Page 14 - 2024-Vol20-Issue2

10 | Yousif, Hameed & Al-Zuhairi

(a) (b) (c)

(d) (e) (f)

Fig. 6. Correlation of Neighbor Pixels for Lena Image (a) and (d) in Horizontal Direction for Plain and Cipher Images,
Respectively (b) and (e) in Vertical Direction for Plain and Cipher Images, Respectively (c) and (f) in Diagonal Direction for
Plain and Cipher Images, Respectively

values are quite low between the plaintext and encrypted im- UACI = 1 |C1(i, j) -C2(i, j)| × 100% (14)
ages, which exhibits that the TIC can encrypt images with ×
high quality. ?i, j 255

M N

B. Differential Analysis D(i) = 0 if C1(i, j) = C2(i, j) (15)
1 if C1(i, j) ?= C2(i, j)
One of the most desired attributes in an image ciphering sys-
tem is its sensibility level to a trivial alteration in the plaintext where C1 and C2 indicate the to two ciphered images whose
image. An adversary usually tries to make tenuous modifica- corresponding plain images with only one-pixel difference, M
tion in the input image such as changing only one pixel and and N represent the width and height, respectively of C1 or C2.
then monitoring the alteration in the output ciphered image. For grayscale image, the optimal values for UACI and NPCR
The adversary expects by this way to find a beneficial rela- are: 33.4635 % and 99.6094 %, respectively [20, 41–44]. The
tion between the input image and the encrypted image. If a UACI and NPCR results generated via the TIC are reported
slight alteration in the original image yields a totally different in Table II. It can be observed from this table that all obtained
cipher image, then the differential analysis will be virtually NPCR and UACI values are close to the expected values. This
infeasible. Number of Pixel Change Rate (NPCR) and Uni- demonstrates that the TIC possesses an extreme sensibility to
fied Average Changing Intensity (UACI) are the two common pixel modulation in the original image and therefore it can
criteria utilized to examine the impact of changing one pixel effectively counter the differential attack.
on the ciphered image. These two criteria are given as:

NPCR = ?i, j D(i, j) × 100% (13)
M×N