Related Clues:

• See 5-Across
• Things to crack
• Rules
• Some are made of bars
• See 9-Down
• Ciphers
• See 71-Across
• Systems of rules
• They may be cracked
• Writes software
• They're sometimes cracked
• Crackers may be used on them
• Computer programmers' expertise
• Secret stuff
• Cryptographer's study