Note that (1) the 8-bit grayscale image Lena of size 256x256 pixels is used; (2) the speed of each image encryption/decryption system excludes that of key stream generator; (3) the scheme of AES uses a secret key of length 256 bits ; (4) the scheme in  uses a secret key of length 256 bits; (5) the scheme in  uses three double-precision floating-point numbers as the secret key (equivalent to the key length
of 140 bits); (6) the scheme in  uses four double-precision floating-point numbers as the secret key (equivalent to the key length
of 186 bits); (7) the values of NPCR and UACI are the average values of 100 tests.
One advantage of using the proposed algorithm compared to the previous algorithm, for example in , is that its flexibility to choose the secret key length
(3) The encryption and decryption support very long key, and the influence of the key length
to the compression/encryption time can be ignored.
In AES, each 128-bit data block undergoes 10-14 rounds (depending on key length
) of permutations, substitutions, and additions .
The design and strength of all key lengths
of the AES algorithm are sufficient to protect classified information.
In IDEA, the block length is 64-bit and master key length
Equation (7) is written such that 90 % of results obtained are greater than the desired final key length
(A) while remaining very close to this value, as shown in Fig.
DES cipher is generally considered unsafe due to its key length
which is only 56 bits, making brute force attack on cipher feasible.
Encryption can be done by different methods depending on the algorithm and key length
When a key length
is 256 bits, the cipher key space is [2.sup.256] [approximately equal to] 1.16 * [10.sup.77].) It can achieve the confidential requirement.
The TMP exception applies to symmetric commercial-grade encryption with a key length
of fewer than 64 bits.