These are the files:
data\global\sfx\cursor\curindx.wav - User Name (d2sfx.mpq)
data\global\sfx\cursor\wavindx.wav - Regular key (d2sfx.mpq)
data\global\chars\am\cof\amblxbow.cof - Expansion key (d2char.mpq)

They are encrypted.

You won't be able to find these in your registry