Cryptography and network security part a question and answers

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MVIT/ IT DEPT/2019-20-ODD SEM / CNS-PART-A -QA
IT-T73 Cryptography and Network Security
Part- A (Question and Answers) -2019-20 ODD SEM
UNIT-1
1. Define security attack, security mechanism and security services.
Security attack: any action that compromises the security of information owned by an
organization.
Security mechanism: a mechanism that is designed to detect, prevent or recover from a
security attack.
Security services: a service that enhances the security of the data processing systems and the
information transfers of an organization.
2. Define Computer Security.
Ans: Generic name for the collection of tools designed to protect and to thwart hackers.
3. Define Network Security.
Ans: It measures to protect data during their transmission.
4. Define Internet Security.
Ans: It measures to protect data during their transmission over a collection of interconnected
networks.
5. Define Threat.
A potential for violation of security, which exists when there is a circumstance, capability,
action, or event that could breach security and cause harm. That is, a threat is a possible
danger that might exploit a vulnerability.
6. Specify the four categories of security threats.
Interruption Interception
Modification Fabrication
7. Mention the different types of security services.
Authentication
Confidentiality
Data integrity
Non repudiation
Access control
Availability

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8. Define passive attack and active attack.
Passive attacks are in the nature of eavesdropping, or monitoring of transmissions. The types
of passive attack are
1.Release of message content 2.Traffic analysis
Active attacks involve some modification of data stream or creation of a false stream. The
types of active attack are
 Masquerade
 Replay
 Modification
 Denial of service
9. Define integrity and non-repudiation.
Integrity:
Service that ensures that only authorized person able to modify the message.
Non-repudiation:
This service helps to prove that the person who denies the transaction is true or false.
10. Define confidentiality and authentication
Confidentiality: It means how to maintain the secrecy of message. It ensures that the
information in a computer system and transmitted information are accessible only for reading
by authorized person.
Authentication: It helps to prove that the source entity only has involved the transaction
11. Define Attack.
An assault on system security that derives from an intelligent threat; that is, an intelligent act
that is a deliberate attempt to evade security services and violate the security policy of a
system.
12. Define Interruption.
Ans: An asset of the system is destroyed or becomes unavailable or unusable. This is an attack
on availability.
13. Define Interception.
Ans: An unauthorized party gains access to on asset. This is an attack on confidentiality.
Unauthorized party could be a person, a program or a computer.
14. Define Modification.
Ans: An unauthorized party not only gains access to but tampers with an assest. This is an
attack on integrity.
15. Define Fabrication.
Ans: An unauthorized party inserts counterfeit objects in to the system. This is an attack on
authenticity.

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16. Differentiate symmetric and asymmetric encryption?
symmetric : It is a form of cryptosystem in which encryption and decryption performed using
the same key. Eg: DES, AES.
asymmetric : It is a form of cryptosystem in which encryption and decryption Performed using
two keys. Eg:RSA,ECC
17. Define cryptography.
It is a science of writing Secret code using mathematical techniques. The many schemes used
for enciphering constitute the area of study known as cryptography.
18. Define cryptanalysis and cryptology.
Cryptanalysis: techniques used for deciphering or decrypting a message without the
knowledge of the enciphering or encrypting details is said to be cryptanalysis.
Cryptology: the study of cryptography and cryptanalysis together is called cryptology.
19. Define the following terms:
Plaintext: the original message to be transmitted.
Cipher text: the coded (encrypted) message or the scrambled message.
Encryption / Enciphering : process of converting plain text to cipher text.
Decryption/ Deciphering: process of converting cipher text to plain text.
20. What is Brute force attack?
Trying out all the possible keys on a piece of cipher text until an intelligible translation to plain
text is obtained.
21. Mention the various types of cryptanalytic attack.
 Known plaintext
 Cipher text only
 Chosen plaintext
 Chosen Cipher text
22. Define the two basic building blocks of encryption techniques.
Substitution technique – it is one in which the letters of the plaintext are replaced by other
letters or by numbers or symbols.
Transposition technique – it is one which performs some sort of permutation on the plaintext
letters.
23. Mention few mono-alphabetic and poly-alphabetic ciphers.
Mono-alphabetic ciphers: - playfair cipher, hill cipher, Caesar cipher
Poly-alphabetic ciphers: - vigenere cipher, one time pad cipher
24. What is Multiple-letter encryption Cipher?
Ans: Play fair cipher is the best known multiple-letter encryption cipher-which treats diagrams
in the plaintext as single units and translates these units in to cipher text diagrams.

