Transcript The Evolution of Secret Writing

The Evolution of Secret Writing
楊子陞
李柏勳
馬天祥
陳孟彙
B9209010
B9209024
B9209002
B9209049
What is Steganography ?
Derived from the
Greek words stegano,
meaning “covered,”
and graphcin,
meaning “to write.”
Various forms of Steganography
The ancient Chinese wrote messages on
fine silk, which was then scrunched into a
tiny ball and covered in wax.
The Italian scientist Giovanni Porta
described how to conceal a message
within a hard-boiled egg.
Various forms of Steganography
The thithymallus plant could be used as an
invisible ink. Many organic fluids behave
in a similar way, because they are rich in
carbon and therefore char easily.
Modern spies who have run out of
standard issue invisible ink to improvise by
using their own urine.
How can secret writing affect history ?
secret writing saved Greece from being
conquered.
Be used in the war
What is Cryptography
Greek word “kryptos”
“hidden”
Not to hide the message
Two kinds of cryptography:
Transposition
the letters of the message are
simply rearranged
Substitution
give each alphabet which we
know a new meaning
Transposition
A word is rearranged randomly by us.
For example, a word “are” which has 6
different way to be rearranged, e.g., are,
aer, rea, rae, ear, era.
The drawback of this way is that too many
different ways we can’t understand it’s
meaning immediately.
Another way is using the “rail fence”
transposition
For example:
Life science is the main trend of the world
Lfs i neshmi t edfhwrd
iececI t e anrnote ol
our cipher
Lfsineshmitedfhwrdiececiteanrnoteol
Picture
the scytale is a wooden staff around which a
strip of leather or parchment is wound.
Substitution
To pair letters of the alphabet at random, and
then substitute each letter in the original
massage with its partner.
If we apply the principle to the roman alphabet,
we can pair letters as follows:
A D H I K M O R S U W Y Z
V X B G J C Q L N E F P T
Another form of substitution is often called the
Caesar shift cipher.
Plain alphabet:
abcdefghIjklmnopqrstuvwxyz
Cipher alphabet:
DEFGZJKLMNOPQRSTUVWXYZABC
The drawback of Caesar shift cipher is that
someone only try 25times can find its cipher
Another way is rearrange alphabets
randomly, and then there are
400,000,000,000,000,000,000,000,000
kinds of differences.
The other way is using a keyword or keyphrase
to process, and the left alphabets are processing
in turn as normal.
Plain alphabet:
abcdefghIjklmnopqrstuvwxyz
Cipher alphabet:
J U L I S CAERTVWXYZBDFGHKMNOPQ
L I FESCNOPQRSTUVWXYZABDGHJK
Sender
receive
Key
key
algorithm
Plaintext
ciphertext
algorithm
plaintext
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