logging in or signing up cryptography meetujain Download Post to : URL : Related Presentations : Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Uploaded from authorPOINT lite Insert YouTube videos in PowerPont slides with aS Desktop Copy embed code: (To copy code, click on the text box) Embed: URL: Thumbnail: WordPress Embed Customize Embed The presentation is successfully added In Your Favorites. Views: 1516 Category: Education License: All Rights Reserved Like it (4) Dislike it (0) Added: April 11, 2010 This Presentation is Public Favorites: 4 Presentation Description plz gv me ur i'd toooo Comments Posting comment... By: Fatzz (15 month(s) ago) can any1 plz mail me dis presetation.........plz.......... Saving..... Post Reply Close Saving..... Edit Comment Close By: meetujain (15 month(s) ago) asshokuim....... plz mail me ut correct id dear......... Saving..... Post Reply Close Saving..... Edit Comment Close By: asshokuim (15 month(s) ago) please send this ppt to my email id-asshokuim@gmail.com, I will be very thankful to u. Saving..... Post Reply Close Saving..... Edit Comment Close By: pintukumari (15 month(s) ago) ur slides are very very gud n i like them. so can u plz send me this ppt on my e mail id today itself i need them vey urgently .my id is gajbhiyepreeti4@gmail.com.thankz............ Saving..... Post Reply Close Saving..... Post Reply Close Saving..... Edit Comment Close By: meetujain (19 month(s) ago) gv me ur id yar.................. Saving..... Post Reply Close Saving..... Edit Comment Close loading.... See all Premium member Presentation Transcript Presentation oncryptography : Presentation oncryptography shaveta cryptography : cryptography Is a science of secret writing It’s a science and art of transforming messages to make them secure and immune to attacks Slide 3: sender receiver Intruder (unauthorized user) Plain text interrupts Slide 4: Plain text is original message After message is transformed it is called cipher text An encryption algorithm transfers plain text into cipher text using key A decryption algorithm transforms cipher text back into plain text using key. Cipher is defined as an encryption/decryption algorithm Key is number (set of number), that cipher as an algorithm operates on plain text Alice is a person who needs to send data Bob is receiver of data Eve is person who some how disturb the communication between Alice and bob Cryptography components : Cryptography components sender receiver Encryption (using encryption key) Decryption Using decryption key) Plain text Cipher text Plain text Are plain text, algorithms, cipher text Categories of cryptography : Categories of cryptography cryptography Symmetric-key Asymmetric-key Symmetric key cryptography is also called secret key Asymmetric key cryptography is also called public key Secret key Public key Keys and their types : Keys and their types Secret key is shared key used in symmetric-key cryptography Public key and private key are used in asymmetric-key cryptography Symmetric-key cryptography : Symmetric-key cryptography bob Alice encryption decryption Shared secret key Cipher text Here same key is used by sender for encryption and receiver (for decryption) The key is shared ( same key locks and unlocks box) Asymmetric-key cryptography : Asymmetric-key cryptography Alice bob encryption decryption Bobs Private key Bobs Public key It has 2 keys ;private and public ; alice uses public key to encrypt the message, private key is used by bob to decrypt message. Plain text Cipher text Plain text To the public Traditional ciphers : Traditional ciphers Traditional ciphers Substitution ciphers Transposition ciphers Mono alphabetic Poly alphabetic (are character oriented) Slide 11: Substitution cipher substitute one symbol with another for example it replaces a with d and t with z In mono alphabetic cipher a character in plain text is always changed to same character in cipher text for example in hello each and every time l is used it would be converted to d . Relation between character in plain text and cipher text is one to one relation In poly alphabetic cipher ,each occurrence of character can have different substitute one to many relation Substitution cipher and its types Slide 12: Shift cipher-:the simplest mono alphabetic cipher is shift cipher. in it encryption algorithm is ”shift key characters down” with key equal to number. the decryption algorithm is" shift key characters up” For example