Coding of the email

Introduction

Why quantify the Email? It should be known that when you send an email from your station, this one forwards by several computers (the message is recorded on the hard drive of what is called waiters relay) before arriving on the computer of the recipient. This voyage is not without danger, indeed, derrières these computers hide, of the companies, the administrations or the not very scrupulous people who will be able to read your email (which by their design even and their protocols, circulates with overdraft, i.e. not quantified or quantified on Internet) “like a postcard without envelope”. The interest of coding is there, even if the risk of interception is weak, it is increasingly current and even if that which takes delivery of the message has a conscientiousness it is important to hide information relating on your professional secrecies or quite simply to your intimacy.

Symmetrical coding

To protect a confidential document, and to make sure that a person not - authorized will not have there access, it exists mainly two approaches (complementary):

the “Coding”, i.e. the fact of modifying the message to make it incomprehensible, except for its legitimate recipients.
the “Stéganographie”, i.e. the fact of dissimulating a document, which we will not develop here.

The first type of coding to be invented, well before the Christian era, is “symmetrical” coding: the transmitter and the receiver start by agreeing on a method of coding. For example, they can decide to replace such letter by such other: With by F, B per M, C by Z, etc Then, they must exchange the “key” of coding. If the algorithm is a simple permutation of letters, the key is the table of correspondence between the non-numerical letters and the quantified letters. One speaks about “symmetrical” coding because the transmitter and the receiver must know the same key, being used at the same time with the operations of coding and deciphering. Symmetrical coding is generally simple, fast, and it can be very sure… provided that a spy cannot discover the private key (secret)! However, before being able to communicate together, the transmitter and the receiver must agree on this private key. A solution consists in exchanging it in clean hand, but of course it is not always possible. This initial exchange of the key of coding is the principal weak point of symmetrical coding. Before the end of the 20th century, it was inconceivable that there exists another type of coding… until asymmetrical coding is invented.

Asymmetrical coding

The asymmetrical Coding, or public key coding is based on the existence of function mathematics to one way, i.e. it is easy to apply this function to a message, but it is extremely difficult to find this message as from the moment when it was transformed. Actually, one uses in asymmetrical coding of the functions with one way and “secret breach”. Such a function is difficult to reverse, unless having particular information, secret behavior: the private key. Starting from such a function, here how is held the “transaction”: Mr X wishes to receive coded messages of no matter whom, for that, it generates a function with one way and secret breach using an asymmetrical encryption algorithm (RSA for example). It diffuses it, but guard secrecy information making it possible to reverse this function. One thus speaks about public key for that which one diffuses (without worrying about safety) and key deprived for secret information (property of Mr X).

You still do not include/understand?

Each person has a set of two keys: it preserves the key of deciphering secretly, which one thus calls the private key, but it freely reveals the key of coding, which one calls the public key.

If Mr X wants to send a message has Mrs Y compared to a computer course which it missed, it starts with him to ask its public key (the disadvantage being that if the exchange not being done in clean hands, no matter who can the hand puts on the key). Thanks to this public key, Mr X quantifies his message, and sends the result to Mrs Y. Since Mrs Y is the only one to have the private key, it will be the only one with being able to decipher the message. The advantage compared to symmetrical coding is that the key of deciphering is never exchanged. The magic of the asymmetrical deciphering makes it possible two people to communicate together in an absolutely confidential way, even if a nonconscientious person allows herself to listen to all their communications, of the first to the last message.

The numerical signature

The numerical signature brings a safety complementary to coding. How to be sure that the email that you have just received in your box of reception is well that written by the declared shipper? Indeed, how to know that a joker did not intercept the message, changed it with its own way and made knowing itself it available to no matter whom a minimum in data processing there? The interception of a message a such bank statement could prove to be catastrophic, therefore the numerical Signature can be a true solution (in a legal framework where it gives a legal authenticity to your email).

But what an electronic signature (or numerical)?

It is acted in fact of a technical device derived from the coding which roughly speaking makes it possible to authenticate your messages. For that, it is necessary to obtain a personal certificate (emitted by an competent authority of Certification) based on a private key and a public key: the private key will be used electronically to sign emails and the public key makes it possible to quantify the messages which one will read with the private key stored on the computer (the recipient will be able to read your mail only by having possession of your public key).

This system thus makes it possible to prove that you are well the author of the message and that this one was not modified in the course of road but does not allow that the contents of message are confidential because everyone can have access has your public key and thus decode the message.

Obtaining a certificate is done in several stages (with the recognition of the authority of certification, the possession of a personal certificate, etc) but we will not make of it a fuller enumeration in this part. Note that it is easy to visualize these certificates with any specialized and qualified software.

We will never say enough that it is necessary, if the contents of your messages are somewhat sensitive, to code them, or in a term more adapted “to quantify them”.

See too

Cryptography
Coding | symmetrical Coding | asymmetrical Coding
Authentification | numerical Signature

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