Section: Asset Security

Explanation/Reference:
Explanation:
A cryptographic hash function is a hash function which is considered practically impossible to invert, that is, to recreate the input data from its hash value alone.
The input data is often called the message, and the hash value is often called the message digest or simply the digest.
Incorrect Answers:
A: To create a digital signature, a message digest is calculated (by the hash algorithm being applied to the message) then it is encrypted with the sender's private key. However, the digital signature is not the direct output of the hash algorithm being applied to the message.
B: A ciphertext is the output of an encryption algorithm, not a hash algorithm being applied to data.
D: A plaintext is the message 'before' the hash algorithm is applied to the message; it is the input to the hash algorithm, not the output.
References:
https://en.wikipedia.org/wiki/Cryptographic_hash_function
Krutz, Ronald L. and Russel Dean Vines, The CISSP Prep Guide: Mastering the Ten Domains of Computer Security, John Wiley & Sons, New York, 2001, p. 151

Only servers providing public access to required services should be located in the DMZ.
"Web server" is incorrect. An organization's public web site is a very common DMZ scenario.
"External DNS server" is incorrect. An organization's external DNS servers is a very common DMZ scenario.
"Mail relay" is incorrect. An organization's mail relay is a very common DMZ scenario.
References:
CBK, p. 434
AIO3, p. 483

The correct answer is removing redundant data.