DESC:FORM – 2

THE PATENTS ACT, 1970
(39 of 1970)
AND
THE PATENTS RULES, 2003

COMPLETE SPECIFICATION

(See Section 10; rule 13)

TITLE OF THE INVENTION

DNA BASED ENCRYPTION METHOD TO PROVIDE HIGH SECURE AND RELIABLE DATA TRANSMISSION

NAME OF THE APPLICANT
INSTITUTE OF AERONAUTICAL ENGINEERING
Dundigal, Hyderabad – 500 043
Telangana, India
An Indian Institute

The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF THE INVENTION
The present invention relates in general to the field of information security in communication transmission and in particular to a DNA based encryption method which is capable of avoiding intruders to obtain original information from cipher text to provide highly secure and reliable data transmission.

BACKGROUND AND PRIOR ART
Computer and Internet Security are very vital in today’s insecure world with the mass of information dissemination, information security and confidential information.
Many encryption algorithms are in existing in the market, but most of them are not reliable and lacking large parallel capacity, large-scale information search, for a large number of information encryption, and very slow in operation. There is much possibility of intercepting the original information from key or password based encrypted information by the expert attacker.
DNA based encryption is a new branch of the development in the present arena due to the large-scale parallelism and ultra-high density storage capacity of DNA molecules. DNA based technique will not only useful for store and transmitting the data, but also to perform various computations. Even it is under primal stage, DNA cryptography is shows extremely efficient. This also offers a unique cipher text generation process as well as a new key generation practice.
There is extensive research going on presently in the field of DNA based encryption methodologies. Although some simple encryption systems based on DNA molecular encryption techniques have been developed so far, it is possible to construct much effective DNA cryptography with different cryptosystems based on different biological difficulties. So, still there is a need to explore new, more complex, secure and more operational cryptographic systems to meet the present requirements in the information security domain.
OBJECTS OF THE INVENTION
Accordingly, the primary object of the invention is to provide a method of DNA based encryption which overcomes the disadvantages/drawbacks of the prior art.
Another object of the present invention is to provide reliable yet effective DNA based encryption to provide high secure data transmission.
A further object of the present invention is to provide an effective and complex DNA based encryption method, so that intruder can’t decode the original information.
How the foregoing objects are achieved will be clear from the following description. In this context it is clarified that the description provided is non-limiting and is only by way of explanation.