use shift cipher with key =15 to encrypt message hello Sol:- we encrypt one character at a time. each character is shifted 15 characters down. letter h is encrypted to w ;l to a ;e to t ;l to a ;l to a; O to d. cipher text is wtaad. Slide 13: Transposition cipher:-in it there is no substitution of characters ;instead their locations are changed Reorder (upward direction) Reorder (downward direction) Plain text (block) encryption Decryption Cipher text (block) Plain text (block) 1 2 3 4 1 2 3 4 (3142) Slide 14: X o r cipher:-it is made of set of simple ciphers .it uses exclusive-or-operation. input output An xor operation needs two data input First as plain text and second as key In other words one input is block to be encrypted ,other input is key Exclusive or X=a + b Or x=a’b+ ab’ Slide 15: Rotation cipher:-in it input bits are rotated to left or right. it can be keyed or keyless, in keyed rotation value of key defines number of rotation In keyless rotation number of rotation is fixed (special case of transposition cipher) 1 2 3 4 1 2 3 4 Substitution cipher (s-box):-the input to an s-box is stream of bits with length n ;the result is another stream of bits with length m .it is normally keyless sand is used in intermediate stage of encryption or decryption. A function that matches n input to m output N input bits M output bits Slide 16: Transposition cipher( p-box): it performs transposition at bit level ;it transposes bits .it can be implemented in software or hardware but hardware is faster .p-boxes are keyless there are three types of permutations in p-boxes In straight p-box there are same number of inputs as outputs In expansion p-box the number of output ports is greater than number of input ports Slide 17: In compression permutation cipher ,the number of output port is less than number of input ports Than comes modern round ciphers ;they involve multiple rounds ,where each round is complex cipher made of simple ciphers. the key used in each round is subset or variation of general key called round key if the cipher has n rounds the key generator produces and keys,k1,k2---kn Slide 18: Initial permutation Round 1 Round 2 Round 3 Final permutation round key generator K1 K2 K3 64 bit plain text 64 bit cipher text 64 bit key D E S Slide 19: 64 Bit plain text Encrypt D E S Decrypt D E S Encrypt D E S Decrypt D E S Encrypt D E S Decrypt D E S 64 Bit plain text 64 bit cipher text 64 bit plain text 64 bit cipher text Key 1 Key 2 Key 3 Key 1 key2 Key 3 Encryption triple D E S Decryption triple D E S TRIPLE D E S Slide 20: ROUND KEY GENERATOR ROUND1 ROUND 2 ROUND 10 + 128 BIT KEY K0 K1 128 BIT PLAIN TEXT 128 BIT CIPHER TEXT A E S K 2 K 10 Asymmetric-key cryptography : Asymmetric-key cryptography It has two keys :one private and one public In it two algorithms used are RSA and diffie-hellman RSA The most common public key algorithm is RSA , named for its inventors RIVEST,SHAMIR,ADLEMAN .It uses two numbers ,e and d ,as public and private key Selecting keys : Selecting keys Bob uses following steps to select the private and public keys Bob chooses two numbers p and q Bob multiplies above two prime numbers to get n (n=p*q) Bob calculates number =(p-1)*(q-1) Bob chooses random number e and calculates d so that d*e=1 mod phi Bob announces e and n to public He keep secret phi and d. RSA : RSA Alice C= pe mod n Calculating e ,d ,n bob p= cd mod n public e Plain text Cipher text encryption decryption Plain text private d Slide 24: encryption-:any one who needs to send message to bob can use n and e .for example if Alice needs to send message to bob, she can change message usually a short one ,to an integer. this is a plain text. she can then calculate cipher text ,using e and n. c=pe (mod n) Alice sends c, the cipher text to bob. Decryption-:bob keeps d as private. when he receives cipher text ;he uses his private key d to decrypt the message p=cd (mod n) Slide 25: example:-bob chooses p=7 and q=11 and calculates n=7*11=77 the value of phi =(7-1)*(11-1)=60.now he chooses two keys e ,d .e=13,d=37.now imagine alice sends plain text 5 to bob .she uses public key 13 to encrypt 5 Solution:-plaintext:5 c=pe (mod n)=513 (mod 77)=26 cipher text=26 Bob receives cipher text 26 and uses private keys 37 to decipher the cipher text. cipher text:26 P=cd (mod n) =2637(mod 77) Plain text=5 Slide 26: Diffie hellman was originally designed for key exchange. in diffie hell man crypto system ;two parties create