I am sad that at no point in the text was it ever explained how letter locks protect the letters!
A rather unfortunate admission from an otherwise great article.
A rather unfortunate admission from an otherwise great article.
The standard letter lock was a wax seal: that is a blob of sealing wax with an impression of a stamp or signet ring. A signet ring had an intricate design that was difficult to forge.
A standard wax seal could be defeated by sliding a thin heated knife between the seal and the paper. This melted a little of the wax at the base of the seal, enough to separate it from the paper. Then the letter could be read and the wax seal reattached using the same heated knife.
The purpose of the complex letter locks described in the article was to make the hot knife technique more difficult, by embedding the end of a cut-out strip of paper into the seal so that when the eavesdropper slid their hot knife underneath the seal it would cut the strip.
On the other hand, it may very well be that some types of letter locks were designed such that the letter may be ripped apart if it is opened the wrong way...
Some explosive or easily burning material beneath the seal could thwart attempts at using heat to remove the seal without breaking it. You could also use the technology of a match box to put the letter on fire if opened in the wrong way, or use small glass containers that wrap around folds like paper clips do, and, when broken, release a chemical that destroys the letter (killing the culprit trying to read it without knowing how to open the letter also would be an option). Another option is a device that cannot be opened in an oxygen-rich atmosphere.
The challenge, of course, would be to seal such a letter, and to safely transport it (big seals already can be a challenge there, as they can easily break)
yes