Historical clue formulations

• Writes in C or R, say — 2024-12-12
• Does programming work — 2024-12-05
• Works on a loop, say — 2024-09-21
• Message concealers — 2023-07-10
• Does some tech work — 2023-02-09
• Things that can be cracked — 2020-09-05
• Does some computer work — 2018-09-28
• Does a tech job — 2016-12-13
• Writes in C++, say — 2015-11-08
• Secret writings — 2013-05-14
• Does some computer programming — 2012-09-11
• "One if by land, two if by sea" and others — 2011-06-19
• Buildings often have them — 2008-08-23
• Secret languages — 2007-05-14
• See 5-Across — 2006-02-08
• They may be cracked — 2004-07-22
• Computer programmers' expertise — 2002-11-10
• Crackers may be used on them — 2002-05-17
• Things to crack — 2001-09-12
• Systems of rules — 2001-08-26
• Some are made of bars — 1999-07-09
• Things to crack — 1997-11-25
• Spy secrets — 1996-01-09