Generate Random numbers without using any external functions

Question

This was questions asked in one of the interviews that I recently attended.

As far as I know a random number between two numbers can be generated as follows

Answer 1

Here I am suggesting some sources with comment may be you find helpful:

• System Time : Monotonic in a day poor random. Fast, Easy.
• Mouse Point : Random But not useful on standalone system.
• Raw Socket/ Local Network (Packet 's info-part ) : Good Random Technical and time consuming - Possible to model a attack mode to reduce randomness.
• Some input text with permutation : Fast, Common way and good too (in my opinion).
• Timing of the Interrupt due to keyboard, disk-drive and other events: Common way – error prone if not used carefully.
• Another approach is to feed an analog noise signal : example like temp.

• /proc file data: On Linux system. I feel you should use this.

  /proc/sys/kernel/random: This directory contains various parameters controlling the operation of the file /dev/random.

  The character special files /dev/random and /dev/urandom (present since Linux 1.3.30) provide an interface to the kernel's random number generator.

  try this commads:

  $cat /dev/urandom   
  

  and

  $cat /dev/random
  

  You can write a file read function that read from this file.

  Read (also suggests): Is a rand from /dev/urandom secure for a login key?

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