SUMMARY OF THE INVENTION
A DNA based encryption method provides high secure and reliable data transmission performed through an algorithm containing two rounds, comprising of the steps of: reading binary bits from sender’s plaintext message; dividing the binary bits into 8-bit blocks; encrypting each block of binary bits; generating round 1 key (Kg); sending every 8-bit block of plain-text to the round 1 encryption by round 1 encryption key (Kg) using CBC method; using the outcome of one block of CBC as the input (key) for the next block; generating 1st level intermediate cipher text; the sender selecting a string of DNA sequence from publicly available DNA sequence source, the DNA sequence being one of the keys of encryption round 2; ensuring that the receiving side has the information about the used DNA sequence; converting this selected DNA sequence into binary string using binary coding scheme; segmenting this binary string into k-bit (Rn-random number) blocks; encrypting the 1st level cipher text using the DNA sequence by inserting each block of the intermediate cipher text before one block of the DNA sequence; repeating the DNA sequence when the length of DNA sequence is less than the length of the intermediate cipher text; removing the extra bit from the DNA sequence when the case is reversed; generating 2nd level cipher text ; and generating final cipher text in DNA sequence form by concatenating all blocks and then converting into a faked DNA sequence called human made DNA sequence using binary coding scheme of DNA.
The round 1 encryption key (Kg) is a computer based random number generated at sender side and shared secret key and the information about the key is sent to the recipient through a secure channel.
The final cipher text has extra information including starting and ending primers that is not linked up with the original message.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The nature and scope of the present invention will be better understood from the accompanying drawing, which is by way of illustration of a preferred embodiment and not by way of any sort of limitation. In the accompanying drawing:-
Figure 1 shows the flow diagram of the method of DNA based encryption according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION
Having described the main features of the invention above, a more detailed and non-limiting description of a preferred embodiment will be given in the following paragraphs with reference to the accompanying drawing.
All through the specification including the claims, the technical terms and abbreviations are to be interpreted in the broadest sense of the respective terms, and include all similar items in the field known by other terms, as may be clear to persons skilled in art. Restriction or limitation if any referred to in the specification, is solely by way of example and understanding the present invention.
Data that can be read and understood without any special measures is called plaintext or clear text. This is the message or data that has to be secured. The method of disguising plaintext in such a way as to hide its substance is called encryption. Encrypting plaintext results in unreadable gibberish called cipher text. Encryption is used to ensure that information is hidden from anyone for whom it is not intended, even those who can see the encrypted data. The process of reverting cipher text to its original plaintext is called decryption.
Cryptography is the science of mathematics to encrypt and decrypt data. Cryptography enables us to store sensitive information or transmit it across insecure networks like Internet so that no one else other the intended recipient can read it. Cryptanalysis is the art of breaking ciphers, that is, retrieving the original message without knowing the proper key. Cryptography deals with all aspects of secure messaging, authentication, digital signatures, electronic money, and other applications.
DNA is a small molecule that encodes genetic information which is very essential for execution and growth of all organisms. DNA stands for Deoxyribo Nucleic Acid. DNA is a polymer made up of monomers called Deoxyribo nucleotides. Every nucleotide consists of three main parts: Deoxyribose, sugar and phosphate group and a nitrogenous base. The nitrogenous bases are Adenine, Guanine, Cytosine and Thymine (“A”,”G”,”C”,”T”). DNA is formed by a double helix which is formed by base pairs attached to a sugar-phosphate backbone.DNA (Deoxyribose Nucleic Acid) computing, also known as molecular computing which is a new approach that provides parallel computation, developed by Adleman. DNA computing was designed for solving a class of difficult computational problems in which the computing time can grow exponentially with problem size (the 'NP- Complete’ or non-deterministic polynomial time complete problem). DNA computer is basically a collection of specially selected DNA strand which all together will result in the solution to some problem, depending on the nature of the problem.
DNA cryptography is a new-promising technology in the area of network security which has emerged with the growth in the DNA computing field. DNA is not only useful for storing and transmitting the data, but also to perform computation. Even though it is in its primal stage, DNA cryptography has shown extreme efficiency. It also offers a unique cipher text generation process, as well as a new key generation practice.
The method according to the present invention teaches a procedure which has two rounds. In the first round, a reference DNA sequence is secretly selected along with a secret Key (SK). The first round generates a secured symmetric key, a secretly selected DNA sequence (s), cipher block chaining mode (CBC) and generates an intermediate form of cipher-text. In the second round, the cipher text is changed into the final cipher text(S). The final cipher-text is converted using a reference DNA Sequence into a faked DNA Sequence called human made DNA Sequence(S’). This faked DNA Sequence is sent to the receiver together with many other DNA, or DNA-like sequences. By this process it becomes more complicated for an intruder to access the original information.
In the first round, plain text or message of the sender is converted into binary form and then divided into 8-bit blocks. Each block of the binary bit is encrypted using round 1 key in Cipher Block Chaining (CBC) mode method. In this, the outcome of one block of CBC is used as the input (key) for the next block. The first level cipher text is generated in this round.
In the second round, the first level cipher text generated from first round is encrypted using a random DNA sequence from publicly available DNA sequences. The selected DNA sequence is converted into binary string using binary coding scheme. This binary string is then segmented into k-bit (Rn-random number) blocks. Each block of the intermediate cipher text is then inserted before each block of the DNA sequence. When the length of DNA sequence is less than the length of the intermediate cipher text, the DNA sequence is repeated. When the case is reversed, the extra bit from the DNA sequence is removed. Next, all blocks are concatenated and then converted into a faked DNA sequence using binary coding scheme of DNA, which is called as human made DNA sequence. This final cipher text has extra information including starting and ending primers that is not linked up with the original message.
The final cipher text is sent to the receiver. The first round 1 key and selected DNA sequence are shared with the receiver through a secure channel before the communication takes place to decrypt the original message from final cipher text.

