Lecture 3 : One - Way Encryption , RSA Example

We look at a different security property one might require of encryption, namely one-way security. The notion is natural and seems like a minimal requirement on an encryption scheme. It makes sense for both symmetric and public-key encryption schemes. To make the discussion more concrete, we look at the so-called “textbook” variant of the RSA encryption, and see how to pick keys in relation to the security parameter so that the best algorithms that invert RSA are either inefficient or have only negligible advantage. We will also see that while the “textbook RSA” can plausibly be oneway secure, it is definitely not secure in the sense of indistinguishabibility (this security property of encryption schemes was defined in the last class). This shows us that one-wayness is a weaker notion than indistinguishability.