CYBER SECURITY TECHNIQUES
(CONTINUED)
LECTURE 5
CYBER SECURITY TECHNIQUES
• There
are
numerous
encryption
techniques
available
for
protecting
sensitive
data.
Substitution
and
transposition techniques are the primary
techniques of codifying the plaintext
message to obtain the ciphertext.
• These
two
approaches
are
the
fundamental building blocks of encryption
techniques and can be combined to form a
product cipher.
CYBER SECURITY TECHNIQUES
• The substitution technique differs
from the transposition technique in that
the substitution technique replaces the
plaintext
characters
for
other
characters, numbers, and symbols.
• In
contrast,
the
Transposition
techniques don't change the character
but rather shift the symbol's position.
WHAT IS SUBSTITUTION TECHNIQUE?
• The substitution technique involves replacing
letters with other letters and symbols. In simple
terms, the plaintext characters are substituted,
and additional substitute letters, numerals, and
symbols are implemented in their place.
• We have studied two examples of this
technique, which are Caesar cipher, and Play
fair
• The substitution technique's weakness is that it
is highly predictable, and if the translation table
is known, the substitution may be disrupted
WHAT IS TRANSPOSITION TECHNIQUE?
• In the transposition technique, the characters'
identities are kept the same, but their positions are
altered to produce the ciphertext.
• A transposition cipher in cryptography is a type of
encryption that scrambles the locations of characters
without altering the characters themselves.
• Transposition ciphers produce a ciphertext that is a
permutation of the plaintext by rearranging the
components of the plaintext in accordance with a
regular method.
• A bijective function is utilized to the character
locations to encrypt data, and an inverse function is
employed to decode data.
FEATURES OF THE
TECHNIQUE
TRANSPOSITION
1. The keys that are closer to the proper key in the
transposition cipher technique can reveal plain text.
2. The transposition cipher approach does not exchange
one sign for another but rather moves the symbol.
3. The two most common types of transposition cipher are
keyless and keyed transpositional cipher.
4. The Rail Fence Cipher is an excellent instance of a
transposition technique.
5. The position of the character is modified in the
transposition cipher technique, but the character's identity
remains unchanged.
KEY
DIFFERENCES
BETWEEN
SUBSTITUTION
TECHNIQUE
AND
TRANSPOSITION TECHNIQUE
• There
are
various
key
differences
between
Substitution
Technique
and
Transposition Technique. Some main key
differences between these techniques are as follows:
1. The substitution approach employs a substitute for
the plaintext characters to transform them
into ciphertext. In contrast, the transposition
technique essentially rearranges the plaintext
characters.
2. The substitution technique aims to change the
entity's identification. In contrast, the transposition
technique affects the entity's position instead of its
identity.
KEY DIFFERENCES BETWEEN
SUBSTITUTION TECHNIQUE AND
TRANSPOSITION TECHNIQUE
3. The substitution technique replaces every character
with an integer, character, and symbol. In contrast, in
the transposition technique, every character has been
positioned from its actual position.
4. Some algorithms that use the substitution technique
are monoalphabetic, polyalphabetic substitution cipher,
and Playfair cipher. In contrast, the transposition
techniques utilize the keyed and keyless transpositional
ciphers.
5. The plaintext in the substitution strategy could be
easily determined using the low-frequency letter. In
contrast, in the transposition technique, the keys close
to the right key lead to the plaintext discovery.
RAIL FENCE CIPHER
• In the rail fence cipher, the plain text is written
downwards and diagonally on successive "rails" of
an imaginary fence, then moving up when we
reach the bottom rail.
• When we reach the top rail, the message is written
downwards again until the whole plaintext is
written out. The message is then read off in rows.
• Many websites claim that the rail-fence cipher is a
simpler "write down the columns, read along the
rows" cipher.
• This is equivalent to using an un-keyed columnar
transposition cipher
EXAMPLE:
We are discovered safe your self
The key : AUTHOR
EXAMPLE 1:
EXAMPLE 2:
HERE IS ANOTHER MESSAGE:
THE BRITISH SOLD CAPTURE DENIGMA MACHINES TO FORMER
COLONIES
ROUTE TRANSPOSITION
• Route Cipher is a type of transposition cipher, which is a
method of encryption that involves rearranging the order
of letters in a message.
• In a route cipher, the plaintext is first written out in a grid
of given dimensions, then read off in a pattern given in
the key.
ROUTE TRANSPOSITION
• For example, using this plaintext:
• “We are discovered flee at once”
W R I O R F EO E
E E S V E LAN J
ADCEDETCX
• The key might specify "spiral inwards, clockwise, starting
from the top right". That would give a cipher text of:
EJX CTE DEC DAE WRI ORF EON ALE VSE
EXAMPLE 2:
•
lets encrypt the plaintext:
"abort the mission, you have been spotted".
The Answer:
• First we need to decide on the number of columns
we are going to use, lets say 5.
• Notice how we have used nulls at the end of the
message to make a nice rectangle.
•
Second write down the letters as shown below:
EXAMPLE 2:
•
With a route of reading down the columns we get the ciphertext:
"ATSYV NTBHS OESEO EIUBP DRMOH EOXTI NAETX".
•
With a route of spiralling inwards counter-clockwise from the
bottom right we get: "XTEAN ITROB ATSYV NTEDX OEHOM
EHSOE SPBUI".
•
Decryption
To decrypt a message received that has been encoded with the
Route Cipher, we need to know the route used and the width or
height of the grid. We then start by constructing a blank grid of the
right size, and then place the ciphertext letters in the grid following
the route specified.
EXAMPLE 2:
•
For example, to decrypt the ciphertext "RAEWE CREDX ESIDO V"
with the route spiral inwards counter-clockwise from the top right, with
a grid width of 4, we follow the process shown below