For a quick reference of the Dex file format, Ange Albertini (known for PoC||GTFO) made a poster: https://github.com/corkami/pics/blob/master/binary/DalvikEXe...

All his posters are pretty amazing: https://github.com/corkami/pics/blob/master/binary/README.md

> The next value is a checksum, which is calculated by applying a function to the contents of the entire file, excluding any bytes preceding the checksum.

[...]

> The header also includes a SHA-1 hash of the file (excluding any preceding bytes).

Wait, each checksum includes the other? How does that work?