[0d0a]

This tool served as a base for a fun project of mine [0], which consisted on injecting arbitrary bytes to a deflate stream without affecting the decompression output.

The main idea is that a stream is composed of blocks, and dynamic blocks can contain Huffman tables followed by a end-of-block symbol. Since there's no other symbols, such blocks won't produce any output when decompressed. So there's a few bytes for those tables that can be changed (e.g. to put a little ascii signature). However, this affects the codes present in the tables, which must pass some validations (for decompressors to unambiguously match parsed bits to codes). I used a SMT solver to figure out values for the remaining bytes, so that the tables had valid code counts.

[0]: https://nevesnunes.github.io/blog/2021/09/29/Decompression-M...