# #StackBounty: #diffie-hellman #discrete-logarithm How to choose the appropriate Smoothness Bound while using the Index Calculus method

### Bounty: 50

While implementing the Quadratic Sieve, the textbooks give a rough formula for what Smoothness bound you should use in your Factor Base.

To factor a number N using the Quadratic Sieve, we can use the following:

$$L = e^{sqrt {ln(N)ln(ln(N))}}$$, $$B = L^{frac {1}{sqrt 2}}$$

For the Index Calculus method for solving the Discrete Log problem in $$mathbb F_p$$, is there a similar formula? Many of the texts I checked, just say choose an appropriate Smoothness Bound B. But don’t give any indication of how one chooses an appropriate B.

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