Step 1: Formation of Secret Key

• For this purpose, the keyword given is “domestic”.
• Therefore the secret key is:

1. Intiially start filling in the keyword from extreme left.

2. We by default consider I/J to be together unless specified otherwise.

3. Now once all letters of keywords are assigned, we start from A and start writing all those alphabets which are not present in keyword.

Step 2: Create cipher text

1. If same alphabet if repeated in plain-text e.g. “d in hidden”, then we split them with a $“\underline{x}”$ in between i.e. “dx” and “de”

2. Now spot the two letters in the 5x5 matrix. If

• They both are in same ROW: $\rightarrow$ then ciphertext is the alphabet to the next-right of it. E.g. for “de” , cipher-text is “os”.
• They both are in same column $\rightarrow$ then ciphertext is the alphabet right-below the alphabet’s current position. E.g. for “ek” the CT is “ar”
• They both are in different row and column $\rightarrow$ the CT is letter that is in its own row but in the same column as the other letter. E.g. for “th” we look on “t’s” row and “h’s” column i.e. “c”. And for the second letter, we look on “h’s” row and “t’s “column i.e. “f”.