The SECOM cipher is a handcipher, used to encrypt messages containing letters, numbers and spaces. It is one of the most secure pencel-and paper ciphers ever. SECOM uses four steps: calculating the key phrase digits, the straddling checkerboard, and two columnar transpositions, of which one disrupted. The combination of fractioning by the checkerboard and the double disrupted transposition makes SECOM a higly secure encryption methode.
We will demostrate the encryption technique by the following example:
Plain text: RV TOMORROW AT 1400PM TO COMPLETE TRANSACTION
