Main Index Page

xCreated 22/10/2026. Last updated 22/10/2026

This page is being used to collect information about the history of Letter locks and how to defeat them. Please contact me if you know any of this information is incorrect or if you have any other information that should be added. Thank you.

Letterlocks are additional folds, often depending on cuts, which are used to lock a letterfold together in an attempt to make sure it cannot be read in transit.

There is a separate page about Letterfolds, Notes, Covers and Envelopes

The vast majority of the information on this page was contributed by Edwin Corrie.

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1584

There is mention of how to open letterlockeed letters and reseal them without arousing suspicion in 'Magiae Naturalis' by Giambattista della Porta (1535-1615), the first four books of which were published in Latin in Naples in 1558 and which was gradually expanded to twenty books by 1584.

(From Chapter XI of Book 16 - Of Invisible Writing)

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1636

'Deliciae physico mathematicae oder mathematische und philosophische Erquickstunden' by Daniel Schwenter, which was published in Nürnberg in 1636, contains a description of a method of locking a letter.

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1658

An English translation of 'Magiae Naturalis', under the title of 'Natural Magick', and giving the author's name as John Baptista Porta, which was published in London in 1658 translates the Latin cited above (see entry for 1584) as:

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The method of locking a letter explained in Schwenter 1636 also appears:

1679

In 'Der Curiose Schreiber' by Johannes Christoph Mieth, which was published in Dresden in 1679.

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1703

In 'Der zu vielen Wissebschafften dienstlich-anweisende Curiose Kunstler' by Adam Friedrich Kirsch, which was published by Johan Leonhard Buggel in 1703.

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1759

In 'Onomatologia curiosa artificiosa et magica oder ganz natürliches Zauber-lexicon', which was published in 1759.

Columns 256/7

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1791

In Volume 5 of 'Die natürliche Magie' by Johann Christian Wiegleb which was published by Friedrich Nocolai in Berlin and Stettin in 1791.

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