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25. What is auto key system?
Ans: Vigenere cipher method proposed an auto key system, in which a key word is
concatenated, the plaintext itself to provide a running key.
26. What is Rotor Machines?
Ans: Rotor machines are sophisticated pre computer hardware services that use substitution
techniques.
27. What are the two problems with the one time pad?
Ans: i) Making use of large quantities of random keys.
ii) Problem of key distribution and protection.
28. What is steganography? Mention few techniques in it.
Steganography is a technique for hiding the original message. Some of the related techniques
are
 Character marking
 Invisible ink
 Pin punctures
 Typewriter correction ribbon
29. Define stream cipher and block cipher.
A stream cipher is one that encrypts a digital data stream one bit or one byte at a time.
A block cipher is one in which a block of plaintext is treated as a whole and used to produce
a cipher text block of equal block.
30. Why network need security?
When systems are connected through the network, attacks are possible during transmission
time.
31. What are the attacks that can be performed in the networks?
 Disclosure
 Traffic analysis
 Masquerade
 Content modification
 Sequence modification
 Timing modification
 Source repudiation
 Destination repudiation
32. Define Diffusion & confusion.
Diffusion:
It means each plaintext digits affect the values of many cipher text digits which is equivalent
to each cipher text digit is affected by many plaintext digits. It can be achieved by performing
permutation on the data. It is the relationship between the plaintext and cipher text.
Confusion:
It can be achieved by substitution algorithm. It is the relationship between cipher text and
key.

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33. Define Encryption
The process of converting from plaintext to cipher text.
34. Specify the components of encryption algorithm.
(a) Plaintext (b) Encryption algorithm (c) secret key (d) cipher text
(e) Decryption algorithm
35. Differentiate symmetric or private key cryptography and public key or asymmetric
cryptography.
In symmetric key cryptography, only one key is used for encryption and decryption.
In public key cryptography, two keys (public key and private key) are used. When one key is
used for encryption, then the other must be used for decryption. The public key is known to
all the participants but the private key is kept secret by the owner.
36. List the properties of congruence?
Ans: 1) a == b(mod n) if n/(a - b).
2) a == b(mod n) implies b == a(mod n).
3) a == b(mod n) and b == c(mod n) imply a == c(mod n).
37. Write code for Euclidean algorithm?
Ans: EUCLID (a, b)
1) A += a; B += b,
2) if B = 0 return A = gcd (a, b)
3) R =A modB
4) A += B
5) B += R
6) goto 2
38. Define Stream Cipher.
Ans: A stream cipher is one that encrypts a digital data stream one bit or one byte at a time.
39. Define Block Cipher.
Ans: A block cipher is one in which a block of plaintext is treated as a whole and used to
produce a ciphertext block of equal block.
40.Define RC4.
RC4 is a stream cipher designed in 1987 by Ron Rivest for RSA Security. It is a variablekey size
stream cipher with byte-oriented operations.The algorithm is based onthe use of a random
permutation.
Eight to sixteen machine operations are required per output byte, and the cipher can be
expected to run very quickly in software.RC4 is used in the Secure Sockets Layer/Transport
Layer Security (SSL/TLS) standards that have been defined for communication between Web
browsers and servers.

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41.Why not keep the encryption algorithm secret?
We assume that it is impractical to decrypt a message on the basis of the ciphertext plus
knowledge of the encryption/decryption algorithm. This means we do not need to keep the
algorithm secret; we need to keep only the key secret. This feature of symmetric encryption
makes low-cost chip implementations of data encryption algorithms widely available and
incorporated into a number of products. With the use of symmetric encryption, the principal
security problem is maintaining the secrecy of the key.
CNS-UNIT-2
1. Explain conventional encryption?
Conventional encryption
1. The same algorithm with the same key is used for encryption and decryption.
2. The sender and receiver must share the algorithm and the key.
3. The key must be secret
4. It must be impossible or at least impractical message if no other information is available
5. Knowledge of the algorithm plus samples of cipher text must insufficient to determine the
key
2. Explain public key encryption?
1.One algorithm is used for encryption and decryption with a pair of keys, one for encryption
and another for decryption.
2. The sender and receiver must each have one of the matched pair of keys.
3.One of two keys must be kept Secret .
4. It must be impossible or to at least impractical to decipher a message if no other
information is available.
5. Knowledge of the algorithm plus one of key plus samples of ciphertext must be insufficient
to determine the other key.
3. Define Symmetric key Cryptography.
Ans: In symmetric key cryptography, only one key is used for encryption and decryption.
4. Define Public key Cryptography.
Ans: In public key cryptography, two keys (public key and private key) are used. When one
key
is used for encryption, then the other must be used for decryption. The public key is known
to all the participants but the private key is kept secret by the owner.
5. Mention the functions involved in simplified DES.
Ans: i) Initial permutation.
ii) A complex function Fk with a key KI.
iii) Switching.
iv) A complex function Fk with a key K2.
v) Inverse permutation.

