# Question on SRS of plonk

**URL:** <https://www.plonk.cafe/t/question-on-srs-of-plonk/84>\
**Category:** Research\
**Created:** [20 July 2020 06:00 UTC](https://www.plonk.cafe/t/question-on-srs-of-plonk/84 "2020-07-20T06:00:44Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![shenmue](https://dub1.discourse-cdn.com/flex017/user_avatar/www.plonk.cafe/shenmue/32/42_2.png) [@shenmue](https://www.plonk.cafe/u/shenmue)\
**Post date:** [20 July 2020 06:00 UTC](https://www.plonk.cafe/t/question-on-srs-of-plonk/84/1 "2020-07-20T06:00:44Z")

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I am new to this field. I have a noob question regarding the srs of plonk.

In page 4, table 1, this work (fast prover): the size of SRS is given by d G1, 1G2 (column 2). the size of CRS/SRS (column 3) is n+a G1, 1G2, where n is number of multiplication gate and a is number of addition gate. The total number of gate is n+a.

Here are my understanding:

1. (column 2) Since SRS consists of monomials (universal), in this case, its [x]\_1, …, [x^d]\_1, we can use SRS to construct kate commitment for polynomial of degree \<= d. Adversary A can update the SRS anytime if she wants to.

2. (column 3) CRS/SRS here are specialized circuit for a specific program, the PLONK circuit. Thus, the lagrange polynomial degree is at most n+a. i.e. deg(L\_i) \<= n+a. Also, the permutation polynomial Z(x) has degree n+a.

3. Now I am confused. My understanding is that we have to construct the CRS gate using the monomials from SRS (column 2). But the degree of SRS is at most d. And n + a is program specific. Does that mean we have to pick a d large enough so that d \>= n+a?

If I am wrong at any where, please correct me. Thanks!

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**Author:** ![arielgabizon](https://dub1.discourse-cdn.com/flex017/user_avatar/www.plonk.cafe/arielgabizon/32/10_2.png) [@arielgabizon](https://www.plonk.cafe/u/arielgabizon)\
**Post date:** [20 July 2020 12:10 UTC](https://www.plonk.cafe/t/question-on-srs-of-plonk/84/2 "2020-07-20T12:10:46Z")

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Hi,  
Yes exactly you must pick d as an upper bound on n+a for all circuits you will use when doing the ceremony; you cannot increase it while updating SRS.