Verify the signature over a string, given the public key
    and base64-encode signature.
    Return True on success.
    Return False on error.

def verify_raw_data(raw_data, pubkey_hex, sigb64):
    """
    Verify the signature over a string, given the public key
    and base64-encode signature.
    Return True on success.
    Return False on error.
    """
    if not isinstance(raw_data, (str, unicode)):
        raise ValueError("data is not a string")

    raw_data = str(raw_data)

    vi = ECVerifier(pubkey_hex, sigb64)
    vi.update(raw_data)
    return vi.verify()