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Cryptography

## Overview [1]#

Cryptography (or cryptology; from Greek κρυπτός, kryptos, "hidden, secret"; and γράφω, gráphō, "I write", or -λογία, -logia, respectively) s the practice and study of techniques for secure communication in the presence of third parties (called adversaries)

### The story#

We often see and use Cryptography where the desire is for Alice to send a Message to Bob in presence of (the adversaries) Eve and Mallory.

is the practice and study of hiding information. In modern times, cryptography is considered a branch of both mathematics and computer science, and is affiliated closely with information theory, computer security, and engineering. Cryptography is used in applications present in technologically advanced societies; examples include the security of ATM cards, computer passwords, and electronic commerce, which all depend on cryptography.[1]

In Cryptography discussions we typically make a Computational Hardness Assumption.

### Cryptography Objectives#

There are some differing opinions on Cryptography Objectives

### Cryptography and Security#

"Security is only as strong as the weakest link, and the mathematics of Cryptography is almost never the weakest link. The fundamentals of Cryptography are important, but far more important is how those fundamentals are implemented and used. Arguing about whether a key should be 112 bits or 128 bits long is rather like pounding a huge stake into the ground and hoping the attacker runs right into it. You can argue whether the stake should be a mile or a mile-and-a-half high, but the attacker is simply going to walk around the stake. Security is a broad stockade: it’s the things around the cryptography that make the cryptography effective. " - Preface to Practical Cryptography (the 1st Edition)

### Cryptographic Systems#

Cryptographic Systems are what provide Cryptography. Taking any Cryptographic Primitive or isolated Cryptography piece will not allow meeting the objectives. Most breaches are caused by a Cryptographically Weakness that has been introduced in the Cryptographic process, often by improper implementation.

### Cryptographic Hash Functions#

A Cryptographic Hash Function or Message Digest is the output of a Secure Hash Algorithm which permeates a source message of variable length into a highly unique, fixed-length digital fingerprint (signature). Cryptographic Hash Functions cannot be used to reconstitute the original message but can be used by one participant to prove that another participant possesses some secret material (for example, a password). This proof can then be used to establish an identity.

### More Information#

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