Transposition Cipher
A transposition
cipher encrypts messages as follows.
- For a plaintext (e.g., "ABCDEFGHIJKLMNOPQRSTUVWXYZ"), and a key
value k (e.g., 4), you create a matrix whose height is k, and a suitable width
so that the matrix
can accommodate the whole plaintext.
- Note that it is possible that the plaintext message may contain
spaces.
- Fill the plaintext into the matrix in a row-wise order.
If necessary, you may pad the matrix with some random characters (e.g.,
'A', 'E', 'I', 'O', 'U').
- In this exercise, please always use 'A' for padding, so that it
will be easier for the robot to validate your result.
- The matrix may look like
| A | B | C | D | E | F | G
|
| H | I | J | K | L | M | N
|
| O | P | Q | R | S | T | U
|
| V | W | X | Y | Z | A | A
|
- Read the characters out in a column-wise order, this gets you the
ciphertext "AHOVBIPWCJQXDKRYELSZFMTAGNUA".
Write a program to read a line of plaintext, and a key, and output
the encrypted text.
The program may run as follows:
Please input the message to encrypt -- ABCDEFGHIJKLMNOPQRSTUVWXYZ
Please input the key -- 4
AHOVBIPWCJQXDKRYELSZFMTAGNUA
Decrypting the message is simple. As long as you know the key value,
you can re-construct a matrix with height k, and fill in the ciphertext
by column-wise order. Then read out the message in row-wise order, and
you will obtain the original message.
