Meaning

noun a sports implement with a long handle and a head like a hammer; used in sports (polo or croquet) to hit a ball

noun a light drumstick with a rounded head that is used to strike such percussion instruments as chimes, kettledrums, marimbas, glockenspiels, etc.

noun a tool resembling a hammer but with a large head (usually wooden); used to drive wedges or ram down paving stones or for crushing or beating or flattening or smoothing

originCryptographic scenarios use archetypal characters with standard names chosen to remember their role: Mallet was derived from "malicious" and "man-in-the-middle attack", as well as the tool mallet.

Etymology from Wiktionary, CC BY-SA 3.0