On Couple Magic Total Labellings of Graphs for Designing New Graphical Cryptographs

New passwords obtained by an idea of "graphical construction plus number theory" could be easy than other graphical passwords in storage space and communication of information. We show two examples for illustrating this idea, and design a new graph labelling, called (k
⁺
, k
^-
)-couple edge- magic total labelling, for realizing possibly this idea. We then present some theoretical algorithms for building graphical constructions having our labellings, and propose some new labellings and problems, such as "Every simple graph admits a 〈(k
_i
⁺
)
₁
^s
, (k
_j
^-
)
₁
^t
〉-CEMTL", for further deep research in graph labellings and graphical passwords.