srm and shred are both filesystem and hardware dependent, and are likely not to actually overwrite the original bits on disk for many common setups these days. Never write anything raw to disk that could complicate your life if it were disclosed to the entire world somehow.

Does shred work with SSD drives?

Does srm? My understanding is that you can't really do this with SSD drives because even writing to the same file, the underlying location of the data may change due to the internal wear-leveling mechanisms. There is no way to guarantee that you are overwriting the same physical 'block' of data on the hardware.