The WordPress core is…well, the core of WordPress. WordPress core files should almost never be modified, so you’ll want to ensure the md5 checksums of your files match up against the checksums of the original core files provided by WordPress.org. The wp-md5 WordPress core checksum database can be used to compare good, known md5 checksums to the checksums of the WordPress core files on your server. The md5sum of every version of WordPress published to on WordPress.org is available here, and can be accessed in an automated manner by using the following url scheme:
https://wpmd5.mattjung.net/core/version/
So for example, to get the md5sums of the core files for WordPress 5.3.2, you would access them at the following location:
https://wpmd5.mattjung.net/core/5.3.2/
You can also browse all core files and version checkums here.