It looks like Honkai Impact 3rd Stated Encrypting USMs from 7.6 version

[cabera2]

I checked USM files is HI3 and found that USM until ver 7.5 is not Encrypted so you can simply convert with tools like VGMToolBox, but USMs after ver 7.6 can't do the same thing.
I think they also started to encrypting.
Maybe this tool can use on HI3 too now.(only if someone get the keys)