Methodology
The present invention discloses a new method of encryption process in order to provide high security and reliable data transmission. As mentioned before, the method is performed through an algorithm containing two rounds which work on the binary values read from the plaintext. A session key, a random number and DNA sequence are handed over through a secure channel between sender and receiver before the communication takes place. The session key bears the information about the key that is used for encrypting the message. The key which is used in round 1 for encryption is calculated based on a number generated randomly and the information about the key is sent to the recipient through a secure channel. Round 1 encryption key (Kg) is a computer based random number generated at sender side and shared secret key. After that every 8-bit block of plain-text is sent to the round 1 encryption by round 1 encryption key (Kg) using Cipher Block Chaining mode (CBC) method. The outcome of one block of CBC is used as the input (key) for the next block.
In encryption round 2, the sender selects a DNA sequence randomly from publicly available DNA sequences. This DNA sequence is one of the keys of encryption round 2. The receiving side must have the information about the used DNA sequence. This selected DNA sequence is then converted into binary string using binary coding scheme. This binary string is then segmented into k-bit (Rn-random number) blocks. Each block of the intermediate cipher text is inserted before one block of the DNA sequence. When the length of DNA sequence is less than the length of the intermediate cipher text, the DNA sequence is repeated. And when the case is reversed then the extra bit from the DNA sequence is removed. After that all blocks are concatenated and then converted into a faked DNA sequence called human made DNA sequence using binary coding scheme of DNA. This final cipher text has extra information including starting and ending primers that is not linked up with the original message.
Algorithm-1 for implementing Encryption
Steps for Encryption (Round 1)
Step 1: Conversion from Plain text to binary bits
Read Binary bits from Plaintext and divide into 8 bit blocks.
Step 2: Generate a Common secrete Key (SK)
1. Define a common secret key (SK) (by using Random Generator)
2. Select DNA Sequence
3. Select Complementary Rules
4. Select DNA Binary coding Rules
5. All are shared between sender and receiver prior to communication (16-bit).
Step 3: Compute Session Key (KS).
Compute Session Key based on secret key and Random Number (Rn)
Step 4: Compute Encryption Key for Encryption (KE)
Step 5: Compute 1st Level Cipher Text
Generate: Level 1 cipher Text by Performing XOR Operation on Step 1 and Step 2.
Steps for Encryption (Round 2)
Step 1: Select DNA sequence (S).
Code S into a binary sequence by using the binary coding scheme.Divide S into segments whereby each segment contains k bits. (Select k randomly).
Step 2: 1. Divide the First level cipher text into k bits (FCT) block.
Step 3: Encrypt the DNA Sequence
Insert bits from (FCT), once at a time, into the beginning of segments of S.
Concatenating the above segments.
Use the binary code scheme to convert the above segments into faked DNA sequences and add extra information.

Algorithm-2 for Session Key Generation and Sharing
Define A common secret key (PK) is shared between sender and receiver prior to communication. (16-bit).
1) Sending End Computations:
Step 1
Sender will use a random number generator and select one random number which is of 16-bit (Rn).
Step-2
Divide the random number ‘Rn’ into 2 parts each of having 8-bit. (RnL and RnR)
Step-3
Divide the shared secret key into 2 parts as PKL and PKR. Both of these are of 8-bit.
Step-4
Now PKL will get X-OR with RnR and PKR will get X-OR with RnL.
RL= PKL ? RnR RR= PKR ? RnL
Step-5
Both of the results will be further sub-divided into 2 parts namely RL1, RL2 and RR1, RR2 having 4-bit each.
Step-6
Make 4 bit EX-OR Operation between RL1 and RL2 and between RL2 and RL1.
T1=RL1 ? RR2 T2=RL2 ? RR1
Step-7
Concatenate these 4-bit results, T1 and T2, which will give Encryption key of 8-bit for round 1.
KE = K1= concate(T1,T2)
Step-8: Session key computation for round1
Compute, tmp= PK ? Rn
Session key computation
tmp= PK ? Rn = 49429 ? 6255 = 55674 KS1= 55674 % 16 = 10 = A (hex form)
tmp= 55674 / 16 = 3479 KS2= 3479 % 16 = 7 = 7 (hex form)
tmp= 3479 / 16 = 217 KS3= 217 % 16 = 9 = 9 (hex form)
tmp=217 /16 = 13 KS4 = 13 = D (hex form) Session key,
KS = A79D
Step-9
: Divide ‘tmp’ by 16 and convert the remainder into its equivalent hex form and keep it in ‘KS1’
Divide the result once again by 16, keeping hex form of the remainder. in ‘KS2’.Do until the result is less than 16 (KS3, KS4…... KSn).
Step-10
Make together all the ‘KSs’ in order to get the round 1 session key
KS
Step-11 Send ‘KS’ as round 1 session key through a secure channel along with round 2’s session key.
End

