Coreutils sum, 8 6 bytes
The old System VGnu Coreutils sum, (obsolescent but remains available for compatibility) takes an input stream or a file. The -s flag invokes BSD checksumold System V logic, which just adds up the byte values.
Bonus score: 533⭐️
sum -s Try it online! 8 bytes
(similar to Notes:
* sum defaults to the BSD checksum algorithm which is also obsolescent
* Bonus score: 533⭐️
* related q:258739)