While online service providers are sometimes accused of forwarding identifying customer information as name and address to untrusted third parties, comparatively little attention is paid to the input data that customers provide explicitly to the service. If the input data is sensitive but the service provider is not completely trustworthy, this constitutes a serious privacy problem. From a privacy-defending point of view, the most desirable situation would be for the service not to require any kind of sensitive information at any time, while still yielding useful results for the customer. This paper presents a service architecture that allows for the use of a restricted number of services without requiring the transmission of unencrypted customer data to the service provider. The supported services include the execution of basic database and arithmetic operations that can be combined in numerous useful ways. The basic idea of this architecture is to transform sensitive data on the client side before transferring it to the service provider. The latter processes the transformed data without being able to draw any further conclusions from it. The pseudo-result obtained is returned to the customer who applies a special retransformation to obtain the actual result.