[permalink] [id link]

In cryptography, a substitution cipher is a method of encryption by which units of plaintext are replaced with ciphertext, according to a regular system ; the " units " may be single letters ( the most common ), pairs of letters, triplets of letters, mixtures of the above, and so forth.

from
Wikipedia

## Some Related Sentences

cryptography and substitution

Poe's success in

__cryptography__relied not**so**much on his knowledge**of**that field**(**his**method**was limited**to****the**simple__substitution__cryptogram**),**as on his knowledge**of****the**magazine**and**newspaper culture**.****In**classical

__cryptography__

**,**one

**of**

**the**earliest

**encryption**methods was

**the**simple

__substitution__

**cipher**

**,**where

**letters**in

**a**message were systematically

**replaced**using some secret scheme

**.**

**In**

__cryptography__

**,**an S-Box

**(**Substitution-box )

**is**

**a**basic component

**of**symmetric key algorithms

**which**performs

__substitution__

**.**

The story involves

__cryptography__**with****a**detailed description**of****a****method**for solving**a**simple__substitution__**cipher**using letter frequencies**.****In**classical

__cryptography__

**,**

**the**running key

**cipher**

**is**

**a**type

**of**polyalphabetic

__substitution__

**cipher**in

**which**

**a**text

**,**typically from

**a**book

**,**

**is**used

**to**provide

**a**very long keystream

**.**

**In**classical

__cryptography__

**,**

**the**Hill

**cipher**

**is**

**a**polygraphic

__substitution__

**cipher**based on linear algebra

**.**

cryptography and cipher

**In**

__cryptography__

**,**

**a**block

__cipher__

**is**

**a**deterministic algorithm operating on fixed-length groups

**of**bits

**,**called blocks

**,**

**with**an unvarying transformation that

**is**specified

**by**

**a**symmetric key

**.**

**In**

__cryptography__

**,**

**a**

__cipher__

**(**or cypher )

**is**an algorithm for performing

**encryption**or decryption —

**a**series

**of**well-defined steps that can

**be**followed as

**a**procedure

**.**

**In**non-technical usage

**,**

**a**

**"**

__cipher__

**"**

**is**

**the**same thing as

**a**

**"**code "; however

**,**

**the**concepts

**are**distinct in

__cryptography__

**.**

**In**

__cryptography__

**,**key size or key length

**is**

**the**size measured in bits

**of**

**the**key used in

**a**cryptographic algorithm

**(**such as

**a**

__cipher__).

**In**

__cryptography__

**,**

**encryption**

**is**

**the**process

**of**transforming information

**(**referred

**to**as

**plaintext**) using an algorithm

**(**called

**a**

__cipher__)

**to**make it unreadable

**to**anyone except those possessing special knowledge

**,**usually referred

**to**as

**a**key

**.**

**In**

__cryptography__

**,**

**the**International Data Encryption Algorithm

**(**IDEA )

**is**

**a**block

__cipher__designed

**by**James Massey

**of**ETH Zurich

**and**Xuejia Lai

**and**was first described in 1991

**.**

The polyalphabetic

__cipher__was**,**at least in principle**,**for it was not properly used for several hundred years**,****the****most**significant advance in__cryptography__since before Julius Caesar's time**.**
* MARS

**(**__cryptography__**),****a**block__cipher__that was IBM's submission**to****the**Advanced Encryption Standard process**.****In**

__cryptography__

**,**RC4

**(**also known as ARC4 or ARCFOUR meaning Alleged RC4

**,**see below )

**is**

**the**

**most**widely used software stream

__cipher__

**and**

**is**used in popular protocols such as Secure Sockets Layer

**(**SSL )

**(**

**to**protect Internet traffic )

**and**WEP

**(**

**to**secure wireless networks ).

The term cypherpunk

**,**derived from__cipher__**and**punk**,**was coined**by**Jude Milhon as**a**pun**to**describe cyberpunks who used__cryptography__**.****In**

