Confidentiality and Integrity: A Constructive Perspective

Traditional security definitions in the context of secure communication specify properties of cryptographic schemes. For symmetric encryption schemes, these properties are intended to capture the protection of the confidentiality or the integrity of the encrypted messages. A vast variety of such definitions has emerged in the literature and, despite the efforts of previous work, the relations and interplay of many of these notions (which are a priori not composable) are unexplored. Also, the exact guarantees implied by the properties are hard to understand. In constructive cryptography, notions such as confidentiality and integrity appear as attributes of channels, i.e., the communication itself. This makes the guarantees achieved by cryptographic schemes explicit, and leads to security definitions that are composable. In this work, we follow the approach of constructive cryptography, questioning the justification for the existing (game-based) security definitions. In particular, we compare these definitions with related constructive notions and find that some are too weak, such as INT-PTXT, or artificially strong, such as INT-CTXT. Others appear unsuitable for symmetric encryption, such as IND-CCA.