PROJECT- DATA ENCRYPTION STANDARD
 
AIM- ENCRYPTION AND DECRYPTION OF DATA USING DES ALGORITHM.

SUMMERY OF THE PROJECT-

***What is Data encryption standard?***
The DES is a symmetric block cipher that makes use of only one key for encrypting and decrypting the 64-bits block of     
plaintext into 64-bit block of ciphertext using 56-bits key.


***Processing of Data Encryption Standard?***
DES encryption algorithm consists of three parts which are as follows-
1.Right hand side process- Key generation
2.Middle one process- Way in which Plaintext processing. 
3.Left hand side process- Structure of a single round of operation.


***What operations we have to do in these three processes plaintext encryption?***
For Key generation Operation-
1.Permuted Choice1- Converting inserted 8 character of key into 64-bit binary , removing multiples of 8 form 64-bit key and reducing it into 56-    
                    bit key.
2.Left Circular shift- Dividing 56-bit key into two halves and if the round no are 2,9 or 16 we will shift that round no by one elsewhere by     
                       two.
3.Permuted Choice2- Here it will give both left circular shifted values as input and remove this index list elements to convert 56-bit key into                     
                    48-bit key [9, 18, 22, 25, 35, 38, 43, 54].


For 16 Round of operation-
1.Expansion- Generating expansion table and expanding R0's 32-bit into 48-bit. 
2.XOR operation with corresponding round subkey- Performing the XOR operation between expanded 48-bit (generated by expansion table) and 48-bit                  
                                                 subkey which is generated by key generation. 
3.Substitution- S-box consist of eight S-boxes represented as 4*16 matrix in which each S-box receives 6 bits as input and produces 4-bit as 
                output.So eight S-box produce a total 32-bits.
4.Permutation- Produced 32-bits from substitution operation mapped with the permutation table.

Way of Plaintext processing-
1. Initial Permutation- First Plaintext converted into ASCII value then ASCII value converted into the binary values and then mapped it with 
                        initial permutation table. 
2. 16 Round of operation- Here we will perform expansion, XOR operation, substitution, permutation operations.
3. 32-bits swap- Interchanging the Ri and Li values.
4.Inverse initial permutation- reversing the initial permutation process.
 
***How to decrypt the ciphertext into plaintext?***
1. Initial Permutation
2. 16 Round of operation using key in reverse order
3. Inverse initial permutation