step 1)

Take the plaintext, and perform a columnar transposition using the given keyword.

3 5 1 4 2 6 C E A D B F t h i s i s a n e x a m p l e

result: I E E I A T A P S X H N L S M

step 2)

Form a square as close to "regular" as possible (2x2, 3x3, etc.), padding as necessary.

I E E I A T A P S X H N L S M E

step 3)

Rotate the square clockwise according to the value specified in the key (ex: 90 degrees).

L S A I S X T E M H A E E N P I

step 4)

Perform a second columnar transposition using the third keyword.

2 1 3 B A C L S A I S X T E M H A E E N P I

final ciphertext: S S E A N L I T H E I A X M E P