Cryptography Questions and Answers – Overview – IV

This set of Basic Cryptography questions and answers focuses on “Overview”.

1. 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?
a) ci is the ith bit of byte c with value 0x63
b) ci is the ith bit of byte c with value 0x25
c) ci is the ith bit of byte c with value 0x8F
d) ci is the ith bit of byte c with value 0x8A
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2. The inverse s-box permutation follows,
b’i = b(i+2) XOR b(i+5) XOR b(i+7) XOR di
Here di is –
a) di is the ith bit of a byte ‘d’ whose hex value is 0x15
b) di is the ith bit of a byte ‘d’ whose hex value is 0x05
c) di is the ith bit of a byte ‘d’ whose hex value is 0x25
d) di is the ith bit of a byte ‘d’ whose hex value is 0x51
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3. What are the block sizes in the Simplified AES and Full AES algorithms respectively?
a) 8 bits, 64 bits
b) 16 bits, 64 bits
c) 16 bits, 128 bits
d) 32 bits, 128 bits
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4. Which function can be used in AES multiplication –
a) m(x)=x⁷+x⁴+x³
b) m(x)=x⁸+x⁴+x³+x+1
c) m(x)=x⁸+x³+x²+x+1
d) m(x)=x⁸+x⁵+x³+x
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5. In the DES algorithm the Round Input is 32 bits, which is expanded to 48 bits via ______________
a) Scaling of the existing bits
b) Duplication of the existing bits
c) Addition of zeros
d) Addition of ones
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6. Using Differential Crypt-analysis, the minimum computations required to decipher the DES algorithm is-
a) 2⁵⁶
b) 2⁴³
c) 2⁵⁵
d) 2⁴⁷
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7. Using SDES, the Plaintext for the Ciphertext 00001111, given that the key is 1111111111 is,
a) 01100111
b) 00001010
c) 11111111
d) 01101101
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8. 12. For p = 11 and q = 17 and choose e=7. Apply RSA algorithm where Cipher message=11 and thus find the plain text.
a) 88
b) 122
c) 143
d) 111
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9. Reduce the following Big-O notation. O[ ax⁷ + 3 x³ + sin(x)] =
a) O[ax⁷].
b) O[sin(x)].
c) O[x⁷].
d) O[x⁷ + x³].
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10. Reduce the following Big-O notation. O[ eⁿ + an¹⁰] =
a) O[ an¹⁰].
b) O[ n¹⁰ ].
c) O[ eⁿ ].
d) O[ eⁿ+ n¹⁰ ].
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Sanfoundry Global Education & Learning Series – Cryptography and Network Security.

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