def check_sequence_signing_type(sequence):
    """
    Checks that only one of signing_key or self_signed is present in the entry
    """
    for entity in sequence:
        # Check only if the entity has a defined certificate
        if 'certificate' not in entity:
            continue
        cert = entity['certificate']

        # Check the keys are not present at the same time
        if 'signing_key' in cert and 'self_signed' in cert:
            return {
                'result': False,
                'message': ("The certificate '%s' can't define signing_key and self_signed at the "
                            "same time.") % entity['name']
            }

    return {
        'result': True,
        'message': "All certificates have a correct private key attribute."
    }