a symmetric session key to exchange data without having to remember or store for future use. two parties needs to choose two numbers p and g . The first number p is a large prime number and second number is random number. p, g are public. Slide 27: Diffie hellman method Alice bob R1=gX mod p R2=gy mod p R1 R2 K=(R2)Xmod p K=(R1)Ymod p Shared secret key K=gxy mod p The value of p and g are public Slide 28: Step 1:l Alice chooses large random number x and calculates R1=gx mod p. Step 2:bob choses another large randon number y and calculates R2=gy mod p Step 3:alice sends R1 to bob (ALICE DOESNOT SENDS VALUE OF X;SHE ONLY SENDS R1) STEP 4:Bob sends R2 to Alice (BOB DOESNOT SENDS VALUE OF Y;HE SENDS ONLY R2) Step 5: Alice sends k=(R2)Xmod p. Step 6: bob also calculates k=(R1) Y mod p. The shared key in diffie hell man protocol is k=gxy mod p. Slide 29: Alice bob g g x y g g x y g y x g One third of key is public She sends key to bob He sends key to Alice The two keys are same because it does not matter if x is filled first or y Alice complete key by adding last part Bob complete key by adding last part Alice and bob fills up another one-third of secret key using her random number Slide 30: Alice Eve bob R1=gx mod p R1 R2=gz mod p R3=gy mod p R2 K1=(R2)Xmod p R2 K1=(R1)Z mod p K2=(R3)Z mod p K2=(R2)Y mod p R3 Alice- eve key Eve-bob key K1=gxz mod p K2=gzy mod p Man in middle attack Slide 31: The following happens 1. Alice chooses x calculates R1=gx mod p ,and sends R1to bob. 2. eve the intruder, intercepts R1.she chooses z ,calculates R2=gz mod p; and sends R2to both Alice and bob. bob chooses y, calculates R3=gy mod p ,and sends R3 to Alice;R3 is intercepted by eve and never reaches Alice. 4. Alice and eve calculate k1=gxz mod p, which becomes a shared key between Alice and eve .Alice, however, thinks that it is a key shared between bob and herself. 5. Eve and bob calculate k2=gzy mod p, which becomes a shared key between eve and bob. Bob, however ,thinks that it is a key shared between Alice and himself. It is also known as bucket bridge attack because it resembles a short line of volunteers passing a bucket of water from person to person Slide 32: THANKS Slide 33: ANY QUERIES You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.
cryptography meetujain Download Post to : URL : Related Presentations : Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Uploaded from authorPOINT lite Insert YouTube videos in PowerPont slides with aS Desktop Copy embed code: (To copy code, click on the text box) Embed: URL: Thumbnail: WordPress Embed Customize Embed The presentation is successfully added In Your Favorites. Views: 1516 Category: Education License: All Rights Reserved Like it (4) Dislike it (0) Added: April 11, 2010 This Presentation is Public Favorites: 4 Presentation Description plz gv me ur i'd toooo Comments Posting comment... By: Fatzz (15 month(s) ago) can any1 plz mail me dis presetation.........plz.......... Saving..... Post Reply Close Saving..... Edit Comment Close By: meetujain (15 month(s) ago) asshokuim....... plz mail me ut correct id dear......... Saving..... Post Reply Close Saving..... Edit Comment Close By: asshokuim (15 month(s) ago) please send this ppt to my email id-asshokuim@gmail.com, I will be very thankful to u. Saving..... Post Reply Close Saving..... Edit Comment Close By: pintukumari (15 month(s) ago) ur slides are very very gud n i like them. so can u plz send me this ppt on my e mail id today itself i need them vey urgently .my id is gajbhiyepreeti4@gmail.com.thankz............ Saving..... Post Reply Close Saving..... Post Reply Close Saving..... Edit Comment Close By: meetujain (19 month(s) ago) gv me ur id yar.................. Saving..... Post Reply Close Saving..... Edit Comment Close loading.... See all Premium member Presentation Transcript Presentation oncryptography : Presentation oncryptography shaveta cryptography : cryptography Is a science of secret writing It’s a science and art of transforming messages to make them secure and immune to attacks Slide 3: sender receiver Intruder (unauthorized user) Plain text interrupts Slide 4: Plain text is original message After message is transformed it is called cipher text An encryption algorithm transfers plain text into cipher text using key A decryption algorithm transforms cipher text back into plain text using key. Cipher is defined as an encryption/decryption algorithm Key is number (set of