USN
1 P E
E C
PESIT Bangalore South Campus
Hosur road, 1km before Electronic City, Bengaluru -100
Department of Electronics and Communications
TEST - 1
Date
: 18-02-2014
Subject & Code : Network Security & 10EC832
Name of faculty : Mrs. Shubha Raj K.B.
Marks : 50
Section: 8th CSE A & B
Time : 8.30 to 10 AM
Note: Answer any FIVE Questions
1 a
Classify the various security attacks and define them.
Security attacks
5
USN
1 P E
PESIT Bangalore South Campus
Hosur road, 1km before Electronic City, Bengaluru -100
Department of Electronics and Communications
E C
USN
1 P E
E C
PESIT Bangalore South Campus
Hosur road, 1km before Electronic City, Bengaluru -100
Department of Electronics and Communications
b With a neat diagram, explain network security model.
Network Security Model
5
 All the techniques for providing the security has 2 components
 A security-related transformation:
 ex: Encryption of messages and decryption
 Secrete information
 Ex: Encryption key
 Third party is needed to achieve the secure transmission
 Distributing the secret key
 There are 4 basic tasks in designing a particular security service
1. Design a suitable algorithm for the security transformation
2. Generate the secret information (keys) used by the algorithm
3. develop methods to distribute and share the secret information
4.
2 a
specify a protocol to be used by the principals that make use of the security algorithm
and secret information to achieve a particular security service
What are the principles elements of a public-key cryptosystems
–
a public-key, which may be known by anybody, and can be used to encrypt messages,
and verify signatures
–
a private-key, known only to the recipient, used to decrypt messages, and sign (create)
signatures
5
USN
1 P E
E C
PESIT Bangalore South Campus
Hosur road, 1km before Electronic City, Bengaluru -100
Department of Electronics and Communications

is asymmetric because
–




those who encrypt messages or verify signatures cannot decrypt messages or create
signatures
Encryption algorithm
Decryption algorithm
Plaintext
Ciphertext
b Define the following terms with relation to cryptography.
i) Algorithm
ii) Key
iii) Plaintext
iv) Steganography v) Cryptanalysis
•
plaintext - original message
•
key – secrete info used in cipher known only to sender/receiver
•
encipher (encrypt) - converting plaintext to ciphertext
–
•
Encryption: converting original message into a form unreadable by unauthorized
individuals
decipher (decrypt) - recovering ciphertext from plaintext
5
USN
1 P E
E C
PESIT Bangalore South Campus
Hosur road, 1km before Electronic City, Bengaluru -100
Department of Electronics and Communications
•
cryptography - study of encryption principles/methods
•
cryptanalysis ( breaking the code) - study of principles/ methods of
–
•
3
deciphering ciphertext without any knowledge of the encryption details.
Steganography: “covered writing” Insert secrete binary info into the data during digitization
process
List and briefly define categories of security services and security mechanisms
 Authentication - assurance that the communicating entity is the one claimed
 Access Control - prevention of the unauthorized use of a resource
 Peer entity authentication
 Data origin authentication
 Data Confidentiality –protection of data from unauthorized disclosure
 Data Integrity - assurance that data received is as sent by an authorized entity
 Non-Repudiation - protection against denial by one of the parties in a communication
 Availability Service - accessible and usable by an authorized system entity
 Denial of Service attacks
 Virus that deletes files
specific security mechanisms:
 encipherment,
 digital signatures: To prove source as well as integrity of data unit
 access controls,
 data integrity,
 authentication exchange,
 traffic padding: The insertion of bits into gaps in a data stream to frustrate traffic
analysis attempts,
 routing control: Enables selection of particular physically secure routes for certain data.
 Notarization: The use of a trusted third party to assure certain properties of a data
exchange.
 pervasive security mechanisms:
 trusted functionality: Which perceived to be correct with respect to some criteria.
10
USN
1 P E
E C
PESIT Bangalore South Campus
Hosur road, 1km before Electronic City, Bengaluru -100
Department of Electronics and Communications
 security labels:
 event detection,
 security audit trails,

4 a
security recovery
Encrypt the plaintext = "SECURITY" using Hill Cipher technique.
Key= 7
19
5
8
3
b Briefly define the Caesar Cipher
•
earliest known substitution cipher
•
by Julius Caesar
•
first attested use in military affairs
•
replaces each letter with the letter standing 3 places further down the alphabet
•
example:
5
meet me after the toga party
PHHW PH DIWHU WKH WRJD SDUWB
5 a
With a neat diagram, explain the single round of DES encryption.
10
USN
1 P E
PESIT Bangalore South Campus
Hosur road, 1km before Electronic City, Bengaluru -100
Department of Electronics and Communications
E C
USN
1 P E
E C
PESIT Bangalore South Campus
Hosur road, 1km before Electronic City, Bengaluru -100
Department of Electronics and Communications
b What is the purpose of the S-boxes in DES
5
USN
1 P E
E C
PESIT Bangalore South Campus
Hosur road, 1km before Electronic City, Bengaluru -100
Department of Electronics and Communications
S-Boxes
The S-boxes do the real mixing (confusion). DES uses 8 S-boxes, each with a 6-bit input and a 4-bit
output.
USN
1 P E
E C
PESIT Bangalore South Campus
Hosur road, 1km before Electronic City, Bengaluru -100
Department of Electronics and Communications
6 a
Write the RSA algorithm.
5
1. Pick two distinct primes p and q
2. Compute n = pq and ɸ(n) = (p – 1)(q – 1)
3. Pick e where 1 < e < ɸ(n) and
gcd(e, ɸ(n)) = 1
4. Compute d where
de ≡ 1 (mod ɸ(n))
5. Public key is (n, e), private key is (n, d)
6. Encrypt with C ≡ M e (mod n)
Decrypt with M ≡ C d (mod n)
b Perform the encryption and decryption using RSA algorithm. for the following
5
USN
1 P E
E C
PESIT Bangalore South Campus
Hosur road, 1km before Electronic City, Bengaluru -100
Department of Electronics and Communications
P=17, Q=31, e=7, and M=2.
7 a
Construct a Playfair with the key=largest, Encrypt the following message
5
“must see you over Cadogan West”
b Briefly define the transposition Cipher with examples
•
these hide the message by rearranging the letter order
•
without altering the actual letters used
•
can recognise these since have the same frequency distribution as the original text
•
write message letters out diagonally over a number of rows
•
then read off cipher row by row
Plaintext:
Meet me after the toga party
eg. write message out as:
m e ma t r h t g p r y
e t e f e t e o a a t
•
giving ciphertext
MEMATRHTGPRYETEFETEOAAT
Row transposition Cipher
•
a more complex transposition
•
write letters of message out in rows over a specified number of columns
•
then reorder the columns according to some key before reading off the rows
Key:
4312567
5
USN
1 P E
PESIT Bangalore South Campus
Hosur road, 1km before Electronic City, Bengaluru -100
Department of Electronics and Communications
Plaintext: a t t a c k p
ostpone
duntilt
woamxyz
Ciphertext: TTNAAPTMTSUOAODWCOIXKNLYPETZ
E C