MCQs on Computer Security

DES uses a block size of:

• 56 bits

• 64 bits

• 128 bits

• 32 bits

DES encryption key size is:

• 64 bits with 8 parity bits

• 56 bits of effective key

• Both A and B

• 128 bits

DES operates in how many rounds?

• 8

• 16

• 10

• 20

Which structure is used in DES?

• Substitution-permutation

• Feistel network

• Matrix-based

• Polyalphabetic

The initial and final permutations in DES are:

• Different

• Same

• Inverse of each other

• Random

DES S-boxes are responsible for:

• Key expansion

• Confusion

• Diffusion

• Permutation

The Feistel structure allows:

• Parallel encryption

• Same structure for encryption/decryption

• Asymmetric key usage

• Unlimited key size

DES encryption is considered:

• Very secure today

• Broken by brute-force

• Post-quantum secure

• Only used in email

Triple DES (3DES) applies DES:

• Once

• Twice

• Three times

• Four times

The main weakness of DES is its:

• Key management

• Small key size

• Encryption speed

• Block size