To allow a small C++ application to update itself at clients connected over the internet, I am in need of a mechanism that validates the download based on a public key. Algorithms such as DSA or RSA seem to be able to do this nicely.
However, looking at well-known available libraries for this (Crypto++, LibTomCrypt) they all end up making my binary > 500k larger, while it seems to me such logic can be implemented in a couple of k. Are there any libraries that implement RSA/DSA hash verification in a, say, <20k footprint?