Historical clue formulations

• Made some Java, say — 2025-09-26
• Like some hard-to-read messages — 2022-12-17
• Needing a key, perhaps — 2020-06-12
• In need of a cracker, perhaps — 2015-10-04
• In secret language — 2007-04-23
• Requiring cracking, perhaps — 2005-01-07
• Like something written in 21-Across — 2001-10-07
• Like DNA — 2001-09-09
• Having secret marks, maybe — 2001-06-26
• Like many wartime messages — 1999-12-19
• Unreadable — 1998-07-04