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Prehistoric evidence indicates that people have always been
concerned with detecting whether others have tampered with their
belongings. Early human beings may have swept the ground in front of
their dwellings to detect trespassers' footprints. At least 7,000
years ago, intricate stone carvings were pressed into clay to seal
jars and later, writing tablets. What is the most secure way to
ensure that people are not messing with your things? Roger
Johnston's tests have covered everything from ancient clay seals to
metal flange seals used to secure cargo containers and electronic
seals used on nuclear material. He has found that high-tech,
expensive seals are often no more reliable, and factors such as
properly training inspectors to know what to look for are often just
as important as the seal itself. Johnston has also developed some
new electronic seals that are harder to defeat because they use
"anti-evidence": They provide the correct passcode only
when they are not tampered with, and the passcode is erased if they
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