Passwords

Don’ts

  • Don’t limit what characters users can enter for passwords. Only idiots do this.
  • Don’t limit the length of a password. If your users want a sentence with supercalifragilisticexpialidocious in it, don’t prevent them from using it.
  • Never store your user’s password in plain-text.
  • Never email a password to your user except when they have lost theirs, and you sent a temporary one.
  • Never, ever log passwords in any manner.
  • Never hash passwords with SHA1 or MD5 or even SHA256! Modern crackers can exceed 60 and 180 billion hashes/second (respectively).
  • Don’t mix bcrypt and with the raw output of hash(), either use hex output or base64_encode it. (This applies to any input that may have a rogue \0 in it, which can seriously weaken security.)

Dos

  • Use scrypt when you can; bcrypt if you cannot.
  • Use PBKDF2 if you cannot use either bcrypt or scrypt, with SHA2 hashes.
  • Reset everyone’s passwords when the database is compromised.
  • Implement a reasonable 8-10 character minimum length, plus require at least 1 upper case letter, 1 lower case letter, a number, and a symbol. This will improve the entropy of the password, in turn making it harder to crack. (See the “What makes a good password?” section for some debate.)

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