Classical Cryptography

1. An example of a monoalphabetic cipher is:

• Shiftcipher
• Hill cipher
• Vigenere cipher

2. Two conditions must hold to find the multiplicative inverse of an integer modulo another integer:

• The gcd of the integer and the modulo integer must be invertible
• The gcd of the integer and the modulo integer must be equal to one
• The gcd of the integer and the modulo integer must be equal to zero

3. The main purpose of using a poly alphabetic cipher is to:

• Hide the statistical property of the plaintext letters
• Increase the number of letters in the ciphertext
• Defeat brute force attack

4. Hill cipheris:

• An Asymmetric cipher
• A Symmetric cipher
• A Hash function

5. Cyptography can be directly linked to all of these core security properties except:

• Confidentiality
• Integrity
• Availability
• Authenticity

Symmetric Cryptography

1. The basic elements of a sound cryptography are:

• Diffusion, Key secrecy and Confusion
• Encryption, Key secrecy and confusion
• Encryption, decryption and keysecrecy

2. In a blockcipher:

• Messages are encryptedat once
• Messages are split into blocks before encryption
• Messages are split into two before encryption

3. Symmetric encryption can provide:

• Non-repudiation
• Confidentiality

4. The following are challenges with symmetric encryption except:

• Key distribution
• Key management
• Speed of execution

5. In stream ciphers:

• Successive keys are used to encrypt plaintext message
• The same key is used to encrypt plaintext message

6. The security of cryptography must rely on:

• Keeping the cryptography algorithm secret
• Keeping both the crypto algorithm and the key secret
• Keeping only the key secret

Asymmetric Cryptography

1. Asymmetric cryptography uses:

• Public and private keys
• A secret key known to two parties
• Public keys

2. The security level of 128-bit asymmetrickey is the same as 128-bit symmetric key:

• True
• False

3. The security of RSA is based on the difficulty of:

• Solving the logarithm problem
• Factoring large prime numbers
• Solving quadratic problem

4. A 4-bit (11012) messagein an Elliptic curve can be expressed in polynomial form as:

• x^4+x^2+1
• x^3+x^2+x+1
• x^3+x^2+1

Hashing and Digital Signature

1. In digital signature:

• The publickeyis used to signthemessageand theprivate keyused to verifythesignature
• The publickeyis used to encryptthemessageand theprivate keyis used to decryptit
• The private keyis used to signthemessageand thepublickeyto verify

2. Hash functions should be collision resistant because:

• Authentication can only be achieved if there is no collision
• Integrity can only be preserved if there is no collision
• Confidentiality can only be achieved if there is no collision

3. MAC

• Uses asymmetric keys and provide authentication and integrity
• Uses symmetric key and provide authentication and integrity
• Uses symmetric key and provide authentication, integrity and non-repudiation

4. One-wayness of a hash function means

• Two different messages cannot hash to the same hash values
• One message cannot produce two different hash values
• It is not possible to derive the input from the hash output

5. Which hash function has collision been found?

• SHAE256
• MD5
• RIPEMDE160

6. What is the major difference between MAC and Hashing

• MAC provides integrity
• MAC provides authentication
• MAC provides confidentiality

7. Whatis themajor differencebetweenMAC and digital signature

• MAC hashes the message and encrypt with the private key
• MAC hashes the message and the symmetric key
• MAC hashes the message

8. Why do we need to hash in digital signature?

• Because we need irreversible function
• Because of speed and size
• To avoid message collisions

Public Key Infrastructure and Overview of crypto in Blockchain

1. What does PKI achieve in publickey systems? (multiple answers)

• Binds an identity to a publickey
• Verifies users transactions
• Provides key management such as key distribution, validation and revocation

2. How is PGP certificate different from X.509 certificatemodel? (multiple answers)

• You can create your own certificate
• You need a single authority to sign your certificate
• A PGP certificate can contain multiple signatures

3. PGP uses:

• Symmetric and asymmetric crypto systems
• Only symmetric
• Only asymmetric