1.1 Definition
Cryptography is a word coming from Grec which is divide by two
parts Cryptus which is mean Keep (Secret) and Graphy is
define as written. By those Grec words we define Crytography as a way to keep
secret a message (Written) using some mathematics notions, principaly number
theory. other way, cryptography is a way and techniquess to study how to make
secure information using mathematical notions with concepts such as
confidentiality, data integrity, entity authentication and data origin
authenticate.
1.1.1 Mathmaticaly. We define Cryptography as a
set of five G = (P, C, Ck, Dk, k) where
1. G is our main set of cryptography;
2. P is a the clear message that we want to keep secret;
3. C is a finite set of text blocks can be digit
4. Ck is an encryption function;
5. Dk is a function of decryption;
6. k is the key, that we use to keep secret a
message.
According to [STI06], in order to define just cryptography as
a way to secure message, there is also other words which are related to
Cryptography.
1. Cryptogramme is one way use through the media (newspaper,
magazine, so on) to keep secret a message. Is technic, is based on an
encryption message is just a shifting of letters.
2. Cipher is a secret way to write a message using
subtitution or transposition of letter specially in form of symbol.
3. Cryptanalysis is a science where people analysis a
cryptogram with goal to decrypt a message keep there.
4. Cryptology is science wich combine cryptography and
cryptanalysis.
5.
Section 1.2. Security concepts Page 3
Cryptolect is a secretive language form used by a subculture
dissimiller for a message.
This field is remaind not new for all persons but most of
people use cryptography without knowing that they use this field of science to
keep secret a message, communication whatsoever. Authentification,
confidentiallity, non-repudiation and integrity those are conditions if you
need a good security of message in term of secrecy. These conditions in the
other way is called primitive function, because its make sure the
security of information using some mathematical notions.
1.2 Security concepts
Let's define those concepts:
1. The authentification is a function that ensure
verification that the person who are communicate are still the same people. All
time we are dealing with this function, we are still answer in same important
questions. The answer in those question, make a new functions which are connect
directly in the security system where its make a verification of certification,
control of access, the key manager, proof of knowledge and proof of
disclosure
2. Integrity is a function use for data verification that is
if during the transmission the data stay the same as in the beginning. To do
it, one part must have the ability to detect data manipulation by unauthorized
parties.
3. Non-repudiation, this service in the security of
information, is the most important such that when someone use or send data, the
system registers an action and after, we can verify the information and
reconstruct the scheme of communication so that the person cannot lie the
action he did. It means also the disponibility of information in the system.
4. Confidentiality is a function or service used to verify
the content of information, if there are not modification on it. (goal to keep)
from the persons who are authorized.
Cryptography, science including all security for sharing
datas, use those principals in terms of safety. As we defined a cryptography as
a set G of five elements, to secure a message or to provide the writing to
become unreadable, to apply those concepts in terms of implementation, we use
the most import element which is a key in the set G. To build a good secure
system, we need to compute a good secure key. To build this key, we follow a
mathematics concept of modulo in Z. For that, we have two kind of Keys: a
private and public key. Around those two types, we define what we call
cryptosystem.
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