Cryptography: The Science of Making and Breaking Codes
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Ina cipher or cypher is an for performing or —a series of well-defined steps that can be followed as a procedure.
An alternative, less common term is encipherment.
To encipher or encode is to convert information into cipher or code.
In common parlance, "cipher" is synonymous with "", as they are both a set of steps that encrypt a message; however, the concepts are distinct in cryptography, especially.
Codes generally substitute different length strings of character in the output, while ciphers generally substitute the same number of characters as are input.
There are exceptions and some cipher systems may use slightly more, or fewer, more info when output versus the number that were input.
Codes operated by substituting according to a large which linked a random string of characters or numbers to a word or phrase.
For example, "UQJHSE" could be the code for "Proceed to the following coordinates.
The ciphertext message contains all the information of the plaintext message, but is not in a format readable by cipher systems ciphers and codes human or computer without the proper mechanism to decrypt it.
The operation of a cipher usually depends on a piece of auxiliary information, called a or, in traditional parlance, a cryptovariable.
The encrypting procedure is varied depending on the key, which changes the detailed operation of cipher systems ciphers and codes algorithm.
A key must be selected before using a cipher to encrypt a message.
Without knowledge of the key, it should be extremely difficult, if not impossible, to decrypt the resulting ciphertext into readable plaintext.
If the algorithm is symmetric, the key must be known to the recipient and sender and to no one else.
If the algorithm is an asymmetric one, the enciphering key is different from, but closely related to, the deciphering key.
There are many theories about how the word "cipher" may have come to mean "encoding".
The concept of zero which was also called "cipher"which is now common knowledge, was alien to medieval Europe, so confusing and ambiguous to common Europeans that in arguments people would say "talk clearly and not so far fetched as a cipher".
Cipher came to mean concealment of clear messages or encryption.
Besides "cifra", they use word "broj" for a number.
Ibrahim Al-Kadi concluded that the Arabic word sifr, for the digit zero, developed into the European technical term for encryption.
As the decimal zero and its new mathematics spread from the Arabic world to Europe in thewords derived from sifr and zephyrus came to refer to calculation, as well as to privileged knowledge and secret codes.
According to Ifrah, "in thirteenth-century Paris, a 'worthless fellow' was called a '.
Within technical discussions, however, the words "code" and "cipher" refer to two different concepts.
Codes work at the level of meaning—that is, words or phrases are converted into something else and this chunking generally shortens the message.
An example of this is the which was used to shorten long telegraph messages which resulted from entering into commercial contracts using exchanges of.
Another example is given by whole word ciphers, which allow the user to replace an entire word with a symbol or character, much like the way Japanese utilize Kanji Japanese characters to supplement their language.
Ciphers, on the other hand, work at a lower level: the level of individual letters, small groups of letters, or, in modern schemes, individual bits and blocks of bits.
Some systems used both codes and ciphers in one system, using to increase the security.
In some cases the terms codes and ciphers are also used synonymously to substitution and transposition.
Historically, cryptography was split into a dichotomy of codes and ciphers; and coding had its own terminology, analogous to that for ciphers: " encoding, codetext, decoding" cipher systems ciphers and codes so on.
However, codes have a variety of drawbacks, including susceptibility to and the difficulty of managing a cumbersome.
Because of this, codes have fallen into disuse in modern cryptography, and ciphers are the dominant technique.
Algorithms used earlier in the are substantially different from modern methods, and modern ciphers can liquidity withdrawals certificates and deposit of classified according to how they operate and whether they use one or two keys.
They include simple such as and such as a.
For example, "GOOD DOG" can be encrypted as "PLLX XLP" where "L" substitutes for "O", "P" for "G", and "X" for "D" in the message.
Transposition of the letters "GOOD DOG" can result in "DGOGDOO".
These simple ciphers and examples are easy to crack, even without plaintext-ciphertext pairs.
Simple ciphers were replaced by ciphers such as the which changed the substitution alphabet for every letter.
For example, "GOOD DOG" can be encrypted as "PLSX TWF" where "L", "S", and "W" substitute for "O".
With even a small amount of known or estimated plaintext, simple polyalphabetic substitution ciphers and letter transposition ciphers designed for pen and paper encryption are easy to crack.
It is possible to create a secure pen and paper cipher based on a though, but the apply.
During the early twentieth century, electro-mechanical machines were invented to do encryption and decryption using transposition, polyalphabetic substitution, and a kind of "additive" substitution.
Inseveral rotor disks provided polyalphabetic substitution, while plug boards provided another substitution.
Keys were easily changed by changing the rotor disks and the plugboard wires.
Although these encryption methods were more complex than previous schemes and required machines to encrypt and decrypt, other machines such as the British were invented to crack these encryption methods.
In a symmetric key algorithm e.
The uses a combination of substitution and transposition techniques.
Most block cipher algorithms are based on this structure.
In an asymmetric key algorithm e.
An adversary can use multiple computers at once, for instance, to increase the speed of for a key i.
As the key size increases, so does the complexity of to the point where it becomes impractical to crack encryption directly.
Since the desired effect is computational difficulty, in theory one would choose an and desired difficulty level, thus decide the key length accordingly.
An example of this process can be found at which uses check this out reports to suggest that a symmetric cipher with 128an asymmetric cipher with 3072 bit keys, and an with 512 bits, all have similar difficulty at present.
Al-Kadi, "Cryptography and Data Security: Cryptographic Properties of Arabic", proceedings of the Third Saudi Engineering Conference.
Riyadh, Saudi Arabia: Nov 24-27, Vol 2:910-921.
The Universal History of Numbers: Cipher systems ciphers and codes Prehistory to the Invention of the Computer.
Aldrich, GCHQ: The Uncensored Story of Britain's Most Secret Intelligence Agency, HarperCollins July 2010.
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Inq's Cipher Wheel
Codes and Cipher Systems. The Ceasar Cipher - This cipher (aka. shift cipher) is a substitution cipher, where letters are replaced by a letter with a fixed shift in the alphabet. Pigpen Cipher - The pigpen cipher (aka. masonic cipher) is a very simple substitution cipher, that goes back all the way to the 18th century.
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