> In any case, you don't create a signature on a string per se, you create it on bytes, even if those bytes are derived from a string. Everyone is on the same

> In any case, you don't create a signature on a string per se, you create it on bytes, even if those bytes are derived from a string. Everyone is on the same page that at some point bytes go into a hash function. That's not the problem. You mention JWT, but JWT only does external signing, which doesn't trigger the problematic case several people are describing to you. Perhaps an example would be more useful. If you start with a JSON like: {"a": 1} how do you build a JSON like: {"a": 1, "tag": "deadbeefdeadbeefdeadbeef"} with a signing and verification algorithm that works? > Also, you don't validate a signature by re-creating the bytes in question... that's a flawed approach, and not the approach for example JWT takes. Can you describe an HMAC validation process that doesn't involve recreating the bytes in the HMAC tag?