Difference between Active attack and Passive attack

1. Security
Lecture 3

2. Difference between Active attack and Passive
attack
What is cryptographic Security Attack?
A cryptographic attack is a method for circumventing the security
of a cryptographic system by finding a weakness in a code, cipher, cryptographic protocol
or key management scheme. This process is also called “cryptanalysis ”
.
Types of Security Attack
There are two types of Security Attack in cryptography: Active Attack dna Passive Attack.
Types of Active Attack:lpeR ,edareuqsaM
ay Attack, Modification of message, Denial of Services.
Types of Passive Attack: sisylanA ciffarT ,tnetnoc egassem fo esaeleR
.

4. Passive Attack
• The goal of the attacker is to obtain information that is being
transmitted. A telephonic conversation, an electronic mail message
and a transferred file may contain sensitive or confidential
information. In this type of passive attack, message cannot modify by
attacker. Attacker just read the message and then release the
message. There may be a delay to reach message at receiver end.
• For example, B sent message to A, A receives message. But before
receiving message, message was read by unauthorized person.
• This kind of passive attack cannot by recognize/identified during
massage transmission. It does not affect the system, just monitor data
in network.

5. Passive Attack Release of message content

6. • Intruders checks the contents of message or other information, even
if they captured the message but could not extract the information
from the message. The opponent might observe a pattern of message
to get the location, or any clue regarding the origin of message.
Passive attack is very difficult to detect, because they do not involve
any alteration of the data.
Traffic Analysis

7. Active Attack
• Masquerade
• A masquerade take place when an attacker pretends to be an
authentic user. Authentication sequence can be captured & replayed
after a valid authentication sequence has taken place. It generally
done to gain access to a system, or steal information from system.
•

8. Active Attack
• Replay Attack
• Replay involves the passive capture of data unit and its subsequent
retransmission to produce an unauthorized effect. A replay attack is also
known as playback attack where attacker repeatedly keeps on transmitting
valid data again and again to make the network jam or delayed the
transmission of data.
• For example, A and C have bank account in Bank B. A send request to bank
B for fund transfer in C’s account. C capture the message produce
unauthorized effect of message and get benefits twice for fund transfer.
One is from original message and second is from unauthorized message.

9. Active Attack

10. Active Attack
• Modification of Message
Some portion message is altered, or that message is delayed or recorded to produce unauthorized effect. When content
of message modified after sender sends it but before it reaches to concerned receiver, such type of attack is called
modification of message.
For example, A message is “Virat will play and also captain in next match” is modified to “Rohit will play and also captain
in next match.”

11. Active Attack
• Denial of Services
• Denial of service attack means making the network unavailable for
the user those who want to communicate securely. Flood the entire
network or server with traffic until shutdown occurs because if
overload.

12. Difference between Active Attack and Passive Attack

13. • Hill Cipher is polyalphabetic substitution cipher. This technique was developed
by mathematician Laster Hill. Hill cipher based on linear algebra. Input of this
technique are keyword and plain text. Keyword is given in matrix form.
Hill Cipher
Rules of encryption is as follows:
Step-1: Assign a number to each character of the Plain-Text, like
(a = 0, b = 1, c = 2, … z = 25). As per given table.
For Example, Plain Text = SUNDAY ⇒ S = 18, U = 20, N = 13, D = 3,
A = 0, Y = 24

14. Hill Cipher
Step-2: 2x2 or 3x3 key matrix is given,

15. Hill Cipher
• Step-3: Make a group of plain text as per given key matrix size. Each
pair of plain text multiply with key matrix.
• For Example, Plain Text = SUNDAY
• If key matrix is 2 x 2, Plain text divided in into group of 2 alphabets:
SU ND AY
• If key matrix is 3 x 3, Plain text divided in into group of 3 alphabets:
SUN DAY

16. Hill Cipher
• Step-4: Multiplication of plain text matrix and key word matrix
generate new matrix.
• Step-5: Newly generated matrix values modules with 26.
• Step-6: After modules 26, matrix values assign characters using rule
no 1 table. It generates final cipher text.
•

17. Rules of decryption for Hill Cipher
• Step-1: Assign a number to each character of the cipher text, like (a =
0, b = 1, c = 2, … z = 25). As per given table.
• For Example, Cipher Text = SUNDAY ⇒ S = 18, U = 20, N = 13, D = 3, A
= 0, Y = 24

18. Rules of decryption for Hill Cipher
• Step-2: Find the inverse of given key matrix (2x2 or 3x3),
• Step-3: Make a group of Cipher text as per given key matrix size. Each pair of Cipher text multiply with
inverse key matrix.
• For Example, Plain Text = SUNDAY
• If key matrix is 2 x 2, Plain text divided in into group of 2 alphabets: SU ND AY
• If key matrix is 3 x 3, Plain text divided in into group of 3 alphabets: SUN DAY
• Step-4: Multiplication of cipher text matrix and inverse key word matrix generate new matrix.
• Step-5: Newly generated matrix values modules with 26.
• Step-6: After modules 26, matrix values assign characters using rule no 1 table. It generates final plain text.

19. Example of Hill Cipher (Key Matrix 2x2)
• Encryption Process

20. Example of Hill Cipher (Key Matrix 2x2)
• Decryption Process

21. Example of Hill Cipher (Key Matrix 3x3)

22. • The Columnar Transposition Cipher is a form of transposition cipher in
which plain text represent in matrix form. Columnar Transposition
involves writing the plaintext out in rows, and then reading the
ciphertext off in columns one by one. Here I have explained
encryption and decryption process of columnar transposition cipher.
Columnar Transposition Cipher
Rules of Encryption Process
Example: = htgnel yeK( KCAH = yeK ,NEERG SI EERT :txeTnialP
4
)
Step-1 :Width of the rows and the permutation of the columns are usually defined by a keyword

23. Columnar Transposition Cipher
Step-2: Keyword HACK is of length 4 (so the rows are of length 4), and the permutation is defined by the alphabetical
order of the letters in the keyword. In this case, the order would be “3 1 2 4”.
Step-3: The message is written out in rows of a fixed length.
Step-4: Any spare spaces are filled with nulls or left blank or placed by a character (Example: _)

24. Columnar Transposition Cipher
Step-5: Finally, the message is read off in columns, in the order specified by the keyword.

25. Rules of Decryption Process for Columnar
Transposition Cipher
As per above example:
Cipher Text: R I R _ E S E _ T _ G N E _ E_
Key = HACK (Key length= 4)
Step1: To decipher it, the recipient has to work out the column lengths by dividing the message length by the key length.

26. Rules of Decryption Process for Columnar
Transposition Cipher
• Step-2: Then, write the cipher text in columns again, then re-order
the columns by reforming the keyword. Read matrix row wise to get
plain text.