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6. Define Multiple Encryption.
It is a technique in which the encryption is used multiple times. Eg: Double DES, Triple DES
7. What is Triple Encryption? How many keys are used in triple encryption?
Triple Encryption is a technique in which encryption algorithm is performed three times
using three keys.
8. Give the five modes of operation of Block cipher.
 Electronic Codebook(ECB)
 Cipher Block Chaining(CBC)
 Cipher Feedback(CFB)
 Output Feedback(OFB)
 Counter(CTR)
9. Explain Avalanche effect.
A desirable property of any encryption algorithm is that a small change in either the plaintext
or the key produce a significant change in the cipher text.
In particular, a change in one bit of the plaintext or one bit of the key should produce a change
in many bits of the cipher text. If the change is small, this might provider a way to reduce the
size of the plaintext or key space to be searched.
10. What is AES?
Ans: Advanced encryption standard is a block cipher intended to replace DES for commercial
applications. It uses a 12~-bit block size and a key size of 128, 192 or 256 bits.
11. What are the characteristics of AES Cipher?
• Resistance against all known attacks.
• Speed and code compactness on a wide range of platform.
• Design simplicity.
12. List four different stages of AES?
1) Substitute bytes 2) Shift rows 3) Mix columns 4) Add Round key.
13. List the evaluation criteria defined by NIST for AES?
The evaluation criteria for AES is as follows:
 Security
 Cost
 Algorithm and implementation characteristics
14. What is sub bytes?
The forward substitute byte transformation, called Sub Bytes, is a simple table lookup.
15. What is Inv Shift Rows?
The inverse shift row transformation, called Inv Shift Rows, performs the circular shifts in
the opposite direction for each of the last three rows, with a one byte circular shift for the
second row and so on.

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16. What is Mix Columns?
The forward "mix" column transformation, called Mix columns, operates on each column
individual.
17. What is Add Round Key?
In the forward add round key transformation, called Add Round Key, the 128 bits of state
are bitwise XORed with the 128 bits of the round key.
18. Define Fermat Theorem?
Fermat Theorem states the following: If p is prime and a is a positive integer not divisible by
p, then Ap-1=1 mod p
19. Define Euler’s theorem and it’s application?
Euler’s theorem states that for every a and n that are relatively prime:
aΦ(n) =1 mod n
20. Define Euler’s totient function or phi function and their applications?
The Euler’s totient function states that, it should be clear for a prime number p,
Φ(p) =p-1
21. Describe in general terms an efficient procedure for picking a prime number?
The procedure for picking a prime number is as follows:
1. Pick an odd integer n at random (eg., using a pseudorandom number generator).
2. Pick an integer a<n at random.
3. Perform the probabilistic primality test, such as Miller-Rabin. If n fails the test, reject the
value n and go to step 1.
4. If n has passed a sufficient number of tests, accept n; otherwise , go to step 2.
22. Define the meaning of relatively prime (or) co-prime?
Two integer a and b are relatively prime if gcd(a,b) = 1
Eg: gcd(20,7) = gcd(7,20 mod 7)
= gcd(7,6)
= gcd(6,7 mod 6)
= gcd(1,6 mod 1)
= gcd(1,0)
= 1
23. Define prime number and Divisibility?
Prime Number:
An integer p>1 is a prime number if and only if its divisor are ±1 &± p
Eg: p= 13 then divisors are ±1 and ±3
Any integer a>1 can be factored in a way as a = p1
a1,p2
a2,….pt
at where p1<p2
… pt ,ai are prime numbers, a’ is a +ive integer then it can be written as a = Πp
ap. P Є p ; whereap> 0 . p represents set of prime numbers.

