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804 Appendix • Self Test Appendix

Answers A and C.These are characteristics of the 3DES algorithm.Answer B. 3DES is a sym-
metric algorithm and all symmetric algorithms are vulnerable to brute-force attacks. Consider
the brute-force attack theoretical in this case, as it is computationally infeasible to do so.
Answer D. 3DES cannot be broken in any reasonable time frame with today’s computers,
regardless of the computational power available. However, DES (the single version) can be theo-
retically broken in hours using specialized hardware.

2. What is the purpose of a hash algorithm? (Select all that apply)
A. To encrypt e-mail.
B. To encrypt short phrases in a one-way fashion.
C. To create a secure checksum.
D. To obscure an identity.
Answers B and C. Hash algorithms are one-way, irreversible functions that are suitable for
encrypting passwords or calculating secure checksums.
Answer A.You might sign an e-mail using a hashing algorithm, but you would not encrypt and
e-mail, since by definition there is no way to decrypt a hash.Answer D.This is a nonsense
answer.

3. Widgets GmbH is a German defense contractor.What algorithms are they most likely to use to
secure their VPN connections? (Choose all that apply).
A. 3DES
B. El Gamal
C. AES
D. IDEA
Answers C and D. Because Widgets GmbH is a defense contractor, they may be less likely to
choose encryption developed entirely in the U.S.They would most likely use the IDEA algo-
rithm.They might also choose to use AES if their VPN’s have been recently implemented.
Answers A and B. 3DES is a product of the U.S. that may not be considered trustworthy
enough for domestic German defense work, because it was entirely foreign developed. El
Gamal is not a symmetric algorithm, and typically only symmetric algorithms are used for ses-
sion encryption in a VPN setup.

4. The primary limitation of symmetric cryptography is:
A. Key size
B. Processing power
C. Key distribution
D. Brute-force attacks

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