ENCRYPTION

COMENIUS 8th APRIL 2011
TRASFORMATION
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SECRECY
Encryption
Cryptos = hidden,
secret
Grafien = writing
 Transmit information in a confidential or encrypted
form. That is to say to intercept and decrypt an
encrypted message from a dual point of view.
 ENCRYPTION: The set of techniques that allow for
encryption and decryption of a text of a
cryptogram. “Garzanti Dictionary” (1972)
 Encryption is not intended to hide the message itself,
but its meaning.
 Branch of mathematics and computer science
 It uses the techniques of number theory and
information theory
● Encryption is an ancient science used to hide messages
between ancient kings, emperors, noblemen.
● The golden age of cryptography was during on the
second world war when Alan Turing, the father of
theoretical computer science, along with the research
group of the Bletchley Park formalized the
mathematics required for a systematic study of
ciphers.
CONCEALMENT OF THE MESSAGE
Steganografy
Steganos = covered
Grafien = writing
 Herodotus (400 B.C.)
 Comunication by writing on wooden tablets and then coated with wax
 Communication via slave with the head shaved
 Pliny the Elder (100 A.C.)
 Communication with invisible ink made from latex titimabo
 Gian Battista della Porta (1500)
 Comunication with boliled egg and invible ink
If the carrier is carefully searched the message can be
found :
 Scraping the wax tablets
 Shaving the head of the courier
 Bringing the sheet to a heat source
 Peeling egg
SECRECY IS LOST IN INTERCEPTION
 A cipher is a system capable of transforming a
plaintext (message) into unintelligible text (ciphertext
or cryptogram).
 To use a cipher, you must define two things: the
message encryption and decryption of the cryptogram.
Plaintext
(messagge)
CIPHER
Unintelligible text
(cryptogram)
• ATBASH: used in the Bible (Geremia’s Book)
Reversed Alphabet
Aleph-Taw Beth-Shin
A B C D E F G H I J K L MN O P Q R S T U V WX Y Z
z y x w v u t s r q p o n m l k j
i h g f e d c b a
BABEL(Jewish) = Sheshakh
• CAESAR CIPHER
 Svetonius (100-44 A.C.) “Vitae Caesarorum”
Each letter in the plaintext is replaced by a letter three
number of positions down the alphabet.
A B C D E F G H I J K L MN O P Q R S T U V WX Y Z
d e f g h i j
k l m n o p q r s t u v w x y z a b c
With the Caesar cipher decode the
following message
th duh kdssb wr kdyh brx
zlwk xv dw vfkrro
WE ARE HAPPY TO HAVE YOU
WITH US AT SCHOOL
• LEON BATTISTA ALBERTI (XV sec. A.C.)
 two disks, one inside the other
 the outer one 22 ordered letters and 4 numbers is
the plaintext
 the inner one 24 not ordered letters is the
ciphertext
With the Alberti cipher and (A, r) key,
decode the following message:
sh itbhl ycy rivcyrag marw
kgma zngwwp fkrz
WE HOPE YOU ENJOYED THIS
MATH CLASS IN ROME