BLUF

A minimum of 12 characters should be used, with longer passwords being better.

Summary

KEY POINTS:
  1. A GPU could crack all possible 8-character combinations in under an hour.
  2. Passphrases with four or more random words are the most secure.
  3. Password length is more important than complexity.
  4. Passwords should be truly random, with strength measured by entropy.

References