Possible Clues:

• Make cryptic in French - Napoleonic, perhaps
• Make it hard to read the enclosed poem
• Need to be about to make the top of 24 down hard to understand
• Secure, in a way
• Put into secret symbols
• Make unreadable, for security
• Put into secret writing
• Convert to dots and dashes
• Make hard to figure out
• Do some espionage work