2) Receiving End Computations
Input: Shared secret key ‘PK’ and session key ‘KS’
Step-1 Separate all the digits of ‘KS’ and convert these into their equivalent decimal form
e.g. KS = A79D (say), KS1=10, KS2=7, KS3=9, KS4=13
Step-2 Computation of decryption key as follows:
tmp = KSn
tmp = (tmp*16) + KSn-1 continue upto KS1
Random number, Rn = tmp ? PK
e.g. tmp1 = (13 * 16) + 9 = 217
tmp2 = (217 * 16) + 7 = 3479
tmp = tmp3 = (3479 *16) + 10 = 55674
Rn = (49429 ? 55674) = 6255
Step-3: Divide the random number ‘Rn’ into 2 parts each of having 8-bit. (RnL and RnR) and divide the shared secret key into 2 parts as PKL and PKR. Both of these are of 8-bit.
Step-4: Now PKL will get X-OR with RnR and PKR will get X-OR with RnL.
RL= PKL ? RnR RR= PKR ? RnL
RL=193 ? 111 = 174 RR = 21 ? 24 = 13
Step-5: Both of the results will be further sub-divided into 2 parts namely RL1, RL2 and RR1, RR2 having 4-bit each.
Step-6: Make 4-bit EX-OR operation between RL1 and RR2 and between RL2 and RR1
T1=RL1 ? RR2 T2=RL2 ? RR1
T1=10 ? 13 = 7 T2= 14 ? 0 =14
Step-7: Concatenate these 4-bit results, T1 and T2, which will give Decryption key of 8-bit for round 1.
K1= concate(T1,T2)
Decryption key, KD= K1= concate (0111, 1110) = 01111110 = 126
End.
Procedure for Key Sharing for Round 2
Generate a number randomly that will be used as round 2 key for the second round of encryption process. This key will give the size of extra bit that is to be added with the cipher text, to make the cipher text more complicated to the intruders. Select a DNA sequence randomly from publicly available DNA sequences. The round key 2 and the selected DNA sequence are to be sent at the receiver end prior to communication.
In encryption round 2, sender will select a DNA sequence randomly from publicly available DNA sequences. This DNA sequence is one of the key of encryption round 2. Receiving side must have the information about the used DNA sequence.
The present invention has been described with reference to some drawings and a preferred embodiment purely for the sake of understanding and not by way of any limitation and the present invention includes all legitimate developments within the scope of what has been described herein before and claimed in the appended claims.
,CLAIMS:We claim:
1. A DNA based encryption method to provide high secure and reliable data transmission performed through an algorithm containing two rounds, comprising of the steps of:

- reading binary bits from sender’s plaintext message;
- dividing the binary bits into 8-bit blocks;
- encrypting each block of binary bits;
- generating round 1 key (Kg);
- sending every 8-bit block of plain-text to the round 1 encryption by round 1 encryption key (Kg) using CBC method;
- using the outcome of one block of CBC as the input (key) for the next block;
- generating 1st level intermediate cipher text;
- the sender selecting a string of DNA sequence from publicly available DNA sequence source, the DNA sequence being one of the keys of encryption round 2;
- ensuring that the receiving side has the information about the used DNA sequence;
- converting this selected DNA sequence into binary string using binary coding scheme;
- segmenting this binary string into k-bit (Rn-random number) blocks;
- encrypting the 1st level cipher text using the DNA sequence by inserting each block of the intermediate cipher text before one block of the DNA sequence;
- repeating the DNA sequence when the length of DNA sequence is less than the length of the intermediate cipher text;
- removing the extra bit from the DNA sequence when the case is reversed;
- generating 2nd level cipher text ; and
- generating final cipher text in DNA sequence form by concatenating all blocks and then converting into a faked DNA sequence called human made DNA sequence using binary coding scheme of DNA.

2. The DNA based encryption method as claimed in claim 1, wherein said round 1 encryption key (Kg) is a computer based random number generated at sender side and shared secret key and the information about the key is sent to the recipient through a secure channel.

3. The DNA based encryption method as claimed in claim 1, wherein said final cipher text has extra information including starting and ending primers that is not linked up with the original message.

Dated this on 26th day of March, 2018

Subhajit Saha
Patent Agent (IN/PA-1937)
Agent for the applicant