How to encrypt and decrypt a transposition cipher?

Question

I encrypted the text hello there with a 3x4 table with the key 2 1 3. I fill in the text into the table row by row and got the ciphertext eohehltrl_ex(reading by column). So if I were to decrypt this ciphertext into the plaintext what should I do? I made a 3x4 table again and filled it in row by row (according to online tutorials). However, I couldn't get the same text anymore. Do I fill in the ciphertext into the table by columns? I did my homework on decrypting a transpostion cipher(I fill in the ciphertext into the table by rows and I got the answer); however when I tried encrypting and decrypting my own text I couldn't do it.

Does anyone know what I am doing wrong?

Answer 1

For Decryption Process, use the reverse of encryption process. I think you are using a wrong table format. The table should be 4*3 instead of 3*4. Now, Write your encrypted text column by column(4 rows and 3 cols). It will be like this.

e h l

o l _

h t e

e r x

Now, Apply the decryption key of key 2 1 3. The decryption key will be the same.

2 1 3

| | |

2 1 3

Now, arrange the message in columns from above by making necessary transformations. The table will become,

h e l

l o _

t h e

r e x

Now, Read row by row. Your Message will be

hello there

Remember, For decryption, apply the same process for encryption in reverse order. Hope that helps. :)