The most secret Japanese diplomatic cipher, "Purple," was cracked in 1940.

We will have a secret cipher between us, as I had with Harry.

"You had a secret cipher with my Da?"

Instead of writing in plain English, Mary used her own personal secret cipher.

She also thought that if anyone found the messages, then they would not be able to read her secret cipher, but she was wrong again.

She knew enough to use a secret cipher, but not enough to understand that it could be broken.

Is there a secret cipher or are they code words?

Poe also used a secret cipher in his short story 'The Gold Bug'.

Nothing was more luminous than a secret cipher; everything was the hieroglyph of something else.

Aivas had had to delve deeply to find the secret ciphers in the captain's private files.