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CONT: Keying elements. - In preparing the device for encipherment or decipherment, the operator uses two keying elements: a daily keying element and a message keying element. ... Message keying element. - The ""channel elimination"" or ""interruptor"" scheme of encipherment is used with strip cipher systems. In order to maintain a high degree of security, both the particular channels eliminated and the total number of channels eliminated should vary among messages enciphered on the same day. The internal message indicator is the message keying element and determines the number and identity of channels eliminated in enciphering or deciphering a particular message.