They were only used for the most important and secret communications.

There was a secret communication to him in it, though.

It seemed to him that he had intercepted some secret communication between them.

It is possible they believe an absolutely secure secret communications system would give them an advantage over the Chinese.

Many of these hill state rulers entered into the secret communication with the British.

Never before had a nation entrusted so much of its secret communications to a single device.

The word cryptography became the more familiar term for secret communications from the middle of the 17th century.

A time-consuming technique, usually reserved for only the most secret communications.

But I had seen him do nothing that indicated him to be in secret communication with anybody.

Such was the way with secret communications between The Shadow and his agents.