e  not in ``symbols``.

    Examples
    ========

    >>> from sympy.crypto.crypto import padded_key
    >>> padded_key('PUPPY', 'OPQRSTUVWXY')
    'PUYOQRSTVWX'
    >>> padded_key('RSA', 'ARTIST')
    Traceback (most recent call last):
    ...
    ValueError: duplicate characters in symbols: T

    rC