title: Shortest hash? MD5 / SHA . First chars, git
body: <p>I need hash function. Users will be write these hash to computer so hash should be short.
  I will have about 50 000 000 records in database. Each must have own hash. I would like to have unique hashes. But if a little records have the same hash, I can accept. Unique is better.</p>
  
  <p>MD2 is good secure for me, but hash is long: "8350e5a3e24c153df2275c9f80692773" - 32 chars. If you must write 10 MD2 hash on keybord you do not happy...</p>
  
  <p>Git use SHA1 for each commit (40 chars). But in output show only first 7 chars:</p>
  
  <pre><code>$ git log
  commit e2cfc89fae5b43594b2c649fd4c05bcc6d2d12ac
  ...
  commit 56a8b4c50d4269dc3f88727472933fd81231f63b
  ...
  commit ce2e9ddbe896b9592abbd5fcb6604b181809d523
  ...
  commit 498c49833516ea33b6a40697634ea6e3cfd62328
  ...
  commit b7d78aea415e64d8d441f9747fe6d5d48fe54ee5
  
  $ git log --oneline | head -n 5
  e2cfc89 commnit message...
  56a8b4c commnit message...
  ce2e9dd commnit message...
  498c498 commnit message...
  b7d78ae commnit message...
  </code></pre>
  
  <p>How is it secure/unique? If I will use for example first 5 or 10 chars from MD5/SHA-1/SHA-256 is it enough secure?</p>
  
  <p>Thank you.</p>