*2.2.3 Encryption*

Another technique that can be combined with DES is "hybrid graphical encryp-

The rest of this chapter is organized as follows. Section 2 describes DNA hybridization encryption scheme in detail. This section also presents performance analysis of algorithms and methods used by DHES. Similarly, Section 3 presents hybrid graphical encryption with illustrations. This section also presents performance analysis of encryption and decryption algorithms used by HGEA by comparing it

DNA cryptography is an emerging field of cryptography that deals with hiding data in terms of DNA sequences [10, 11]. It can be implemented by using modern biological techniques as tools and DNA as information carrier to fully exert the inherent advantage of high storage density and high parallelism to achieve encryption [12]. The DNA cryptography uses the concept of molecular approach in tradi-

Some terminologies used in biochemical operations of DNA cryptography are annealing, melting, ligation, amplification, cutting, gel electrophoresis, oligonucle-

DNA hybridization is a process in which two single-stranded DNAs (ssDNAs) are combined together to produce a single DNA sequence [15]. The two ssDNAs are complementary to each other and are of same length. That means: if one strand of

the pairs fails and fragmentation occurs. To remove such fragmentation, fragment

OTP is the only potentially unbreakable encryption method. Plaintext encrypted using an OTP cannot be retrieved without the encryption key. The key generated by an OTP must be random and generated by a non-deterministic, non-repeatable process. The key also must be never re-used. In OTP scheme, the length of the key

OTP is used for key generation. The generated key is unique and only the sender and receiver know the key and that generated key is destroyed once it is used. The key generated by computers is not truly random; so, a pseudorandom number generator function is used for generating the key and the generated key is in the DNA. The size of ssDNA key is greater than the original size of the message, which results in

, then the other strand must be 500. If not, then the hybridization of

tion algorithms (HGEA), which is based on graphical interpretation by pattern recognition and transformation like hybrid cubes encryption algorithm (HiSea) [8, 9]. Most of the graphical encryption algorithms use mono-alphabetic or polyalphabetic substitution and their range of input values is limited. But, HGEA uses a range of characters consisting of 256 possible values. It also produces output of 256 characters for single-input plaintext. Moreover, HGEA can be used by software as

well as realized by implementing hardware devices.

**2. DNA hybridization encryption scheme (DHES)**

tional cryptographic technique to make the system more secure.

must be greater than or equal to the length of the plaintext.

with that of DES.

**2.1 DNA cryptography**

*Computer and Network Security*

otides, etc. [13, 14].

DNA is 3<sup>0</sup> to 5<sup>0</sup>

*2.2.1 OTP scheme*

*2.2.2 Key generation*

**142**

**2.2 DNA hybridization**

assembly has to be done [16].

The encryption process consists of the following steps (**Figure 1**):

	- If the first digit of binary bit is 1, then this bit is compared with last n bases of OTP key and complementary data of DNA form are produced as the encrypted message where n is the number of bits required to represent the nucleotides.

**Figure 1.** *Flow chart of DNA hybridization encryption.*

*2.2.5 DDHO algorithm*

*Hybrid Approaches to Block Cipher*

*DOI: http://dx.doi.org/10.5772/intechopen.82272*

left and right halves.

above step.

each nucleotide.

find the occurrences of 0 and 1 s.

to obtain the resulting ciphertext.

the nucleotides.

encryption algorithm.

*2.2.6 Analysis of DDHO*

**145**

Here, the proposed algorithm DDHO (combination of DES algorithm and DNAbased hybridization and OTP scheme) is explained in detail. First, the DES algorithm is performed on the given plaintext and key and the resultant ciphertext is taken as an input to the DNA hybridization and OTP scheme. Further, the algorithm proceeds as per the above illustrated DNA hybridization and OTP scheme.

1. A block of 64 bits is permutated by an initial permutation called IP.

3. The right half goes through a function F (Feistel function)

5. The left and right halves are swapped (except the last round).

the last step which produces a ciphertext in binary form.

2. Resulting 64 bits are divided into two equal halves, each containing 32 bits,

4.The left half is XOR-ed with output from the F function obtained in the

6. In the last round, apply an inverse permutation (IP-1) on both halves that is

7. The ssDNA OTP key is generated and the length of this key depends upon the length of binary plaintext and the number of bits required to represent

8. Start scanning the binary sequence, obtained in step 6, from left to right to

• If first digit of binary bit is 1, then this bit is compared with last n bases of OTP key and complementary data of DNA form are produced as the encrypted message where n is the number of bits required to represent

• If the first digit of the binary bit is 0, then no operation is carried out and the next n bases in the OTP key from reverse order are ignored where n is the number of bits required to represent nucleotides.

9.Repeat step 8 for all the occurrences of 1 and 0 s and put them all together

The plaintexts chosen for encryption and decryption using the DDHO algorithm are highly diverse. They include short and long texts, purely alphabetical text and text containing alphabets and many other characters. The plaintexts of diverse types are selected, so that they are very representative. With regard to difference of the lengths of the text, four plaintexts with increasing size are selected (**Table 1**).

The decryption algorithm of DDHO is the reverse process of DDHO

The encryption algorithm for DDHO is as follows:

#### **Figure 2.**

*Flow chart of DNA hybridization decryption.*

