Definition:
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 computer-centric 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 systems, 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.
How this works?
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 = Ek(P)
P = Dk(C)
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 make it easier to identify the communicating parties. If there is a third or fourth party to the communication, they will be referred to gas Carol and Dave. Mallory is a malicious party, Eve is an eavesdropper, and Trent is a trusted third party.
Modern cryptography concerns itself with the following four objectives:
1) Confidentiality (the information cannot be understood by anyone for whom it was unintended)
2) Integrity (the information cannot be altered in storage or transit between sender and intended receiver without the alteration being detected)
3) Non-repudiation (the creator/sender of the information cannot deny at a later stage his or her intentions in the creation or transmission of the information)
TYPES OF CRYPTOGRAPHIC ALGORITHMS
Secret Key Cryptography (SKC): Uses a single key for both encryption and decryption; also called symmetric encryption. Primarily used for privacy and confidentiality.
Public Key Cryptography (PKC): Uses one key for encryption and another for decryption; also called asymmetric encryption. Primarily used for authentication, non-repudiation, and key exchange.
Hash Functions: Uses a mathematical transformation to irreversibly “encrypt” information, providing a digital fingerprint. Primarily used for message integrity.
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