number), that cipher as an algorithm operates on plain text Alice is a person who needs to send data Bob is receiver of data Eve is person who some how disturb the communication between Alice and bob Cryptography components : Cryptography components sender receiver Encryption (using encryption key) Decryption Using decryption key) Plain text Cipher text Plain text Are plain text, algorithms, cipher text Categories of cryptography : Categories of cryptography cryptography Symmetric-key Asymmetric-key Symmetric key cryptography is also called secret key Asymmetric key cryptography is also called public key Secret key Public key Keys and their types : Keys and their types Secret key is shared key used in symmetric-key cryptography Public key and private key are used in asymmetric-key cryptography Symmetric-key cryptography : Symmetric-key cryptography bob Alice encryption decryption Shared secret key Cipher text Here same key is used by sender for encryption and receiver (for decryption) The key is shared ( same key locks and unlocks box) Asymmetric-key cryptography : Asymmetric-key cryptography Alice bob encryption decryption Bobs Private key Bobs Public key It has 2 keys ;private and public ; alice uses public key to encrypt the message, private key is used by bob to decrypt message. Plain text Cipher text Plain text To the public Traditional ciphers : Traditional ciphers Traditional ciphers Substitution ciphers Transposition ciphers Mono alphabetic Poly alphabetic (are character oriented) Slide 11: Substitution cipher substitute one symbol with another for example it replaces a with d and t with z In mono alphabetic cipher a character in plain text is always changed to same character in cipher text for example in hello each and every time l is used it would be converted to d . Relation between character in plain text and cipher text is one to one relation In poly alphabetic cipher ,each occurrence of character can have different substitute one to many relation Substitution cipher and its types Slide 12: Shift cipher-:the simplest mono alphabetic cipher is shift cipher. in it encryption algorithm is ”shift key characters down” with key equal to number. the decryption algorithm is" shift key characters up” For example use shift cipher with key =15 to encrypt message hello Sol:- we encrypt one character at a time. each character is shifted 15 characters down. letter h is encrypted to w ;l to a ;e to t ;l to a ;l to a; O to d. cipher text is wtaad. Slide 13: Transposition cipher:-in it there is no substitution of characters ;instead their locations are changed Reorder (upward direction) Reorder (downward direction) Plain text (block) encryption Decryption Cipher text (block) Plain text (block) 1 2 3 4 1 2 3 4 (3142) Slide 14: X o r cipher:-it is made of set of simple ciphers .it uses exclusive-or-operation. input output An xor operation needs two data input First as plain text and second as key In other words one input is block to be encrypted ,other input is key Exclusive or X=a + b Or x=a’b+ ab’ Slide 15: Rotation cipher:-in it input bits are rotated to left or right. it can be keyed or keyless, in keyed rotation value of key defines number of rotation In keyless rotation number of rotation is fixed (special case of transposition cipher) 1 2 3 4 1 2 3 4 Substitution cipher (s-box):-the input to an s-box is stream of bits with length n ;the result is another stream of bits with length m .it is normally keyless sand is used in intermediate stage of encryption or decryption. A function that matches n input to m output N input bits M output bits Slide 16: Transposition cipher( p-box): it performs transposition at bit level ;it transposes bits .it can be implemented in software or hardware but hardware is faster .p-boxes are keyless there are three types of permutations in p-boxes In straight p-box there are same number of inputs as outputs In expansion p-box the number of output ports is greater than number of input ports Slide 17: In compression permutation cipher ,the number of output port is less than number of input ports Than comes modern round ciphers ;they involve multiple rounds ,where each round is complex cipher made of simple ciphers. the key used in each round is subset or variation of general key called round key if the cipher has n rounds the key generator produces and keys,k1,k2---kn Slide 18: Initial permutation Round 1 Round 2 Round 3 Final permutation round key generator