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24. Define Euler’s totient function
The Euler’s totient function states that, it should be clear for a prime number p,
Φ (p)= p-1
25. Determine Φ (27) using Euler’s totient function?
Φ (p e)=p e-p e-1
Φ (3 3)=3 3- 3 2
=27-9
=18
Φ (27)=18
26. Find gcd (1970, 1066) using Euclid’s algorithm?
gcd (1970,1066) = gcd(1066,1970 mod 1066)
= gcd(1066,904)
= 2
27. What is the primitive root of a number?
We can define a primitive root of a number p as one whose powers generate all the integers
from 1 to p-1. That is p, if a is a primitive root of the prime number p then the numbers.
28. Determine the gcd (24140,16762) using Euclid’s algorithm.
Soln: We know, gcd(a, b) = gcd(b, a mod b)
gcd(24140,16762) =gcd(16762,7378)
gcd(7378,2006) =gcd(2006,1360)
gcd(1360,646) =gcd(646,68)
gcd(68,34) = 34
gcd(24140,16762) = 34.
29. Perform encryption and decryption using RSA Alg. for the following. P=7; q=11; e=17;
M=8.
Soln: n = pq
n = 7*11=77
Φ(n)=(p-1) (q-1)
=6*10 = 60
e =17 d =27
C = Me mod n
C = 817 mod 77
= 57
M = Cd mod n
= 5727 mod 77 = 8
30. What is the primitive root of a number?
We can define a primitive root of a number p as one whose powers generate allthe integers
from 1 to p-1. That is p, if a is a primitive root of the prime number p thenthe numbers.

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31. Define Euler’s totient function (used in RSA algorithm).
It is the number of positive integers that are less than ‘n’ and relatively
prime to ‘n’.
Where n is the product of two prime numbers (p & q)
It is represented as F(n) and it is expressed as F(n) = F(pq) = (p-1)(q-1).
32. Define Factoring Problem.
Ans: Mathematical approach takes 3 forms:
• Factor n = p * q, hence find <j>(n) and then d.
• Determine <j>(n) directly without determiningp and q and find d.
• Find d directly, without first determination <j>(n).
33. Define RSA
The Rivest-Shamir-Adleman (RSA) scheme has the most widely accepted and implemented
general-purpose approach to public-key encryption. The RSA scheme is a block cipher in
which the plaintext and ciphertext are integers between 0 and n - 1 for some n. A typical size
for n is 1024 bits, or 309 decimal digits. That is, n is less than 2 power 1024.
34. What are the various approaches to attacks the RSA algorithm?
Ans: i) Brute force attack.
ii) Mathematical attacks.
iii) Timing attacks.
35. Define Timing Attacks.
The opponent can determine a private key by keeping track of how long a computer takes to
decipher messages. Although the timing attack is a serious threat, there are simple counter
measures that can be used:
• Constant Exponentiation Time
• Random Delay
• Blinding.
36. What are roles of public and private key?
The two keys used for public-key encryption are referred to as the public key and the private
key. The private key is kept secret and the public key is known publicly. Usually the public key
is used for encryption purpose and the private key is used in the decryption side.
37. Specify the applications of the public key cryptosystem?
The applications of the public-key cryptosystem can classified as follows
Encryption/Decryption: The sender encrypts a message with the recipient’s public key.
Digital signature: The sender “signs” a message with its private key. Signing is achieved by a
cryptographic algorithm applied to a message or to a small block of data that is a function of
the message.
Key Exchange: Two sides cooperate to exchange a session key. Several different approaches
are possible, involving the private key(s) of one or both parties

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CNS-UNIT-3
1. What is Discrete Logarithms?
Ans: For any integer b and a primitive root a of prime number p, the unique exponent.
'i' is referred as discrete logarithm of the number b for the base a(mod P).
dlog (b) obtained from a,p
b = d(modp) where 0 ~ i~ (p - 1).
2. What is a one way function?
One way function is one that map the domain into a range such that every function value
has a unique inverse with a condition that the calculation of the function is easy where as
the calculations of the inverse is infeasible.
3. What is a trapdoor one way function?
It is function which is easy to calculate in one direction and infeasible to calculate in other
direction in the other direction unless certain additional information is known. With the
additional information the inverse can be calculated in polynomial time. It can be
summarized as: A trapdoor one way function is a family of invertible functions fk, such
that Y= fk( X) easy, if k and X are known
X=fk-1(Y) easy, if k and y are known
X= fk-1(Y) infeasible, if Y is known but k is not known
4. Why do we need Diffie Hellman algorithm?
It is used for exchanging the secret keys between the sender and the receiver. It allows two
users to exchange a key securely.
User A and B exchange the key using Diffie-Hellman algorithm. Assume α=5
q=11 XA=2 XB=3. Find the value of YA,YB and k?
Soln:
YA= αX
A mod q
= 25 mod 11
= 3
YB = αX
B mod q
= 125 mod 11
= 4
K = ( YA) X
B mod q
= 27 mod 11
= 5
K = ( YB) X
A mod q
= 16 mod 11
= 5

