Caesar Cipher (2024)

Homepage

Crypto

Index

Glossary

Enigma

Hagelin

Fialka

Rotor

Pin-wheel

Voice

Data

Hand

OTP

EMU

HSM

Mixers

Phones

Bulk

FILL

Codebooks

Algorithms

Chips

Cryptanalysis

Toys

World War II

Countries

Czechoslovakia

DDR

Germany

Netherlands

Russia

Switzerland

USA

USSR

Yugoslavia

Manufacturers

ANT

Aristo

Ascom

AT&T

BBC

Bosch

Compumatica

CryptoAG

Datotek

Fox-IT

Gemalto

Gretag

Harris

HELL

ITT

Lorenz

Lugagne

MEL

Mils

Motorola

Mykotronx

Nokia

OMI

Omnisec

Philips

PTT

R&S

Racal

RanData

Raytheon

RCA

Safenet

Secunet

Siemens

STK

Tadiran

Tait

TCC

Telefunken

Telsy

Teltron

Thales

Transvertex

TST

Ultra Electronics

Utimaco

Zellweger

OTHER

Spy radio

Burst encoders

Intercept

Covert

Radio

Telex

Telephones

People

Agencies

Manufacturers

DONATE

Publications

Standards

For sale

Kits

Shop

News

Events

Wanted

Contact

About us

Links


Caesar Cipher

Transposition cipher

The Caesar Cipher is one of the most basic methods forencrypting and decrypting a text.The method is named after Julius Caesar (55BC) and is a substitutioncipher in which each letter of the plaintext is shifted up or down the alphabet by a fixed number of positions.The method is also known as Caesar's Cipher, Caesar's Code,Caesar Shift and Shift Cipher.Julius Caesar, who used it in his private correspondence, shifted each letter of the plaintext down by 3 positions.

In this case, The letter D becomes an A, E becomes B, etc. At the receiving end,all the recipient has to do, is shift each letter by the same fixed number inreverse direction. This means that A becomes D, B becomes E, etc. For this reason, the cipher is sometimes called a 'shift cipher' or a 'rotation',in which case the Caesar Cipher is identified as ROT3 (rotation by 3 positions).


Security

In Caesar's days, the ROT3 algorithm probably offered resonable securityas most of Caesar's opponents were illiterate and even if they were ableto read,they would probably have thought that it was written in an unknown foreignlanguage. Today, the Caesar Cipher offers absolutely no securitywhatsoever. It is easily broken by hand and even the more complexVigenère Ciphercan not withstand frequency analysis and mathematical key length tests [1].


ROT13

A well known variant – which is also used in some computer software – is ROT13.As this rotates the alphabet by 13 positions (exactly half the available 26 letters),the cipher becomes reversible or reciproke.In this case the letter A becomesan N and the N (13 places further) becomes an A.

There are many variants of the Caesar Cipher. Caesar's nephew Augustus forexample, used a right-shift of one position (A becomes B, B becomes C, etc.).Other variants are the Reverse Caesar Cipher, which is alwaysreciprocal, and the Vigenère Cipher,which uses a variable shift.Furthermore a combination of the latter two is known asthe Beaufort Cipher.


Modern use

The ROT13 method is still widely used on Usenet, often for obscuring offensivetext rather than for serious encryption. Nevertheless, some well known softwarevendors have used ROT13 in the past for storing passwords.Despite the fact the Caesar Cipher offers virtually no protection today,Rajib Karim was convicted in the UK in 2011 of 'terrorism offences'. He useda variant of the Caesar Cipher when discussing plots to blow up British Airwaysplanes, rather than a more sophisticated program such as Mujhaddin Secretsor PGP. Although he had access to the latter, he didn't trust it andcame up with this own scheme, implemented in Microsoft Excel [2].


References

Wikipedia, Caesar Cipher
Retrieved February 2015.
The Register, BA jihadist relied on Jesus-era encryption
Retrieved February 2015.


Further information


Any links shown in red are currently unavailable. If you like the information on this website, why not make a donation? © Crypto Museum. Created: Sunday 22 February 2015. Last changed: Thursday, 18 February 2021 - 18:35 CET.