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Which of the following is NOT a symmetric key algorithm?

Which of the following is NOT a symmetric key algorithm?

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A.
Blowfish

B.
Digital Signature Standard (DSS)

C.
Triple DES (3DES)

D.
RC5

Explanation:
Digital Signature Standard (DSS) is not a symmetric key algorithm; it is an asymmetric key algorithm.
Because digital signatures are so important in proving who sent which messages, the U.S. government decided
to establish standards pertaining to their functions and acceptable use. In 1991, NIST proposed a federal
standard called the Digital Signature Standard (DSS). It was developed for federal departments and agencies,
but most vendors also designed their products to meet these specifications. The federal government requires
its departments to use DSA, RSA, or the elliptic curve digital signature algorithm (ECDSA) and SHA. SHA
creates a 160-bit message digest output, which is then inputted into one of the three mentioned digital signature
algorithms. SHA is used to ensure the integrity of the message, and the other algorithms are used to digitally
sign the message. This is an example of how two different algorithms are combined to provide the right
combination of security services. RSA and DSA are the best known and most widely used digital signature
algorithms. DSA was developed by the NSA. Unlike RSA, DSA can be used only for digital signatures, and DSA
is slower than RSA in signature verification. RSA can be used for digital signatures, encryption, and secure
distribution of symmetric keys.
Incorrect Answers:
A: Blowfish is a block symmetric cipher that uses 64-bit block sizes and variable-length keys.
C: Triple DES is a symmetric cipher that applies DES three times to each block of data during the encryption
process.
D: RC5 is a block symmetric cipher that uses variable block sizes (32, 64, 128) and variable-length key sizes
(0–2040).

Harris, Shon, All In One CISSP Exam Guide, 6th Edition, McGraw-Hill, 2013, p. 832


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