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5. Mention the various ways of producing an authenticator. (Or) Define the classes of
message authentication function.
Message encryption: The entire cipher text would be used for authentication.
Message Authentication Code: It is a function of message and secret key produce a fixed
length value.
Hash function: Some function that map a message of any length to fixed length which serves
as authentication.
6. Define one way property, weak collision resistance and strong collisionresistance of
hash function.
For any given value h, it is computationally infeasible to find x such that
H(x) = h – one way property.
For any given block x, it is computationally infeasible to find y ≠ x with
H(y) = H(x) – weak collision resistance.
It is computationally infeasible to find any pair (x, y) such that
H(x) =H(y) – strong collision property.
7. What is message authentication?
It is a procedure that verifies whether the received message comes from assigned source has
not been altered. It uses message authentication codes, hash algorithms to authenticate
the message.
8. What are the requirements for message authentication?
The requirements for message authentication are
i. Disclosure: Release of message contents to any person or process not processing the
appropriate cryptographic key
ii. Traffic Analysis: Discovery of the pattern of traffic between parties. In a connection
oriented application, the frequency and duration of connections could be determined. In
either a connection oriented or connectionless environment, the number and length of
messages between parties could be determined.
Masquerade: Insertion of messages into the network from a fraudulent source. This includes
the creation of messages by an opponent that are purported to come from an authorized
entity. Also included are fraudulent acknowledgements of message receipt or no receipt
by someone other than the message recipient.
iv. Content modification: Changes to the contents of a message , including insertion,
deletion, transposition, and modification.
v. Sequence modification: Any modification to a sequence of messages between parties,
including insertion, deletion, and modification.
vi. Timing modification: Delay or replay of messages. In a connection oriented application,
an entire session or sequence of messages could be a replay of some previous valid
session, or individual messages in the sequence could be delayed or replayed. In
connectionless application, an individual message could be delayed or replayed.
vii. Source repudiation: Denial of transmission of message by source.
viii. Destination repudiation: Denial of receipt of message by destination.

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9. What you meant by hash function?
Hash function accept a variable size message M as input and produces a fixed size hash code
H(M) called as message digest as output. It is the variation on the message authentication
code.
10. Differentiate MAC and Hash function?
MAC: In Message Authentication Code, the secret key shared by sender and receiver. The
MAC is appended to the message at the source at a time which the message is assumed
or known to be correct.
Hash Function: The hash value is appended to the message at the source at time when the
message is assumed or known to be correct. The hash function itself not considered to be
secret.
11. Any three hash algorithm.
• MD5 (Message Digest version 5) algorithm.
•SHA_1 (Secure Hash Algorithm).
• RIPEMD_160 algorithm.
12. What are the requirements of the hash function?
• H can be applied to a block of data of any size.
• H produces a fixed length output.
• H(x) is relatively easy to compute for any given x, making both hardware and software
implementations practical.
13. What you meant by MAC?
MAC is Message Authentication Code. It is a function of message and secret key which
produce a fixed length value called as MAC. MAC = Ck(M)
Where M = variable length message
K = secret key shared by sender and receiver.
CK(M) = fixed length authenticator.
14. What is weak collision resistance?
Ans:For any given block x, it is computationally infeasible to find y # x such that H(y) = H(x).it
is referred to as weak collision resistance. It is proportional to 2n
15. What is strong collision resistance?
Ans: It is computation ally infeasible to find anypair (x, y) such that H(x) = H(y). This is
sometimes referred to as strong collision resistance. It is proportional to 2n/2
16. What are the three desirable properties of Hash functions?
Ans: One-way
Weak collision resistance
Strong collision resistance.

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17. List the steps of secure Hash algorithm?
Ans: - Append padding bits.
- Append length.
- Initialize hash buffer .
- Process message in l024-bit (128-word) blocks.
- Output.
18. What are the two compression function used in secure hash algorithm?
Ans: A function specifically designed for the hash function or a symmetric block cipher.
19. What are the two categories of message authentication codes?
Ans: - Based on the use of secure hash algorithm.
- Based on the use of symmetric block cipher.
20. Differentiate internal and external error control.
Internal error control: an error detecting code also known as frame check sequence or
checksum.
External error control: error detecting codes are appended after encryption.
21. What is the meet in the middle attack?
This is the cryptanalytic attack that attempts to find the value in each of the range and
domain of the composition of two functions such that the forward mapping of one
through the first function is the same as the inverse image of the other through the second
function-quite literally meeting in the middle of the composed function.
22. What is the role of compression function in hash function?
The hash algorithm involves repeated use of a compression function f, that takes two inputs
and produce a n-bit output. At the start of hashing the chaining variable has an initial value
that is specified as part of the algorithm. The final value of the chaining variable is the
hash value usually b>n; hence the term compression.