**the**history

**of**

__cryptography__

**,**Typex

**(**alternatively

**,**Type X or TypeX ) machines were British

__cipher__machines used from 1937

**.**

**In**

__cryptography__

**,**

**a**transposition

__cipher__

**is**

**a**

**method**

**of**

**encryption**

**by**

**which**

**the**positions held

**by**

**units**

**of**

**plaintext**

**(**

**which**

**are**commonly characters or groups

**of**characters )

**are**shifted

**according**

**to**

**a**

**regular**

**system**

**,**

**so**that

**the**

**ciphertext**constitutes

**a**permutation

**of**

**the**

**plaintext**

**.**

**In**other words

**,**two successive applications

**of**ROT13 restore

**the**original text

**(**in mathematics

**,**this

**is**sometimes called an involution

**;**in

__cryptography__

**,**

**a**reciprocal

__cipher__).

**In**

__cryptography__

**,**Triple DES

**is**

**the**

**common**name for

**the**Triple Data Encryption Algorithm

**(**TDEA or Triple DEA ) block

__cipher__

**,**

**which**applies

**the**Data Encryption Standard

**(**DES )

__cipher__algorithm three times

**to**each data block

**.**

**In**

__cryptography__

**,**

**a**Caesar

__cipher__

**,**also known as Caesar's

__cipher__

**,**

**the**shift

__cipher__

**,**Caesar's code or Caesar shift

**,**

**is**one

**of**

**the**simplest

**and**

**most**widely known

**encryption**techniques

**.**

**In**

__cryptography__

**,**

**a**stream

__cipher__

**is**

**a**symmetric key

__cipher__where

**plaintext**digits

**are**combined

**with**

**a**pseudorandom

__cipher__digit stream

**(**keystream ).

As

**with**other attacks in__cryptography__**,**stream__cipher__attacks can**be**certificational**,**meaning they aren't necessarily practical ways**to**break**the**__cipher__but indicate that**the**__cipher__might have other weaknesses**.**

cryptography and is

The latter

__is__more cumbersome**to**use**,****so**it's only employed when necessary**,**for example in**the**analysis**of**arbitrary-precision arithmetic algorithms**,**like those used in__cryptography__**.**
* symmetric key algorithms

**(**Private-key__cryptography__**),**where**the**same key__is__used for**encryption****and**decryption**,****and**
It

__is__one**of****the**earliest practical examples**of**key exchange implemented within**the**field**of**__cryptography__**.**
The introduction

**of**DES__is__considered**to**have been**a**catalyst for**the**academic study**of**__cryptography__**,**particularly**of**methods**to**crack block ciphers**.****"**An astonishing share

**of**

**the**open literature in

__cryptography__in

**the**1970s

**and**1980s dealt

**with**

**the**DES

**,**

**and**

**the**DES

__is__

**the**standard against

**which**every symmetric key algorithm since has been compared

**.**

Elliptic curve

__cryptography__**(**ECC )__is__an approach**to**public-key__cryptography__based on**the**algebraic structure**of**elliptic curves over finite fields**.**
Elliptic curve

__cryptography____is__vulnerable**to****a**modified Shor's algorithm for solving**the**discrete logarithm problem on elliptic curves**.**
Factorization

**of**large integers__is__believed**to****be****a**computationally very difficult problem**,****and****the**security**of**many modern__cryptography__systems__is__based upon its infeasibility**.**
The Communications-Electronics Security Group

**(**CESG )**of**GCHQ provides assistance**to**government departments on their own communications security: CESG__is__**the**UK national technical authority for information assurance**,**including__cryptography__**.**
Although related

**,****the**distinctions among these measures mean that**a**random variable**with**high Shannon entropy__is__not necessarily satisfactory for use in an extractor**and****so**for__cryptography__uses**.**
Information security uses

__cryptography__**to**transform usable information into**a**form that renders it unusable**by**anyone other than an authorized user**;**this process__is__called**encryption****.**
The presumed difficulty

**of**this problem__is__at**the**heart**of**widely used algorithms in__cryptography__such as RSA**.**
The problem often arises in resource allocation where there

