If all letters have the same chance of being chosen, the IC is approximately

CRYPTOGRAPHY AND NETWORK SECURITY - ENCRYPTION TECHNIQUES MCQ

• In brute force attack, on average half of all possible keys must be tried to achieve success
• If the sender and receiver use different keys, the system is referred to as conventional cipher system
• Divide (HAPPY)26 by (SAD)26. We get quotient –
• Dividing (11001001) by (100111) gives remainder –
• pi in terms of base 26 is
• The time required to convert a k-bit integer to its representation in the base 10 in terms of big-O notation is
• In base 26, multiplication of YES by NO gives –
• Division of (131B6C3) base 16 by (lA2F) base 16 yeilds –
• An encryption scheme is unconditionally secure if the ciphertext generated does not contain enough information to determine uniquely the corresponding plaintext, no matter how much cipher text is available
• The estimated computations required to crack a password of 6 characters from the 26 letter alphabet is-
• Use Caesar’s Cipher to decipher the following: HQFUBSWHG WHAW
• Caesar Cipher is an example of
• Monoalphabetic ciphers are stronger than Polyalphabetic ciphers because frequency analysis is tougher on the former
• Which are the most frequently found letters in the English language ?
• Choose from among the following cipher systems, from best to the worst, with respect to ease of decryption using frequency analysis
• On Encrypting “thepepsiisintherefrigerator” using Vignere Cipher System using the keyword “HUMOR” we get cipher text-
• On Encrypting “cryptography” using Vignere Cipher System using the keyword “LUCKY” we get cipher text
• The Index of Coincidence for English language is approximately
• If all letters have the same chance of being chosen, the IC is approximately
• Consider the cipher text message with relative frequencies:
• Consider the cipher text message:
• A symmetric cipher system has an IC of 0.041. What is the length of the key ‘m’?
• In public key cryptosystem _____ keys are used for encryption and decryption
• In public key cryptosystem which is kept as public?
• In a trapdoor function, the functions are easy to go in
• Pretty good privacy program is used for
• PGP system uses
• Private key algorithm is used for _____ encryption and public key algorithm is used for _____ encryption
• Which are called the block ciphers?
• Which has a key length of 128 bits?
• Which algorithm can be used to sign a message?
• Examples of hash functions are
• A cryptographic hash function has variable output length
• A set of numbers is called as super increasing if
• Knapsack problem can be solved by
• Merkle hellman is a symmetric cryptosystem
• In Merkle Hellman method same key is used for encryption and decryption
• Cipher system can be solved effectively by statistically using
• Encryption transformations are known as
• For n input bits the number of substitution patterns are
• In transposition, the plaintext letters are
• The substitution of the letters are done
• In cipher feedback method, encryption is done on
• In stream encryption, the key sequence repeats itself
• In which method, key-stream is generated independently?
• Synchronous ciphers uses
• Public key cryptosystem uses same key for both encryption and decryption
• Which should be kept as a secret in public key cryptosystem?
• Public key cryptosystem is also known as
• Euler’s totient function is determined by
• Pretty good privacy (PGP) security system uses
• Public key cryptosystem is used for the encryption of
• For digital signatures private key cryptosystem is used
• Data compression includes
• PGP offers _____ block ciphers for message encryption
• Which block cipher has key length of 128 bits?
• These three ciphers can operate of ______ of plaintext and cipher text
• The key size of DES is
• Which operation is used in encryption using IDEA?
• What is the key size allowed in PGP?
• Which algorithm is used for public key encryption?
• Which should be used first to decrypt?
• The digital signature provides authentication to the
• In hash function output length is fixed
• The hash function
• DSA protocol is based on

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