Relations among Notions of Security for Public-Key Encryption Schemes

For public-key encryption methods, we examine the relative strengths of common concepts of security. Under chosen plain text attack and two forms of chosen-ciphertext assault, we address the aims of indistinguishability and non-malleability. We establish either an implication (any scheme fulfilling one idea must also meet the other) or a separation for each of the resultant pairs of definitions (there is a scheme meeting one notion but not the other, assuming the first notion can be met at all). In the random oracle paradigm, plaintext awareness is treated in a similar way. This article also includes a new definition of non-malleability, which we feel is more straightforward than the prior one.