How a Data Can be
Transmitted Securely
Presented by
Ekta Agrawal
What is Transmission
Security?
Transmission security is the capability to
send a message electronically from one
computer system to another computer
system so that only the intended recipient
receives and reads the message and the
message received is identical to the
message sent. The message would not be
identical if it was altered in anyway,
whether transmitted over faulty channels
or intercepted by an eavesdropper.
Data Transmission on Public
Network
What is Network ?
“Network is a collection and
connection of autonomous systems.”
With the advance of the Internet and
development of information technologies, many
conventional off-line services such as banking,
mailing and governmental affairs are migrating to
on-line ones. e-commerce, which treats
commercial activities by on-line, is the most
prominent example and intimately associated
with our real life.
The sensitive data and code
travels on public network so it requires security
to protect the data from unauthorized access.
SECURITY ATTACKS
Passive Attack- Does not
affect system
Active Attack- Affects the
system
Passive Attacks
Release of Message Contents-
Message can be easily understood.
examples-Telephone Conversation
Electronic mail message
Traffic Analysis- Masking of message
Through encryption techniques.
example- A text can be written by
exchanging places of alphabets.
Active Attacks
Masquerade- When one entity pretend
to be a different entity.
Replay-Passive captures of a data and
its retransmission to produce an
unauthorized effect.
Modification of Message-Some
portion of legitimate message is
altered.
Security Features
There are four aspects through which we
can provide security-
Authentication
Integrity
Non-repudiation
Confidentiality
Authentication means an authorized
user is using information. In online
transmission a registered user can transmit
the message.
Security Features
Integrity means data should be reached as
it was sent. During email whatever the
message is sent it should be reached exactly
same.
Non-repudiation means sender can
not deny after sending the message to
receiver. During email transmission a
sender can not deny for sending of that
message.
Confidentiality means message
should be kept private during transmission.
Encryption Techniques
a. Symmetric Cipher
b. Substitution Techniques
c. Transposition Techniques
d. Steganography
a. Symmetric Cipher
What is Encryption? A message in its original
form (plaintext) is encrypted into an
unintelligible form (cipher text) by a set of
procedures known as an encryption algorithm
(cipher) and a variable, called a key; and the
cipher text is transformed (decrypted) back
into plaintext using the encryption algorithm
and a key. ∆ε αρ
Dear Encryption Φρ ι ε ν Decryption Dear
δ ,
Friend, Friend,
Ι η α ϖε
I have I have
σε ε ν
seen your seen your
ψο υ ρ
message message
µ ε σσα
of … of …
γ ε ο φ
Original Symmetric Scrambled Symmetric Original
Data Key Data Key Data
What is encryption
Encryption C = EK(P)
Decryption P = EK-1(C)
EK is chosen from a family of
transformations known as a cryptographic
system.
The parameter that selects the individual
transformation is called the key K,
selected from a key space K.
b. Substitution Techniques
Letter of Plaintext are replaced by other letters
or by numbers or symbols.
Caesar Cipher
Hill Cipher
Polyalphabetic cipher.
Caesar cipher involves replacing each letter
standing three place further down the alphabet.
example:
plain text : meet me
cipher text : PHHW PH
b. Substitution Techniques
Hill Cipher involves m successive plain text,
letters and substitutes for them m cipher text
letters.
C = KP mod 26
where C and P are column vectors of
length 3,representing the plain text and cipher
text, and K is a 3*3 matrix representing the
encryption key.
for example consider the plaintext ”pay”
and use the encryption key 17 17 5
21 18 21
2 2 19
b. Substitution Techniques
The letters of plaintext “pay” are represented by
the vector
15
0
24
15 375 11
K
= LNS
=
0 = 819 mod26 13
24 486 18
b. Substitution Techniques
Polyalphabetic cipher. It uses a key that is as
long as the message. The key is a repeating
keyword.
example: if the keyword is deceptive, the message
“we are discovered save yourself” is encrypted as
follows:
key: deceptivedeceptivedeceptive
plaintext: wearediscoveredsaveourself
ciphertext: ZICVTWQNGRZGVTWAVZHCQYGMGJ
c. Transposition Techniques
Each letter of plaintext are replaced by
Rail Fence
Columnar transposition
Rail Fence is a technique in which the plaintext
is written down as a sequence of diagonals and
then read off as a sequence of rows.
Example: To encipher the message “meet me
after the party”
m e m a t r h p r y
e t e f e t e a t
The encrypted message is
MEMATRHPRYETEFETEAT
Transposition Techniques
Columnar transposition a message is written in
a rectangle row by row and read the message off,
column by column but permute the order of
columns.
Example-
Plaintext ”meet me after the party”
Key:4 3 1 2 5 6 7
me e t m e a
f t e r t h e
p a r t y
Ciphertext : EERTRTETAMFPMTYEHAE
d. Steganography
The one of the method to hide message is
steganography. Steganography conceal the
existence of message.
Examples
Character marking Selected letters of printed text
are overwritten in pencil. The marks are ordinarily
not visible unless the paper is held to an angle to
bright light.
Invisible Ink A number of substances can be used
to writing but leave no visible trace until heat or
some chemical is applied to the paper.
d. Steganography
Pin Punctures Small pin punctures on
selected letters are ordinarily not visible
unless the paper is held up in front of a
light.
Typewriter Correction ribbon It is used
between lines typed with a black ribbon.
The results of typing with the correction
tape are visible only under a strong light.
