But during World War II they used them for messages.

Substitution ciphers are not safe enough to use for important messages.

Thus, any single key must only be used for messages of a fixed and known length.

It was aimed at the solar system, for the drive could be used for messages at this distance.

We learned to make simple ciphers that could be used for messages between brigades and battalions.

The number of colors was increased, and katakana is also used for in-game messages.

Campaign buttons bear some similarity to bumper stickers, which are also used for political and other promotional messages.

Many of the regiments used their own languages or codes for internal messages.

It was the special ink that The Shadow used for important messages.

Most of these involve ogham being used for short messages or inscriptions on wood.