Muller, a spy who masqueraded as a Russian shipbroker and covertly traveled to England among a crowd of refugees in 1915, used pen nibs dipped in lemon to write invisible messages to his counterparts.

A Hillhouse student’s eyes widened as he applied grape juice and heat to what appeared to be a blank piece of paper — but instead held a secret message in invisible ink, written as part of a course ...

Scientists say that hiding secret messages using AI chatbots could lead to a world of iron-clad encryption.

Scientists responded to this challenge by developing an encryption method hidden in AI-generated conversations, making secret messages invisible to cybersecurity and surveillance systems.