# Week 10

Hi everyone, Rupam here. This week I completed adding tests which were left in the [PR](https://github.com/prysmaticlabs/prysm/pull/14278) which implements the function to calculate the roots of all fields of a block body. This is a part of the implementation of the `compute_merkle_proof` function from CL specs. With this, the PR got merged and right now I am working on another [PR](https://github.com/prysmaticlabs/prysm/pull/14356) which implements a function to calculate the merkle proof of the execution payload field of a block body.

## Calculating the merkle proof of execution payload

According to what [rkapka](https://github.com/rkapka) said:

`execution_payload` is a field of `BeaconBlockBody`, which itself is a field of `BeaconBlock`

This means that the merkle trie will look something like this:

             L
       J             K
   F      G      H      I
 D   E
A B P C

`P` is the `execution_payload` field, `F` is the root of the block body and `L` is the root of the block.
So in this case the merkle proof will consist of the following nodes: `C --> D --> G --> K`

We already have a function `fieldtrie.ProofFromMerkleLayers` that is able to generate a proof for a simple trie. So it is able to produce a proof of `P` if the trie's root is `F` (the proof will be `C --> D`) and a proof of `F` if the trie's root is `L` (the proof will be `G --> K`).

What we can do is call this function twice to obtain a combined proof
First of all, we need roots of all fields of the block body. That way we can construct a proof of execution_payload with respect to the block body. Note that this proof does not contain the root of the block body, but this is very easy to get - we just need to call `HashTreeRoot` on the body.

We then take the root of the body plus roots of all other fields of the block and construct a proof of the block's root. Lastly, we combine these two proofs into one. Each proof is just a slice of bytes that we combine into one slice.

This PR should ideally implement the changes that Capella and Deneb have brought forward once it gets completed.