C
and decryption functions can be written as:
DK (C) = P
And both of these functions satisfy:
DK (EK (P)) = P

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* Cryptography System Cryptography form a system called cryptographic system. Cryptographic system (cryptosystem) is a collection of cryptographic algorithms, all possible plaintext and ciphertext, and keys. In the cryptographic system, the cipher is only one component only.
* Bugs Tapper (eavesdropper) is a person who tries to capture the message in transmission. The purpose of bugs is to get as much information concerning the cryptographic systems used to communicate with the intent to break the ciphertext.
  * Cryptanalysis and Cryptology Cryptography developing such a way that gave birth to the opposite field of cryptanalysis. Cryptanalysis (crypanalysis) is the science and art to break the ciphertext into plaintext without knowing the key used. Perpetrators named kriptanalis. If a cryptographer (cryptographer) transform plaintext into ciphertext with an algorithm and key, then instead of a kriptanalis trying to solve these ciphertexts to find the plaintext or key. Cryptology (cryptology) is the study of cryptography and cryptanalysis.
* Cryptography System Cryptography form a system called cryptographic system. Cryptographic system (cryptosystem) is a collection of cryptographic algorithms, all possible plaintext and ciphertext, and keys. In the cryptographic system, the cipher is only one component only.
* Bugs Tapper (eavesdropper) is a person who tries to capture the message in transmission. The purpose of bugs is to get as much information concerning the cryptographic systems used to communicate with the intent to break the ciphertext.
* Cryptanalysis and Cryptology  
Cryptography developing such a way that gave birth to the opposite field of cryptanalysis. Cryptanalysis (crypanalysis) is the science and art to break the ciphertext into plaintext without knowing the key used. Perpetrators named kriptanalis. If a cryptographer (cryptographer) transform plaintext into ciphertext with an algorithm and key, then instead of a kriptanalis trying to solve these ciphertexts to find the plaintext or key. Cryptology (cryptology) is the study of cryptography and cryptanalysis.
* Objectives Cryptography
Cryptography aims to provide security services as follows:  
1. Secrecy (confidentiality), is a service that aims 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.  
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 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.  
3. authentication (authentication), is a service related to identification, both to identify the truth of the parties to communicate and identify the true source of the message. The two parties must communicate with each other to authenticate one another so that he can ensure the truth of the message source. Messages sent via the communication channel should also be authenticated origin. 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 message source authentication service. In cryptography, the service is realized by using digital signatures. Digital signatures stating the source of the message. 
 4. Non-repudiation, are services to prevent entities that communicate to denial, which denies the message sender or recipient of a message delivery has denied receiving messages. For instance gives the message sender to the recipient's authority to make purchases, but he has denied giving such authority.