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23. Define digital signature.
A digital signature is an authentication mechanism that enables the creator of a message
to attach a code that acts as a signature. Typically the signature is formed by taking the
hash of the message and encrypting the message with the creator’s private key. The
signature guarantees the source and integrity of the message
Digital signatures are used in e-commerce, software distribution, financial transactions
and other situations that rely on forgery or tampering detection techniques. A digital
signature is also known as an electronic signature.
24. Distinguish between direct and arbitrated digital signature?
Direct:
1.The direct digital signature involves only the communicating parties.
2.This may be formed by encrypting the entire message with the sender’s private key.
Arbitrated digital signature:
1.The arbiter plays a sensitive and crucial role in this digital signature.
2. Every signed message from a sender x to a receiver y goes first to an arbiter A, who subjects
the message and its signature to a number of tests to check its origin and content.
25. What are the properties a digital signature should have?
It must verify the author and the data and time of signature.
It must authenticate the contents at the time of signature.
It must be verifiable by third parties to resolve disputes.
26. What requirements should a digital signature scheme should satisfy?
The signature must be bit pattern that depends on the message being signed.
The signature must use some information unique to the sender, to prevent both forgery and
denial.
It must be relatively easy to produce the digital signature.
It must be relatively easy to recognize and verify the digital signature.
It must be computationally infeasible to forge a digital signature, either by constructing new
message for an existing digital signature or by constructing a fraudulent digital signature
for a given message.
It must be practical to retain a copy of the digital signature in storage.

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CNS- UNIT-4
1. List out the different techniques of distributing the public key.
 Public announcement
 Publicly available directory
 Public key authority
 Public key certificate
2. What is the purpose of X.509 standard?
X.509 defines framework for authentication services by the X.500 directory to its users.X.509
defines authentication protocols based on public key certificates.
3. What you mean by Verisign certificate?
Mostly used issue X.509 certificate with the product name” Verisign digital id”. Each digital id
contains owner’s public key, owner’s name and serial number of the digital id.
4. How E-mail compatibility is performed?
Radix-64 is the technique which is used for E-mail compatibility. InRadix-64, each group of 3
octets of binary data is mapped into 4 ASCII characters.
5. Mention the services provided by the Pretty Good Privacy (PGP).
a. Authentication
b. Confidentiality
c. Compression
d. E-mail compatibility
e. Segmentation and reassembly
7. Signature is generated before compression in PGP. Why?
There are two reasons behind it.
1. It is preferable to sign an uncompressed message so that one can storeonly the
uncompressed message together with the signature for futureverification. If one signed a
compressed document, then it would benecessary either to store a compressed version of
the message for laterverification or to recompress the message when verification is required.
2. Even if one were willing to generate dynamically a recompressed message for verification,
PGP’s compression algorithm presents a difficulty. Thealgorithm is not deterministic.
8. Why E-mail compatibility function in PGP needed?
Electronic mail systems only permit the use of blocks consisting of ASCII text. To
accommodate this restriction PGP provides the service converting the row 8-bit binary stream
to a stream of printable ASCII characters. The scheme used for this purpose is Radix-64
conversion.
9. Name any cryptographic keys used in PGP?
 One-time session conventional keys.
 Public keys.
 Private keys.
 Pass phrase based conventional keys.

