DES...

• is a block cipher : it encrypts data in 64 bit blocks. MSW: Hence, for a long thing, we break it into 64 bit blocks and pad the end
• is a symmetric algorithm : the same algorithm and the same key are used for encryption and decryption (apart from minor differences in the key schedule)
• uses keys which
  • are 56 bits long : (we usually express them as 64 bits, with the LSB of the key bytes being ignorable parity bits)
  • can be any number...
  • ...but a few are weak (poor choices) but easily avoided

-- MattWalsh - 30 Apr 2002