16. Outline an automated attack on a double transposition cipher (of the type discussed in the text), assuming that the size of the matrix is known. 17. A double transposition cipher can be made much stronger by using the following approach. First, the plaintext is put into an n x m array, as described in the text. Next, permute the columns, and then write out the intermediate ciphertext column by column. That is, column 1 gives the first n ciphertext letters, column 2 gives the next n, and so on. Then repeat the process, that is, put the intermediate ciphertext into an nx marray, permute the columns, and write out the ciphertext column by column. Use this approach, with a 3 * 4 array, and permuttions (2,3,1,4) and (4,2,1,3) to encrypt the plaintext "attackatdawn