INT 21 U - DR-DOS 5.0-6.0 internal - GET ENCRYPTED PASSWORD
        AX = 4304h
        DS:DX -> ASCIZ filename
        ???
Return: CF clear if successful
            CX = AX = 0000h if no password assigned to file
        CF set on error
            AX = error code (see AH=59h)
Note:   this function is only supported by DR-DOS 5.0 and 6.0 and DRMDOS 5.1
SeeAlso: AX=4303h,AX=4305h

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