Coding

In Cryptography, the coding (sometimes called wrongly encoding ) is the process thanks to which one can return the comprehension of an impossible document to any person who does not have the key (die) coding.

Although coding can make secret the direction of a document, other cryptographic techniques are necessary to communicate in a sure way. To check the Integrity or the authenticity of a document, one uses respectively a Message Authentification Codes (MAC) or a numerical Signature. One can also take into account the Analyze of traffic whose communication can be the object, since the reasons coming from the presence of communications can be the subject of a Reconnaissance of reason S. to make secret the presence of communications, one uses the Stéganographie. The safety of a system of coding must rest on the secrecy of the key of coding and not on that of the algorithm. The principle of Kerckhoffs supposes indeed that the enemy (or the person which wants to know the coded message) knows the algorithm used.

“Encoding”?

encoding The term “encoding” would be a Anglicisme, drawn from English encryption . In French, one must employ the word coding.
L' French Academy specifies that the word “encoding” is to be banished and it does not appear in its dictionary even if one can find it in the usual ones. However, “crypter” is often employed, especially in the passive, within the framework of the Paid television (one “crypt” of the chains). Moreover the Greek root kryptô (hidden) justifies its use fully each time coding, i.e. conversion into figures, is used to hide the message, the deciphering constitutes the conversion of the figures into letters to find the message, whereas decoding consists in discovering it.

In order to answer the interrogation “but for which reason not to employ this word? ”, the first argument consists in taking again the various definitions of the words to quantify/decipher and to decipher (see the article Cryptographie). To decipher indicating the fact “of finding the clear message corresponding to a coded message without having the key of deciphering”, the use such as it tends to develop pseudo-couple crypter/to decipher simply will make them tend to the state of synonym to quantify/decipher (just like english-speaking with encipher/decipher and encrypt/decrypt ). Thus rather than to gain a new word (in fact crypter ) without new direction, we will lose old feel, the current direction to decipher. Or how to lose while believing to gain…

Two principal types of coding

A system of coding is known as:

  • symmetrical when it uses the same key to quantify and decipher.

  • asymmetrical when it uses different keys: a pair made up of a public key , serving with coding, and as a private key , being used to decipher. The fundamental point supporting this public/private decomposition is calculative impossibility to deduce the private key from the public key.

The most known methods are the , the Triple OF the and AES for the symmetrical Cryptographie, and RSA for the asymmetrical cryptography, so called cryptography with public key.

The use of a symmetrical or asymmetrical system depends on the tasks to achieve. Asymmetrical cryptography presents two main interests: it removes the problem of protected transmission of the key, and it allows the electronic signature. It does not replace however the symmetrical systems because its computing times are definitely longer.

Difference between coding and coding

The operations of coding and coding belong to the Information theory. The essential difference lies in the will to protect information and to prevent third people from in the case of reaching the data coding. Coding consists in transforming information (data) towards a whole of words. Each one of these words makes up of symbols. The compression is a coding: one transforms the data towards a unit of adequate words intended to reduce the size but there is no will to dissimulate (although that is done implicitly while making more difficult of access the contents).

The " code" in the cryptographic direction of the term works on the level of semantics (words or sentences). For example, a code will be able to replace the word " avion" by a number. Coding works on more elementary components of the message, the letters or the bits, without being interested in the significance of the contents. A code requires conversion chart, such a called " dictionnaire" ( codebook in English). This being, " code" and " chiffrement" are often employed in a synonymous way in spite of this difference.

One can as consider as coding must resist a “intelligent” adversary which can tackle several manners whereas coding is intended for a transmission on a channel which can be potentially disturbed. This Bruit is a phenomenon Aléatoire which does not have intrinsic “intelligence” but can however be described mathematically.

Legal aspects

In Europe

In France

The use of PGP ( Pretty Good Privacy ), one of the first Software S of coding available on Internet, was a long time interdict in France, because considered until in 1996 as a weapon of war. The French legislation was then softened, and symmetrical coding with keys as large as 128 bits was authorized. Certain software, like GnuPG, could be used with any size of symmetrical key. Lastly, the Law of June 21st, 2004 for confidence in the digital economy completely liberalized the use of the means of cryptology; however the supply of keys of coding is subjected to declaration or authorization (see external bonds below).

In Switzerland

The Suisse was always tolerant with respect to cryptography, the government is favorable to its use and its development which represents an economic market. The Federal law on the Data protection (LPD) indicates that the significant personal data must be protected by adapted technical measures and that cryptography is recommended. Several flourishing companies in this field are Swiss: Kudelski (encoding for paying chains), Mediacrypt (owner of IDEA), Crypto AG and id Quantique (quantum Cryptography).

The Federal law of June 21st, 1991 on telecommunications (RS 784.10) indicates that (summarized legal text):

  • the development and the creation of cryptographic products (software or hardware) is subjected to no limitation
  • the use of the cryptographic software is subjected to no limitation
  • the cryptographic products just as the other equipment of telecommunications which can be connected to the public network must be in agreement with the technical standards ordered by the Federal council (put in conformity by the manufacturer or an inspection of the Federal Office of the Communication - OFCOM).
  • the cryptographic import/export of material is subjected to a request for certificate, this one authorizes the transactions. Specific measures are envisaged with regard to the military licenses and applications.

(see external bonds below).

See too

External bonds

  • cryptography in Switzerland
  • French Regulation as regards supply, of use and importation of means of cryptology (with the symmetrical direction here of '' coding '')
  • (cf Article 30)

Simple: Encryption

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