4.4 Computational security
Compared to information-theoretical security, the concept of computational security is weaker in the sense that such cryptographic schemes can, in principle, be broken if Eve has enough time and sufficient computational resources.
However, the amount of computations needed to break a computationally secure scheme is so large that a break is absolutely infeasible in practice. As an example, if a scheme cannot be broken with a probability higher than 10−40 in 300 years using the fastest supercomputer available today (or in the near future), then that cryptographic scheme is sufficiently secure for all practical purposes.
On the positive side, computational security bypasses the limitations of perfect secrecy. As discussed in [97], perfect information-theoretical security suffers from the required key length: the secret key that Alice and Bob need to exchange before they can start communicating securely must have the same length as the overall length...
