So I make a research on my own. I have a device it allows a 64bit message. I wanted to secure it but I 64bits arent just enough to hash it and encrypt it. Is there really any good Hash function out there that can produce a 64bit result from a seed of 128bit ? I tried to search but there are many limitations. Note I use micro controller so a lightweight one is a must "key"

  • $\begingroup$ Conceptually, it is always possible to write a hash function from any number of bits to any other number of bits, no problem. For example, you could just truncate the hash function that gives too many bits. I guess you are asking about specific hash functions available in C though? For that it would likely be better to ask this on a different site. $\endgroup$
    – 6005
    Mar 31 '20 at 13:34
  • $\begingroup$ What is your end goal? What do you want to do with those 64 bits? $\endgroup$
    – ComFreek
    Mar 31 '20 at 17:03
  • $\begingroup$ As I mentioned @ComFreek the controller that im using accepts only 64bits of message. I can explain more in private $\endgroup$ Mar 31 '20 at 18:10
  • $\begingroup$ Sorry; we're not looking for private questions. We're a public resource, so we require your question to state all relevant information needed to understand the question and to evaluate possible answers. What properties do you need the hash function to have? Without knowing that, it seems unlikely that the question will be a good fit here. You mention something about security; how does that relate to your question about seeking a hash function? $\endgroup$
    – D.W.
    Mar 31 '20 at 20:57
  • $\begingroup$ As I stated I want the function to get a 128bit input and produce an 64bit (cause the real message could be up too 64bit and I want to add the hash of it with the realmessage). Also there is the need of security because if the micro controller gets compromised then whoever stole the messages cannot get the real message. $\endgroup$ Mar 31 '20 at 21:09

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