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10. Define key Identifier?
PGP assigns a key ID to each public key that is very high probability unique with a user ID. It is
also required for the PGP digital signature. The key ID associated with each public key consists
of its least significant 64bits.
11. Explain the reasons for using PGP?
It is available free worldwide versions that run on a variety of platforms, including
DOS/Windows, UNIX, macintosh and many more.
It is based on algorithm that have survived extensive public review and are considered
extremely secure (eg.) RSA, DSS.
It has a wide range of applicability from corporations that wish to select and enforce a
standardized scheme for encrypting files and communication.
It was not developed by nor is it controlled by any government or standards organization.
12. What is the need of public key ring and private key ring?
Public key ring is one of the data structures which is used to store thepublic keys of the other
participants.
Private Key ring is a data structure which is used to store the public andthe private keys of the
owner alone.
13. Mention the benefits of IPSec.
a. It provides strong security that can be applied to all traffic crossing theperimeter.
b. IPSec in a firewall is resistant to bypass.
c. IPSec is below the transport layer and so is transparent to applications.
d. IPSec is transparent to users.
13. List out the services provided by the IPSec.
 Access control
 Connectionless integrity
 Data origin authentication
 Rejection of replayed packets
 Confidentiality
 Limited traffic flow confidentiality
14. What are the function areas of IP security?
• Authentication
• Confidentiality
• Key management.
15. Give the application of IP security?
• Provide secure communication across private & public LAN.
• Secure remote access over the Internet.
• Secure communication to other organization.
16. What are the protocols used to provide IP security?
• Authentication header (AH) protocol.
• Encapsulating Security Payload (ESP) protocol.

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17. General format of IPsec ESP Format?
Security Parameter Index(SPI)
Sequence Number(SN)
Payload Data (Variable)
Padding(0-255 bytes)
Authentication Data (variable)
18. What is Authentication Header? Give the format of the IPsec Authentication
Header?
It provides the authentication of IP Packet, so authentication is based on the use of MAC.
List the steps involved in SSL record protocol?
1. SSL record protocol takes application data as input and fragments it.
2. Apply lossless Compression algorithm.
3. Compute MAC for compressed data.
4. MAC and compression message is encrypted using conventional alg
19. Define transport and tunnel mode.
i. Transport mode provides protection primarily for upper layerprotocols. Transport mode
protection extends to the payload of anIP packet. Transport mode is used for end-to-end
communicationbetween two hosts.
ii. Tunnel mode provides protection to the entire packet. The entire packet (original packet)
plus security fields is treated as thepayload of new outer IP packet with a new outer IP header.
Herethe packet travels through a tunnel from one point of an IP networkto another.
19. Why do we need an anti replay service?
Anti replay service is required in order to avoid the duplicatepackets (created by the
opponent) which may cause disruption inthe service.
21. What is the need pf padding in Encapsulating Security Payload (ESP)?
a. If an encryption algorithm requires the plaintext to be a multiple of somenumber of bytes,
the padding field is used to expand the plaintext to therequired length.
b. ESP format requires that the pad length and the next header fields be rightaligned within a
32-bit word. The padding field is used to assure thisalignment.
c. Additional padding may be added to provide partial traffic flowconfidentiality by concealing
the actual length of the payload.
22. How the security associations be combined?
It can be done in two ways: 1.Transport adjacency 2. Iterated tunneling
23. What are the headers fields define in MIME?
• MIME version.
• Content type.
• Content transfer encoding.
• Content id.
• Content description.

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24. What are the key algorithms used in S/MIME?
• Digital signature standards.
• Diffi Hellman.
• RSA algorithm.
25. What are the different between SSL version 3 and TLS?
• In SSL the minor version is 0 and * In TLS, the major version is 3 and thethe major version is
3 minor version is 1.
* SSL use HMAC alg., except that * TLS makes use of the same alg.the padding
bytesconcatenation.
* SSL supports 12 various alert * TLS supports all of the alert codes. Codesdefined in SSL3 with
the exception of• no _ certificate.
27. List the step involved in SSL required protocol?
Ans: - It takes application data as input and fragments it.
- Apply loss less compression algorithm.
- Compute MAC for compound data.
- MAC and compression message is encrypted using conventional algorithm.

20
CNS- Unit-5
1. What are the 802.11 RSN Security Specification?
Authentication: A protocol is used to define an exchange between a user and an AS that
provides mutual authentication and generates temporary keys to be used between the client
and the AP over the wireless link.
Access control:1 This function enforces the use of the authentication function, routes the
messages properly, and facilitates key exchange. It can work with a variety of authentication
protocols.
Privacy with message integrity: MAC-level data (e.g., an LLC PDU) are encrypted along with
a message integrity code that ensures that the data have not been altered.
2. What are the five 802.11 phase of operation.
 Discovery,
 Authentication,
 Key generation and distribution
 Protected data transfer,
 Connection termination.
3. Define PSK and MSK.
PAIRWISE KEYS Pairwise keys are used for communication between a pair of devices, typically
between an STA and an AP. These keys form a hierarchy beginning with a master key from
which other keys are derived dynamically and used for a limited period of time. At the top
level of the hierarchy are two possibilities. A pre-shared key (PSK) is a secret key shared by
the AP and a STA and installed in some fashion outside the scope of IEEE 802.11i. The other
alternative is the master session key (MSK), also known as the AAAK, which is generated using
the IEEE 802.1X protocol during the authentication phase.
4. Explain group key distribution.
GROUP KEY DISTRIBUTION:For group key distribution, the AP generates a GTK and distributes
it to each STA in a multicast group.The two-message exchange with each STA consists of the
following:
AP STA: This message includes the GTK, encrypted either with RC4 or with AES.The
key used for encryption is KEK. A MIC value is appended.
STA AP: The STA acknowledges receipt of the GTK. This message includes a MIC
value.

