Is it possible with php or js to read SIG file data?

Question

PHP

Actually, the question is in the title.

Answer 1

Usually, the first line of this sig file (if it is in base64 text format, and not binary, of course) contains information about the encryption algorithm. Find a library for working with this algorithm (at least for js, at least for php) and, if you have a public key, decode this signature without any problems.
I used the libraries openpgp.js and TweetNaCl.js, played a little bit with jsencrypt for the RSA algorithm, no problems, the signature is decoded. For php, too, of course, there are libraries for different algorithms. The main thing is to know the encoding algorithm and have a public key.