The Central Intelligence Agency didn’t exist in the first world war, but the US government was even then offering official advice to its secret agents.

9 Secret Letters to Write For "Reflection, Growth, and Transformation" By Nicole Yi Updated on Aug 1, 2017 at 10:05 AM Unsplash | Freddy Castro ...

These included writing hidden messages using every fifth word, substituting letters in what's known as a substitution cipher, or using a telephone number cipher so that letters indicated phone ...

Invisible ink is one of the most popular methods to send secret messages, created with recipes using substances like milk, lemon juice, or urine.

Be it snail mail, a text message, a work email or a birthday card to grandma: good personal writing can foster authentic connection, boost your creativity and brighten someone's day. But personal ...

Discover how FontCode technology hides secret messages in text, making messages machine-readable yet invisible to the human eye.

You could write unbreakable secret messages using chemicals in your fridge or medicine cabinet.

Whether it’s hiding messages under the stamps on letters or writing in invisible ink, people have always found ingenious ways of using whatever technology they have available to write secret ...

From letters to apps, the secret code language of lovers How generations of Valentines have invented ways of writing for one reader alone ...