def is_ebx(line):
    """Determines whether the line of code is a part of the rolling
    key update (EBX register).

    Args:
        line (AsmBlock): one asm instruction with its operands
    """
    return (len(line.args) >= 1
            and str(line.args[0]) in ["EBX", "BX", "BL"]
            and not line.name == "MOV")