The Shuffling Technique

(Ema_1, Masking/Decryption) – The shuffling technique is a little more complex than the replacement technique, and the symbols remain the same, but after encryption are shuffled. Basically, the shuffling technique can be explained as follows.

For convention and simplicity, the length of the key and blocks is always 16 bytes. This time, in order to observe the substitution in the 16-byte block, we give the source a different value (from “a” to “p” ), namely a=0, b=1, c=2, d=3, e=4, f=5, g=6, h=7, i=8, j=9, k=10, l=11, m=12, n=13, o=14, and p=15.

The algorithm

1. Reads the value of the first byte of the key (index 0)
2. Swaps the element of the data source with index 0 with the element with index the value read in 1.
3. Reads the value of the second byte of the key (index 1)
4. Swaps the data source element at index 1 with the element with index the value read in 3 and so on until the last byte of the last block.

This technique moves the data in the data source out of place, resulting in shuffling. Shuffling is about 20% slower than substitution because it requires more operations on the arrays.

This technique is effective and fast, but it must be used in combination with the replace method, because if it is used alone, you know the symbols of the data source! A solution might be to compress the data source before shuffling.

Note that with this technique, all the bytes of the data source remain unchanged, but are shuffled.

Below is the same example applied to substitution.

KEY & DATA INDEX	KEY VALUES	DATA BEFORE SHUFFLING	SHUFFLING (MASKING)																DATA RESULT
000	006	a	g			d													d
001	007	b		h													l		l
002	015	c			p		e												e
003	000	d				g							f						f
004	002	e					p				b								b
005	009	f						j										c	c
006	013	g	a						n										n
007	008	h		b						i									i
008	004	i								b	p								p
009	010	j						f				k							k
010	003	k										f	g						g
011	012	l												m		a			a
012	014	m												l	o				o
013	011	n							a							m			m
014	001	o													l		h		h
015	005	p			c													j	j
			000	001	002	003	004	005	006	007	008	009	010	011	012	013	014	015

Example of shuffling in masking/encrypting stage

1. key(0)=6; a → data(6), g → data(0)
2. key(1)=7; b → data(7), h → data(1)
3. key(2)=15; c → data(15), p → data(2)
4. key(3)=0; d → data(0), g → data(3)
…

With the shuffling technique we get the highlighted elements [d, l, e, f, b, c, n, i, p, k, g, a, o, m, h, j]). At the computational level, all we need to do is overwrite the elements of an array. Again, Reordering will return the source string.