Q. In Elgamal cryptosystem, given the prime p=31.
What is the respective plaintext character for C = (27, 20)?

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Q. The multiplicative Inverse of 550 mod 1769 is –

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Q. It is desirable to revoke a certificate before it expires because –

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Q. Suppose that A has obtained a certificate from certification authority X1 and B has obtained certificate authority from CA X2. A can use a chain of certificates to obtain B’s public key. In notation of X.509, the correct order of this chain is represented as –

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Q. A total of seven messages are required in the Public-Key distribution scenario. However, the initial five messages need to be used only infrequently because both A and B can save the other’s public key for future – a technique known as ____________

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Q. Which of the following statements are true?

i) In the CBC mode, the plaintext block is XORed with previous ciphertext block before encryption.
ii) The CTR mode does not require an Initialization Vector
iii) The last block in the CBC mode uses an Initialization Vector
iv) In CBC mode repetitions in plaintext do not show up in ciphertext

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Q. The blowfish algorithm’s key expansion converts a key of at most 448 bits into several subkey arrays totaling ___ bytes.

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Q. Which of the following statements are true with respect to the blowfish algorithm?

i) Provided key is large enough, brute-force key search is not practical, especially given the high key schedule cost
ii) Key dependent S-boxes and sub keys make analysis very difficult
iii) Changing both halves in each round increases security
iv) Blowfish has improved avalanche effects

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Q. The last two blocks of the XTS-AES mode are

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Q. How many keys are used in the ANSI X9.17 PRNG?

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Q. Maurer’s Universal Statistical Test is

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Q. On Encrypting “thepepsiisintherefrigerator” using Vignere Cipher System using the keyword “HUMOR” we get cipher text

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Q. Consider the cipher text message:

YJIHX RVHKK KSKHK IQQEV IFLRK QUZVA EVFYZ RVFBX UKGBP KYVVB QTAJK TGBQO ISGHU CWIKX QUXIH DUGIU LMWKG CHXJV WEKIH HEHGR EXXSF DMIIL UPSLW UPSLW AJKTR WTOWP IVXBW NPTGW EKBYU SBQWS

Relative Frequencies
3 7 2 2 5 5 7 9 11 4 14 4 2 1 3 4 6 5 6 5 7 10 9 8 4 2

The Index of Coincidence is

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Q. The plain text for the cipher text RRLMWBKASPDH. Given the encryption key
[(17 17 5 | 21 18 21 | 2 2 19)] is –

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Q. The Inverse S-box value for byte stored in cell (D,2)

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Q. Division of (131B6C3) base 16 by (lA2F) base 16 yeilds

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Q. In AES, to make the s-box, we apply the transformation –

b’i = bi XOR b(i+4) XOR b(i+5) XOR b(i+6) XOR b(i+7) XOR ci
What is ci in this transformation?

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Q. The inverse s-box permutation follows -

b’i = b(i+2) XOR b(i+5) XOR b(i+7) XOR di
Here di is –

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Q. In the DES algorithm the Round Input is 32 bits, which is expanded to 48 bits via ______________

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Q. Using Differential Crypt-analysis, the minimum computations required to decipher the DES algorithm is-

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