  This work proposes a different procedure to encrypt images of 256 grey levels
and colour, using the symmetric system Advanced Encryption Standard with a
variable permutation in the first round, after the x-or operation. Variable
permutation means using a different one for each input block of 128 bits. In
this vein, an algorithm is constructed that defines a Bijective function
between sets Nm = {n in N, 0 <= n < fac(m)} with n >= 2 and Pm = {pi, pi is a
permutation of 0, 1, ..., m-1}. This algorithm calculates permutations on 128
positions with 127 known constants. The transcendental numbers are used to
select the 127 constants in a pseudo-random way. The proposed encryption
quality is evaluated by the following criteria: Correlation; horizontal,
vertical and diagonal, Entropy and Discrete Fourier Transform. The latter uses
the NIST standard 800-22. Also, a sensitivity analysis was performed in
encrypted figures. Furthermore, an additional test is proposed which considers
the distribution of 256 shades of the three colours; red, green and blue for
colour images. On the other hand, it is important to mention that the images
are encrypted without loss of information because many banking companies and
some safety area countries do not allow the figures to go through a compression
process with information loss. i.e., it is forbidden to use formats such as
JPEG.
