Why are DES keys considered weak keys?

Why are DES keys considered weak keys?

• They are more resource intensive.
• DES weak keys are difficult to manage.
• They produce identical subkeys.
• DES weak keys use very long key sizes.
  

  Answers Explanation & Hints: Weak keys, whether part of an existing encryption algorithm or manually generated, reveal regularities in encryption. This creates a shortcut by which a hacker can break the encryption. DES has four keys for which encryption is identical to decryption.