Nanotechnology

Key (lock)

Inkwell

Philosophy

Encryption

Materials science

Covert

Computer science

Linguistics

Speech recognition

Computer security

Chemistry - A European Journal

Security inks based on photoluminescent materials are mostly investigated for security applications, such as information encryption and decryption, anti‐counterfeiting, and data storage. Although they are invisible to the naked eye under ambient light, they can be detected under ultraviolet or near‐infrared light. Herein, a new kind of secret paper made from network‐structured ultralong hydroxyapatite nanowires and cellulose fibers has been developed. White vinegar, a common cooking ingredient, is used as an invisible security ink. Covert information on the secret paper written with white vinegar is totally invisible under natural light, but it can be decrypted and clearly read after exposure to fire; the response time to fire is short (&lt;10 s). The ways of writing on the secret paper are diverse by using various pens loaded with white vinegar.

Secret Paper with Vinegar as an Invisible Security Ink and Fire as a Decryption Key for Information Protection