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Double Transposition



First, choose a key. A grid is created below the key and the message to be encoded is written from left to right. Numbers are written above the grid. The numbers are random. Then the grid is read vertically and arranged in the order of the numbers. The letter "Z" is used to fill in blank spaces found in the grid.

The message "this is a simple cipher" after being encoded with double transposition. The key for the following example is "ENCODING".

E

N

C

O

D

I

N

G

8

2

3

5

4

7

1

6

T

H

I

S

I

S

A

S

I

M

P

L

E

C

I

P

H

E

R

Z

Z

Z

Z

Z

The message would read: AIZHMEIPRIEZSLZSPZSCZTIH

After this, repeat the method with another key(DECODING).

Note: The key does not have to be of the same length.

D

E

C

O

D

I

N

G

7

2

1

6

8

3

5

4

A

I

Z

H

M

E

I

P

R

I

E

Z

S

L

Z

S

P

Z

S

C

Z

T

I

H

And finally: ZESIIZELTPSHIZIHZCARPMSZ

To decipher this cipher, reverse the process.