user137492: In the source code of Bitcoin Core there are these functions but no explanation of how and where they are used. I need to make a description for all crypto-functions used in Bitcoin Core (https://github.com/bitcoin/bitcoin/tree/master/src/crypto) but it's difficult to find information, so asking you here.

user121614: You can open the git history for each file and see when and why they were added.
chacha20.cpp was added in PR #9792, apparently to improve Bitcoin Core's random number generator. chacha_poly_aead.cpp was added in PR #15649 as a preliminary step for implementing BIP324 (the P2P encrypted transport protocol).

137492: <p>In the source code of Bitcoin Core there are these functions but no explanation of how and where they are used. I need to make a description for all crypto-functions used in Bitcoin Core (<a href="https://github.com/bitcoin/bitcoin/tree/master/src/crypto" rel="nofollow noreferrer">https://github.com/bitcoin/bitcoin/tree/master/src/crypto</a>) but it's difficult to find information, so asking you here.</p>
 121614: <p>You can open the git history for each file and see when and why they were added.</p>
<p>chacha20.cpp was added in <a href="https://github.com/bitcoin/bitcoin/pull/9792" rel="nofollow noreferrer">PR #9792</a>, apparently to improve Bitcoin Core's random number generator. chacha_poly_aead.cpp was added in <a href="https://github.com/bitcoin/bitcoin/pull/15649" rel="nofollow noreferrer">PR #15649</a> as a preliminary step for implementing <a href="https://github.com/bitcoin/bips/pull/1378" rel="nofollow noreferrer">BIP324</a> (the P2P encrypted transport protocol).</p>
