CLARK UNIVERSITY College of Professional and Continuing Education (COPACE). Management Information Systems. Lection 05 Coding and encryption. Plan. Со ding Encryption. Information security.
may leave the old form, but changes, masks the contents. In order to read it is not enough to know only the algorithm, we must know the key
changes the form, but leaves the same content. For reading we must know the algorithm and coding table
If each color is coded:
by 2 bits, then we can code not more then 22= 4 colors,
by 3bits, then we can code not more then 23= 8 colors,
by 8 bits (= 1 byte), then we can code not more then 256 color.
Open text is a message, the text of which is necessary to make incomprehensible for outsiders.
Cipher is a set of invertible transformations of the set of the possible open data into the set of possible ciphertext carried out according to certain rules with the use of keys.
Original message: “A”Encrypted message: “B”Rule for encryption: “f”Encrypting scheme: f(A)=B
The encryption rule “f” cannot be arbitrary. It should be such that having the encrypted text “B” we could uniquely recover the open message using the rule “g”.
If “k” is a key, then f(k(A)) = B
For each key “k”, the transformation f(k) should be reversible, that is,g(k(B)) = A
«cryptos» - secret
«logos» - word
The science about the opening of ciphers
The science about the creation of ciphers
The basic scheme of classification:Cryptogram and Cryptography with a keyBy the nature of the key:Symmetric and AsymmetricBy the nature of the impacts on the data:Permutation and SubstitutionDepending on the size of the block of information:Stream and Block
Let us consider the payment of the client's goods or services by a credit card. The trading company must create one key for each customer and somehow give them the keys.
It is very inconvenient.