DES | Assymetric Key

DES Attack à man in the middle attack

Sender …DES encrypted message + key by hacker ….Receiver

IDEA àInternational Data Encryption Standard (Commercial Version)

Input   : 128 bits

Key     : 128 bits

Output: 128 bits

To get down encryption it take 8 rounds

For doing email encryption is using PGPà Pretty good privacy

RC-5 à Rivest Cipher / Smart Card

AES à Advanced Encryption Standard

Input : 128 bits or 256 bits

Key: 128 bits or 256 bits

Output : 128 bits or 256 bits

Week 4 Day 5 – ITEC Programme

AXCRYPTà Encryptionà EAS

 For Securing key exchange there is save way to do it using Diffie Hellman Key Exchange or Agreement.

Sender ------à------ Receiver

Step 1 : 1^st sender & receiver agree upon two large prime numbers

Step 2 : Sender choses another large random number.

Ex : it is X

Such that sender calculate A= g ^x mod n

Step 3 : This A is sent to receiver

Step 4 : At the receiver end, receiver also chooses large random number that is suppose Y

And calculate B such that B= g ^y mod n

Step 5 : Receiver sends B to sender

Step 6 : Sender calculates the key as K₁= B ^x mod n

Step 7 : Receiver calculates the key as K₂=A ^y mod n so K=K₁=K₂

Example

Step 1 : Let n=11 g=7

Step 2 : ender chooses x  suppose x =3

Step 3 : A=g ^x mod n

                 =7 ³ mod 11

                 = 2

Step 4 : suppose y= 6 and B =4

              B = g ^y mod n

                  = 7 ⁶ mod 11

                  = 4

Step 5 : B will be sent to sender

Step 6 : Sender calculates key value

             K₁ = B ^x mod n

                  = 4 ³ mod 11

                  = 9

Step 7 : Receiver end calculate key value

             K₂ = A ^y mod n

                  = 2⁶ mod 11

                  = 9

            K = k ₁ = k ₂

Assymetric Key

Assymetric Keyà Same Key (Encryption & Decryption)

Assymetric Key à Public Key (Known to all)  and Private key (Remind private or an individual)

Public Key à Encryption, Private Key à Decryption

But if the aim is authentication

Private Key à Encryption, Public Key à Decryption

RSA Algorithm

Working of RSA

Step 1 : Change two large prime numbers , suppose P & Q

Step 2 : Calculate N= P.Q

Step 3 : Select the public key E such that it shared not be the factor of (p-1) (q-1)

Step 4 : Encryption is given by

              C= (PT) ^E mod n

              Where  C =Cipher text

                           PT = Plain text

                            E = Public key

                            N = P.Q

Step 5 : The private key D should be chosen by receiver such that

              (D.E) mod (P-1).(Q-1) = 1

Step 6 : Decryption

             PT = C ^D mod n

              D = Private key

              C = Cipher text

              PT= Plain text

Example :

Step 1 : suppose P=7 Q = 17

Step 2 : n = p. q

                = 7 . 17

                = 119

Step 3 : E such that (p-1) (q-1)

               (p-1) (q-1) = 6.16 = 96

               Suppose E= 5 bcoz 6=1,2,3,6 (6 can be devided by numbers written beside)

               And 16 (1,2,4,8,16) /prime #. So choose which is not there.

Step 4 : C=(PT) E mod N

                = (10) 5 mod 119

                = 40

Step 5 : (D.E) mod (P-1) . (Q-1) =1

              (D.5) mod 96 = 1

              To figure out D à 96 . 4 = 384 + 1 = 385 / 5 = 77

              (D.5) mod 96 = 1

              (77.5) mod 97 = 1

Step 6 : Decryption

             PT = C ^D mod n

                  = 40 ⁷⁷ mod 119

                  = 10