A function that takes a variable-length string and creates a fixed-length value is called a:

A.
Key

B.
Digital signature

C.
One-way hash

D.
Encryption

Explanation:
One-way hashing creates a fingerprint of the message so it can more
easily identify and monitor the message to see if it has been altered. It takes a
variable-length string (the message) and generates a fixed-length value (message
digest).