What is Cryptography?

There are a number of terms associated with a cryptosystem. These include cryptology, cryptography, cryptanalysis, and steganography. Cryptology is the study of secure communications, which encompasses cryptography, cryptanalysis, and steganography. Cryptography is the branch of cryptology dealing with the design of algorithms for encryption and decryption. These algorithms are intended to ensure the secrecy and/or authenticity of messages and data. Cryptanalysis is the branch of cryptology dealing with the breaking of a cipher to recover information, or forging encrypted information that will be accepted as authentic. A cipher is an algorithm for encryption and decryption. A cipher replaces a piece of information with another object, with the intent of concealing meaning. Typically, a secret key governs a replacement rule. Lastly, steganography is a method of cryptology that hides the existence of a message. [Newman, 2002, p. 65-66]

Figure 1. Cryptography (SUPINFO International University, 2016)

The word “cryptography“ is derived from Greek and when literally translated, means “secret writing.” Before the advent of digital communications, cryptography was used primarily by the military for the purposes of espionage. With the advances in modern communication, technology has enabled businesses and individuals to transport information at a very low cost via public networks such as the Internet. This development comes at the cost of potentially exposing the data transmitted over such a medium. Therefore, it becomes imperative for businesses to make sure that sensitive data is transferred from one point to another in an airtight, secure manner over public networks. Cryptography can help us achieve this goal by making messages unintelligible to all but the intended recipient. [Atreya, n.d., ¶ 2]

Encryption refers to the transformation of data in “plaintext“ form into a form called “ciphertext,” which renders it almost impossible to read without the knowledge of a “key,” which can be used to reverse this transformation. The recovery of plaintext from the ciphertext requires the key, and this recovery process is known as decryption. This key is meant to be secret information and the privacy of the ciphertext depends on the cryptographic strength of the key. [Atreya, n.d., ¶ 3]

Figure 2. Encryption (Tectrade, 2015)

Cryptography is the study of “mathematical“ systems involving two kinds of security problems: privacy and authentication. A privacy system prevents the extraction information by unauthorized parties from messages transmitted over a public channel, thus assuring the sender of a message that it is being read only by the intended recipient. An authentication system prevents the unauthorized injection of messages into a public channel, assuring the receiver of a message of the legitimacy of its sender. [Diffie & Hellman, n.d.]

Figure 3. Privacy (Cosmos Auto Repair, 2014)

A channel is considered public if its security is inadequate for the needs of its users. A channel such as a telephone line may therefore be considered private by some users and public by others. Any channel may be threatened with eavesdropping or injection or both, depending on its use. In telephone communication, the threat of injection is paramount, since the called party cannot determine which phone is calling. Eavesdropping, which requires the use of a wiretap, is technically more difficult and legally hazardous. In radio, by comparison, the situation is reversed. Eavesdropping is passive and involves no legal hazard, while injection exposes the illegitimate transmitter to discovery and prosecution. [Diffie & Hellman, n.d.]

Reference:

Atreya, Mohan.  “Introduction to Cryptography.”  Retrieved on May 25th, 2017 from URL:  https://web.cs.ship.edu/~cdgira/courses/CSC434/Fall2004/docs/course_docs/IntroToCrypto.pdf

Diffie, Whitfield & Martin E. Hellman, n.d.  “New Directions in Cryptography.”  Retrieved on May 25th, 2017 from URL:  http://crypto.csail.mit.edu/classes/6.857/papers/diffie-hellman.pdf

Newman, C. Robert.  “Enterprise Security 2nd Ed.”  Pearson Education 2003, New Jersey.

Hope you’ll find this post informative.

peace and blessings,

Bekim

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