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Table 5 Symbols used in depicting Fig. 2. For simplicities, we denote 0000 by 0 and arbitrary four bits by ?

From: Searching for impossible subspace trails and improved impossible differential characteristics for SIMON-like block ciphers

Symbol

Description

Dimension

U0

(1***| ?| ?|?,?| ?| ?|?)

31

U1

(?| ?| ?|?,1***| ?| ?|?)

31

\(U_{2}^{0}\)

(1***| ?| ?|?,*00*| ?|0*** |?)

28

\(U_{2}^{1}\)

(0***| ?| ?|?,*01*| ?|0*** |?)

28

\(U_{3}^{0}\)

(*01*| ?|0*** |?,0*00 |0*** |*00* |?)

23

\(U_{3}^{1}\)

(*00*| ?|0*** |?,0*00 |1*** |*00* |?)

23

\(U_{4}^{0}\)

(0*00 |1*** |*00* |?,*000 |000* |0*00 |0***)

16

\(U_{4}^{1}\)

(0*00 |0*** |*00* |?,*000 |001* |0*00 |0***)

16

\(U_{5}^{0}\)

(*000 |001* |0*00 |0***,0*00 |0|0|000*)

8

\(U_{5}^{1}\)

(*000 |000* |0*00 |0***,0*00 |0|1000|000*)

8

U6

(0*00 |0|1000|000*, 0|0|0|0)

2