title: Minimum key length of RSA
body: <p>When I implemented a license key mechanism in C# using RSA, I came across the <a href="http://msdn.microsoft.com/en-us/library/system.security.cryptography.rsacryptoserviceprovider.aspx" rel="nofollow">RSACryptoServiceProvider class</a>, which is limited to a minimum of 384 bit key size. This key length has direct impact on the signature (==license key) which I created.</p>
  
  <p><strong>Is 384 bits a technical limit of RSA in general or might it be possible to implement RSA successfully with even shorter key sizes?</strong></p>
  
  <p>Reading the (German) Wikipedia article which explains RSA, they use very small prime numbers in their mathematics calculation example. That seems to work, so I would expect the key size to be shorter than 20 bits... Note: I absolutely don't care about security at the moment. That's another discussion. I'll just want to get the technical limits right.</p>
  
  <p><em>I know Stackoverflow should not be used to ask for tools, but if you know a .NET RSA library which has a lower limit, maybe you just want to mention that as a side note.</em></p>