**are**financial constraints**and**__is__studied in fields such as combinatorics**,**computer science**,**complexity theory**,**__cryptography__**and**applied mathematics**.**

cryptography and method

The

__method__was followed shortly afterwards**by**RSA**,**an implementation**of**public key__cryptography__using asymmetric algorithms**.**
During

**the**early history**of**__cryptography__**,**two parties would rely upon**a**key using**a**secure**,**but non-cryptographic**,**__method__**.**
Although sequences that

**are**closer**to**truly random can**be**generated using hardware random number generators**,**pseudorandom numbers**are**important in practice for their speed in number generation**and**their reproducibility**,****and**they**are**thus central in applications such as simulations**(**e**.**g.,**of**physical systems**with****the**Monte Carlo__method__**),**in__cryptography__**,****and**in procedural generation**.**
Lagrange polynomials

**are**used in**the**Newton – Cotes__method__**of**numerical integration**and**in Shamir's secret sharing scheme in__cryptography__**.****In**traditional symmetric key

__cryptography__

**,**this problem wasn't an issue as it was implicitly assumed that some

**"**secure

**"**

__method__

**of**key distribution guaranteed key authenticity

**.**

It introduced

**a**radically new__method__**of**distributing cryptographic keys**,****which**went far toward solving one**of****the**fundamental problems**of**__cryptography__**,**key distribution**.**
It introduced

**a**radically new__method__**of**distributing cryptographic keys**,**that went far toward solving one**of****the**fundamental problems**of**__cryptography__**,**key distribution**.****In**

__cryptography__

**,**

**a**zero-knowledge proof or zero-knowledge protocol

**is**an interactive

__method__for one party

**to**prove

**to**another that

**a**

**(**usually mathematical ) statement

**is**true

**,**without revealing anything other than

**the**veracity

**of**

**the**statement

**.**

This fabrication

__method__has potential for applications in quantum__cryptography__**(**i**.**e**.****single**photon sources )**and**quantum computation**.**
Key exchange

**(**also known as**"**key establishment ")**is**any__method__in__cryptography__**by****which**cryptographic keys**are**exchanged between users**,**allowing use**of****a**cryptographic algorithm**.****In**

__cryptography__

**,**Russian copulation

**is**

**a**

__method__

**of**rearranging

**plaintext**before

**encryption**

**so**as

**to**conceal stereotyped headers

**,**salutations

**,**introductions

**,**endings

**,**signatures

**,**etc

**.**

* An asymmetric-key cryptosystem

**is**published**by**Whitfield Diffie**and**Martin Hellman who disclose**the**Diffie – Hellman key exchange__method__**of**public-key agreement for public-key__cryptography__**.**
Clark Stanley's Snake Oil

**.****In**__cryptography__**,**snake oil**is**any commercial cryptographic__method__or product considered**to****be**bogus or fraudulent**.**
Shortly afterward

**,**Netscape's SSL technology was widely adopted as**a**__method__for protecting credit card transactions using public key__cryptography__**.****In**cryptology

**,**

__cryptography__

**is**

**a**

__method__used

**to**transform

**a**message into an obscured form

**so**it cannot

**be**understood

**.**

* The

__method__for changing between polynomial**and**normal bases**,****and**similar transformations**,**for purposes**of**coding theory**and**__cryptography__**.****In**

__cryptography__

**,**

**ciphertext**stealing

**(**CTS )

**is**

**a**general

__method__

**of**using

**a**block

**cipher**mode

**of**operation that allows for processing

**of**messages that

**are**not evenly divisible into blocks without resulting in any expansion

**of**

**the**

**ciphertext**

**,**at

**the**cost

**of**slightly increased complexity

**.**

The main use

**of****the**tables was in statistics**and****the**experimental design**of**scientific experiments**,**especially those that used**the**Monte Carlo__method__**;**in__cryptography__**,**they have also been used as nothing up my sleeve numbers**,**for example in**the**design**of****the**Khafre**cipher****.**0.343 seconds.