Complete the following sentence. A digital signature is a:

A.
hash value that has been encrypted with the sender’s private key

B.
hash value that has been encrypted with the sender’s public key

C.
hash value that has been encrypted with the senders Session key

D.
senders signature signed and scanned in a digital format

Explanation:
A digital signature is a hash value that was encrypted with the sender’s private key.
Digital signatures are based on public key cryptography, also known as asymmetric cryptography. Using a
public key algorithm such as RSA, one can generate two keys that are mathematically linked: one private and
one public. To create a digital signature, signing software (such as an email program) creates a one-way hash
of the electronic data to be signed. The private key is then used to encrypt the hash. The encrypted hash —
along with other information, such as the hashing algorithm — is the digital signature. The reason for encrypting
the hash instead of the entire message or document is that a hash function can convert an arbitrary input into a
fixed length value, which is usually much shorter. This saves time since hashing is much faster than signing.
Incorrect Answers:
B: The hash value is signed with the sender’s private key, not the public key to prove that the message came
from the sender and has not been altered in transit.
C: A session key is not used to encrypt the hash value in a digital signature.
D: A digital signature is not a sender’s signature signed and scanned in a digital format.

Harris, Shon, All In One CISSP Exam Guide, 6th Edition, McGraw-Hill, 2013, p. 829
http://searchsecurity.techtarget.com/definition/digital-signature