Is it possible to implement an electronic digital signature in PHP?

Question

PHP

Hello!
There is a task to allow users to download files signed using EDS from the site. Without the use of third-party cryptographic packages a la Rutoken, but only by the server. Users are external, not on the local network.
1. Do I understand correctly that a file signed with an EDS is encrypted and cannot be opened/used without a key?
2. Is it possible to sign files only with PHP (or using some server resources through PHP)?
3. If so, how can the user on their side be able to decrypt the file? Is it possible to implement this in JavaScript that will run in the client's browser?
Thank you.

Answer 1

EDS does not encrypt signed documents, it encrypts only their hash.
the answer to questions about the possibility of signing php / zhs depends on how / where the keys are stored.

Answer 2

Pay attention to the myDSS service from CryptoPRO, maybe it will suit you:
https://dss.cryptopro.ru/docs/articles/rest/signse...