Cryptography Tccicomputercoaching.com Cryptography is a method of storing and transmitting data in a particular form so that only those for whom it is intended can read and process it. Cryptography includes techniques such as microdots, merging words with images, and other ways to hide information in storage or transit. However, in today's computercentric world, cryptography is most often associated with scrambling plaintext (ordinary text, sometimes referred to as clear text) intocipher text (a process called encryption), then back again (known as decryption). Individuals who practice this field are known as cryptographers. The science or study of the techniques of secret writing, especially codeand cipher syste ms, methods, and the like. Compare cryptanalysis. There are five primary functions of cryptography today: Privacy/confidentiality: Ensuring that no one can read the message except the intended receiver. Authentication: The process of proving one's identity. Integrity: Assuring the receiver that the received message has not been altered in any way from the original. Non-repudiation: A mechanism to prove that the sender really sent this message. Key exchange: The method by which crypto keys are shared between sender and receiver. In cryptography, we start with the unencrypted data, referred to as plaintext. Plaintext is encrypted into cipher text, which will in turn (usually) be decrypted into usable plaintext. The encryption and decryption is based upon the type of cryptography scheme being employed and some form of key. For those that like formulas, this process is sometimes written as: C P = Dk(C)
=
Ek(P)
where P = plaintext, C = cipher text, E = the encryption method, D = the decryption method, and k = the key. In many of the descriptions below, two communicating parties will be referred to as Alice and Bob; this is the common nomenclature in the crypto field and literature to