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  • The answers you already have are very good and explain what you asked. TLDR: The Random Number Generator creates pseudo-random numbers using a known algorithm, so, if someone get a series of random numbers generated by your machine, they can guess the next number and you're in danger that some stranger will hack whatever you are doing with the random numbers. When you add entropy, there is some unexpectedness in the generation of random numbers. If your Pi is used only internally, there is no harm in avoiding the entropy and gaining some CPU power back. Commented Jun 19 at 19:18
  • Thanks @fernando.reyes, I gathered that from the cryptography Q&A I linked. My question is: do I need rngd to achieve that? Commented Jun 19 at 19:57
  • Without rngd you will just have pseudo-random numbers, that I believe are good enough in your case, and you really don't need rngd. Commented Jun 19 at 19:58
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    without RNGD you have pseudo-random numbers plus kernel collected entropy. Is that enough? Idunno, what is the value you get from /proc/sys/kernel/random/entropy_avail ? And is that number high enough ( or at least, not zero frequently enough) to satisfy your need for security. Commented Jun 20 at 4:02
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    entropy_avail is mostly meaningless in recent kernels. Some userspace programs check it so I guess it's kept around for that reason. I still save/load random seeds, and tickle the random device early using haveged, as it was still possible until recently to encounter corner cases (like this example) when using urandom too early. Commented Jun 20 at 9:01