K1 K2 K3 64 bit plain text 64 bit cipher text 64 bit key D E S Slide 19: 64 Bit plain text Encrypt D E S Decrypt D E S Encrypt D E S Decrypt D E S Encrypt D E S Decrypt D E S 64 Bit plain text 64 bit cipher text 64 bit plain text 64 bit cipher text Key 1 Key 2 Key 3 Key 1 key2 Key 3 Encryption triple D E S Decryption triple D E S TRIPLE D E S Slide 20: ROUND KEY GENERATOR ROUND1 ROUND 2 ROUND 10 + 128 BIT KEY K0 K1 128 BIT PLAIN TEXT 128 BIT CIPHER TEXT A E S K 2 K 10 Asymmetric-key cryptography : Asymmetric-key cryptography It has two keys :one private and one public In it two algorithms used are RSA and diffie-hellman RSA The most common public key algorithm is RSA , named for its inventors RIVEST,SHAMIR,ADLEMAN .It uses two numbers ,e and d ,as public and private key Selecting keys : Selecting keys Bob uses following steps to select the private and public keys Bob chooses two numbers p and q Bob multiplies above two prime numbers to get n (n=p*q) Bob calculates number =(p-1)*(q-1) Bob chooses random number e and calculates d so that d*e=1 mod phi Bob announces e and n to public He keep secret phi and d. RSA : RSA Alice C= pe mod n Calculating e ,d ,n bob p= cd mod n public e Plain text Cipher text encryption decryption Plain text private d Slide 24: encryption-:any one who needs to send message to bob can use n and e .for example if Alice needs to send message to bob, she can change message usually a short one ,to an integer. this is a plain text. she can then calculate cipher text ,using e and n. c=pe (mod n) Alice sends c, the cipher text to bob. Decryption-:bob keeps d as private. when he receives cipher text ;he uses his private key d to decrypt the message p=cd (mod n) Slide 25: example:-bob chooses p=7 and q=11 and calculates n=7*11=77 the value of phi =(7-1)*(11-1)=60.now he chooses two keys e ,d .e=13,d=37.now imagine alice sends plain text 5 to bob .she uses public key 13 to encrypt 5 Solution:-plaintext:5 c=pe (mod n)=513 (mod 77)=26 cipher text=26 Bob receives cipher text 26 and uses private keys 37 to decipher the cipher text. cipher text:26 P=cd (mod n) =2637(mod 77) Plain text=5 Slide 26: Diffie hellman was originally designed for key exchange. in diffie hell man crypto system ;two parties create a symmetric session key to exchange data without having to remember or store for future use. two parties needs to choose two numbers p and g . The first number p is a large prime number and second number is random number. p, g are public. Slide 27: Diffie hellman method Alice bob R1=gX mod p R2=gy mod p R1 R2 K=(R2)Xmod p K=(R1)Ymod p Shared secret key K=gxy mod p The value of p and g are public Slide 28: Step 1:l Alice chooses large random number x and calculates R1=gx mod p. Step 2:bob choses another large randon number y and calculates R2=gy mod p Step 3:alice sends R1 to bob (ALICE DOESNOT SENDS VALUE OF X;SHE ONLY SENDS R1) STEP 4:Bob sends R2 to Alice (BOB DOESNOT SENDS VALUE OF Y;HE SENDS ONLY R2) Step 5: Alice sends k=(R2)Xmod p. Step 6: bob also calculates k=(R1) Y mod p. The shared key in diffie hell man protocol is k=gxy mod p. Slide 29: Alice bob g g x y g g x y g y x g One third of key is public She sends key to bob He sends key to Alice The two keys are same because it does not matter if x is filled first or y Alice complete key by adding last part Bob complete key by adding last part Alice and bob fills up another one-third of secret key using her random number Slide 30: Alice Eve bob R1=gx mod p R1 R2=gz mod p R3=gy mod p R2 K1=(R2)Xmod p R2 K1=(R1)Z mod p K2=(R3)Z mod p K2=(R2)Y mod p R3 Alice- eve key Eve-bob key K1=gxz mod p K2=gzy mod p Man in middle attack Slide 31: The following happens 1. Alice chooses x calculates R1=gx mod p ,and sends R1to bob. 2. eve the intruder, intercepts R1.she chooses z ,calculates R2=gz mod p; and sends R2to both Alice and bob. bob chooses y, calculates R3=gy mod p ,and sends R3 to Alice;R3 is intercepted by eve and never reaches Alice. 4. Alice and eve calculate k1=gxz mod p, which becomes a shared key between Alice and eve .Alice, however, thinks that it is a key shared between bob and herself. 5. Eve and bob calculate k2=gzy mod p, which becomes a shared key between eve and bob. Bob, however ,thinks that it is a key shared between Alice and himself. It is also known as bucket bridge attack because it resembles a short line of volunteers passing a bucket of water from person to person Slide 32: THANKS Slide 33: ANY QUERIES