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5. What are two service provided by TKIP?
TKIP is designed to require only software changes to devices that are implemented with the
older wireless LAN security approach called Wired Equivalent Privacy (WEP). TKIP provides
two services:
Message integrity: TKIP adds a message integrity code (MIC) to the 802.11 MAC frame after
the data field. The MIC is generated by an algorithm, called Michael, that computes a 64-bit
value using as input the source and destination MAC address values and the Data field, plus
key material.
Data confidentiality: Data confidentiality is provided by encrypting the MPDU plus MIC value
using RC4.
6. Define WAP.
The Wireless Application Protocol (WAP) is a universal, open standard developed by the WAP
Forum to provide mobile users of wireless phones and other wireless terminals such as pagers
and personal digital assistants (PDAs) access to telephony and information services, including
the Internet and the Web. WAP is designed to work with all wireless network technologies
(e.g., GSM, CDMA, and TDMA). WAP is based on existing Internet standards, such as IP, XML,
HTML, and HTTP, as much as possible. It also includes security facilities. At the time of this
writing, the current release of the WAP specification is version 2.0.
7. List the WAP specification.
The WAP specification includes:
• A programming model based on the WWW Programming Model
• A markup language, the Wireless Markup Language, adhering to XML
• A specification of a small browser suitable for a mobile, wireless terminal
• A lightweight communications protocol stack
• A framework for wireless telephony applications (WTAs)
8. Define wireless markup language.
WML was designed to describe content and format for presenting data on devices with
limited bandwidth, limited screen size, and limited user input capability. It is designed to work
with telephone keypads, styluses, and other input devices common to mobile, wireless
communication. WML permits the scaling of displays for use on two-line screens found in
some small devices, as well as the larger screens found on smart phones.
9. List the important feature of WML.
Important features of WML include:
• Text and image support: Formatting and layout commands are provided for text and
limited image capability.
• Deck/card organizational metaphor: WML documents are subdivided into small, well-
defined units of user interaction called cards. Users navigate by moving back and forth
between cards. A card specifies one or more units of interaction (a menu, a screen of text,

22
or a text-entry field). A WML deck is similar to an HTML page in that it is identified by a
Web address (URL) and is the unit of content transmission.
• Support for navigation among cards and decks: WML includes provisions for event
handling, which is used for navigation or executing scripts.
10. Explain WTA.
Wireless telephony applications (WTA): A collection of telephony-specific extensions for call
and feature control mechanisms that provide authors advanced mobile network services.
Using WTA, applications developers can use the micro browser to originate telephone calls
and to respond to events from the telephone network.
11. Define WTLS.
WTLS provides security services between the mobile device (client) and the WAP gateway.
WTLS is based on the industry-standard Transport Layer Security (TLS) Protocol, 3 which is a
refinement of the Secure Sockets Layer (SSL) protocol. TLS is the standard security protocol
used between Web browsers and Web servers. WTLS is more efficient that TLS, requiring
fewer message exchanges.
12. List the Features of WTLS.
WTLS provides the following features.
• Data integrity: Uses message authentication to ensure that data sent between the client
and the gateway are not modified.
• Privacy: Uses encryption to ensure that the data cannot be read by a third party.
• Authentication: Uses digital certificates to authenticate the two parties.
• Denial-of-service protection: Detects and rejects messages that are replayed or not
successfully verified.
13. Define three transaction classes of WTP.
WTP provides three transaction classes that may be invoked by WSP or another higher layer
protocol:
• Class 0: Unreliable invoke message with no result message
• Class 1: Reliable invoke message with no result message
• Class 2: Unreliable invoke message with one reliable result message
14. Mention the phases of the Handshake protocol.
a. Phase 1 – establish security capabilities
b. Phase 2 – server authentication and key exchange
c. Phase 3 – client authentication and key exchange
d. Phase 4 – finish
15. Draw the WTLS protocol stack.

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