Feistel encoding

Consider the encryption system below:

Consider the following permutation F of {1, 2, 3}: F(1) = 2, F(2) = 3 and F(3) = 1.

This permutation suggests the following encoding of a 3-letter word: the first letter of the word goes to the second place, the second goes to the third place and the third letter goes to the first place. For example, the world run will be encoded as nru. Suppose we have a longer text whose length is a multiple of 3. Then the encoding is done as follows.

1. The text is divided into 3-letter blocks.

2. Each of the blocks is encoded as specified above.

3. The encoded blocks are joined back together.

For example, the text ilovemath is encoded as follows.

1. The 3-letter blocks of this text are ilo, vem, and, ath.

2. The respective encodings of these blocks are oil, mve and hat.

3. The resulting encoding of the whole text is oilmvehat.

For example, consider the word 010101. Partition the word into blocks of length 3 that are 010 and 101. Then do the forward shift to each of these blocks as specified by the permutation in the explanatory part of the previous question. The first block will become 001 and the second block will become 110. Finally join the blocks to obtain 001110.

Please answer the following questions.

1. Describe a Feistel encryption system whose input is the above encryption algorithm (recall that Feistel encryption is a generic method that uses another encryption system as input).

2. 15 marks. Using the description as in the previous question, encrypt the following plaintext 010101110011.