Outsourcing a relational database to the cloud offers several benefits, including scalability, availability, and cost-effectiveness. However, there are concerns about the security and confidentiality of the outsourced data. A general approach here would be to encrypt the data with a standardized encryption algorithm and then store the data only encrypted in the cloud. The problem with this approach, however, is that with encryption, important properties of the data such as sorting, format or comparability, which are essential for the functioning of database queries, are lost. One solution to this problem is the use of encryption algorithms, which also preserve these properties in the encrypted data, thus enabling queries to encrypted data. These algorithms range from simple algorithms like Caesar encryption to secure algorithms like mOPE. The report at hand presents a survey on common encryption techniques used for storing data in relation Cloud database services. It presents the applied methods and identifies their characteristics.

翻译：将关系数据库外包至云端可带来可扩展性、可用性与成本效益等诸多优势，然而外包数据的安全性与机密性问题随之而来。常规方法是对数据进行标准化加密算法处理后，仅将密文存储于云端。但该方案存在关键缺陷：加密操作会破坏数据中对于数据库查询功能至关重要的属性（如排序性、格式保留性及可比性）。解决此问题的方案之一，是采用能够在加密数据中保持这些属性的加密算法，从而实现对密文数据的查询能力。此类算法涵盖从凯撒密码等简单算法到mOPE等安全方案。本报告系统梳理了面向关系型云数据库服务中数据存储的通用加密技术，阐述了各类技术的实现方法并归纳其特性。