# safe concating PRP and PRG

Suppose it is necessary to build a safe PRG. You have one PRP with $$\epsilon = \frac{1}{2} ^ {45}$$, and one PRF with $$\epsilon = \frac{1}{2} ^ {55}$$. There is no mathematical relationship in the PRP to PRF.

• Can a safe PRG be built with them?

• Does anyone have an explanation for this?

• Because as far as i know when you have a repetition of $$\epsilon = \frac{1}{2} ^ {80}$$ then it is considered as the standard of a good encryption unless it is below but is there any trick here about this question?

• Welcome to Cryptography. We have $LaTeX/MathJax$ enabled in our site. Check the editions. Does this homework? – kelalaka Feb 13 '20 at 13:49