I am currently studying the most widely known encryption algorithms and methodologies. For practice purposes, I want to implement everything from ECB to RSA as some kind of a C crypto library.
How would I generate a secure key in a C program (I know, that writing a crypto library on my own is not secure at all but I just want to learn basic principles from key generating to key exchanging to encryption mechanisms).
How could I approach the problem of implementing an algorithm for a secure key generation? Which main issues need to be considered to reach an at least mediocre key security?