A cryptographic algorithm is also known as:

A.
A key

B.
Cryptanalysis

C.
A cipher

D.
A cryptosystem

Explanation:
Acipher is a cryptographic transformation that operates on characters
or bits. In different words, a cipher is defined as a cryptographic
algorithm or mathematical function that operates on characters or
bits and implements encryption or decryption. In contrast, a code
operates with words, phrases and sentences. In a code, a word may
be the encipherment of a sentence or phrase. For example, the word
SCARF may be the code for the term BEWARE OF DUTCH TRAITOR
IN YOUR MIDST.
* a cryptosystem is a set of transformations from a message
space to a ciphertext space. This system includes all cryptovariables
(keys), plaintexts and ciphertexts associated with the
transformation algorithm. The difference between answers a and c is
that answer c, the correct answer, refers to the algorithm alone and
answer a refers to the algorithm and all plaintexts, ciphertexts and
cryptovariables associated with this algorithm.
* cryptanalysis, refers to being able to break the cipher
so that the encrypted message can be read. Cryptanalysis may be
accomplished by exploiting weaknesses in the cipher or, in some
fashion, determining the key. This act of obtaining the plaintext or
key from the ciphertext can be used to recover sensitive or classified
information and, perhaps, to pass on altered or fake messages in
order to deceive the original intended recipient.
* the key or cryptovariable, is used with a particular algorithm
to encipher or decipher the plaintext message. By using the
key, the algorithm can be publicly known and evaluated for its
strength against attack. The key associated with a particular transformation
or algorithm can take on many values and the range of all of
these possible values is called the keyspace. Ideally, an enciphered
plaintext message using a specific algorithm will produce a unique
ciphertext message for each different key that is used with that algorithm.
The situation in which a plaintext message generates identical

ciphertext messages using the same transformation algorithm, but
with different cryptovariables, is called key clustering. Obviously, this
is not a desirable situation, since it effectively reduces the number of
keys that have to be tried by an attacker in order to recover the plaintext.