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Edit Comment Close Premium member Presentation Transcript CRYPTOGRAPHY : CRYPTOGRAPHY Presented By:- Sonam Runkani 73017 Dushyant Joshi 73018 Prashant Tripathy 73019 Niraj Singh 73020 Cryptography : Cryptography Defn: Art of achieving security by encoding messages. Cryptography is associated with scrambling plaintext into ciphertext, then back again. Plain and Cipher Texts : Plain and Cipher Texts Plaintext Signifies a message that could be understood by everyone. Ciphertext Encoded plain text message. Plain text Message being transformed into Cipher text : Plain text Message being transformed into Cipher text PLAIN TEXT MESSAGE CORRESPONDING CIPHER TEXT MESSAGE Two ways of codifying the Plain Text : Two ways of codifying the Plain Text Substitution Technique Replacement of one alphabet with another Transposition Technique Performs permutation over the plain text along with replacement of one alphabet with another SUBSTITUTION TECHNIQUE : SUBSTITUTION TECHNIQUE 1) Ceasar Cipher Characters of plain text message are replaced by other characters three places down the line. Plain Text Cipher Text SUBSTITUTION TECHNIQUE Contd.. : 2)Modified Version of Ceaser Cipher Messages could be replaced by any characters down the line, instead of three place down the line. E.g.: Plain Text Hello Cipher Text Error SUBSTITUTION TECHNIQUE Contd.. SUBSTITUTION TECHNIQUE Contd.. : 3)Mono-Alphabetic Cipher Message could be replaced with any permutation or combination of 26 alphabets. Possibilities: 26*25*24….*2 or 4*1026 SUBSTITUTION TECHNIQUE Contd.. TRANSPOSITION TECHNIQUE : 1)Rail Fence Technique Involves writing plain text as a sequence of diagonals and then reading it row-by-row to produce cipher text T A S O I I N R N P S T O Plain Text TRANSPOSITION Cipher Text TASOIINRNPSTO TRANSPOSITION TECHNIQUE TRANSPOSITION TECHNIQUE Contd.. : TRANSPOSITION TECHNIQUE Contd.. 2)Simple Columnar Technique Simply arranges the plain text as a sequence of rows of a rectangle that are read in columns. Plain Text:TRANSPOSITION Random Order:4,6,1,2,5,3 Cipher Text:NTPOTONRSSIAI Encryption : Encryption Process of encoding plain text message into cipher text message Decryption HELLO KHOOR Plain Text Cipher Text Encrypt Process of decoding cipher text message back into plain text message HELLO KHOOR Plain Text Cipher Text Decrypt Encryption & Decryption In Real World : Encryption & Decryption In Real World Hello Ifmmp Ifmmp Hello Internet Encrypt Decrypt Plain Text Plain Text Cipher Text Cipher Text Sender Receiver Types Of Cryptosystem : Types Of Cryptosystem Symmetric Cryptosystem Makes use of single secret key to encrypt the data. Asymmetric Cryptosystem Built around possession of a pair of keys: a Public key and a Private key Symmetric Cryptosystems : Symmetric Cryptosystems Block Cipher Mode: Data to be encrypted is broken into fixed size of blocks Amar Encrypt Encrypt Encrypt Akbar Anthony *hds$ Vfa# dfg#tyt Plain Text Cipher Text The encryption process at the sender’s end Contd….. : Contd….. Decrypt Decrypt Decrypt Akbar Anthony *hds$ Vfa# dfg#tyt Amar Cipher Text Plain Text The decryption process at the receiver’s end Slide 16: Stream Cipher: In Stream Cipher the plain text is encrypted one bit at a time by applying the XOR logic as the encryption algorithm Symmetric Cryptosystems Contd Asymmetric Algorithm : Asymmetric Algorithm Confidentiality Encryption Decryption Msg Cipher Text Msg Sender A (PKA,SKA) Receiver B (PKB,SKB) PKB SKB Contd….. : Contd….. Authentication Signing Verification Msg Msg Signature SKA PKA Signature Valid? Sender A (PKA,SKA) Receiver B (PKB,SKB) What makes encryption algorithm secure? : What makes encryption algorithm secure? Use of strong and powerful keys Generating a new key for sending a new fresh document DIFFIE HELLMAN KEY EXCHANGE PROTOCOL : DIFFIE HELLMAN KEY EXCHANGE PROTOCOL Also called as “Exponential Key Agreement” developed in 1976. Not an encryption method but cryptographic key exchange method. Allows exchange of secret keys over insecure medium. WORKING OF DIFFIE HELLMAN : WORKING OF DIFFIE HELLMAN Users agree on two large prime numbers say n and g. First user chooses random number x, thus calculating A from it by using A= gx mod n. Second user chooses random number y, and calculates B as B= gy mod n. Secret key for first user is computed as k1=Bxmod n. Secret key k2=Ay mod n. Finally we get K1=K2 Example : Example Let n=11 , g=7 (Prime Numbers) Let x=3 , y=6 (Random Numbers) Calculating: A=gx mod n =73 mod 11 =343 mod 11 =2 B=gy mod n =76 mod 11 =117649 mod 11 =4 Example Contd.. : Example Contd.. Generating secret key K1=Bx mod n =43 mod 11 = 64 mod 11 = 9 K2=Ay mod n =26 mod 11 =64 mod 11 =9 Thus K1=K2 Problem with the algorithm : Problem with the algorithm Vulnerable to Man-in-the-Middle attack Man in the Middle may establish two distinct Diffie-Hellman keys between the sender and receiver and then try to masquerade sender to receiver and vice-versa Properties of Trustworthy Encryption System : Properties of Trustworthy Encryption System Key length is kept relatively large Use of best possible encryption algorithm Use of Public Key Encryption rather than Symmetric Key Encryption Proper implementation of authentication mechanism to check for the source of data. Digital Signatures : Digital Signatures Used for: Authenticity of message Verifying message Integrity. But how ? Working of Digital Signatures : Working of Digital Signatures Message is encrypted with sender’s private key generating ‘Signature’. Message+Signature send to the destination. Message decrypted using sender’s public key. Comparison of result and copy of received message. HASH FUNCTIONS : HASH FUNCTIONS Digitally signing messages creates large overheads. Hash function reduces these overheads. These generate messages of fixed but of much smaller length called as Message Digests Changes in original message causes message digest to change. Digital Signature Verification : Digital Signature Verification Slide 30: Questions ? You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.
Cyptography dev007 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: 397 Category: Education License: All Rights Reserved Like it (0) Dislike it (0) Added: August 29, 2008 This Presentation is Public Favorites: 0 Presentation Description ppt Comments Posting comment... By: shiva_eluru (43 month(s) ago) I want to see ur presentation. i am unable to access your presentation. Saving..... Post Reply Close Saving..... Edit Comment Close Premium member Presentation Transcript CRYPTOGRAPHY : CRYPTOGRAPHY Presented By:- Sonam Runkani 73017 Dushyant Joshi 73018 Prashant Tripathy 73019 Niraj Singh 73020 Cryptography : Cryptography Defn: Art of achieving security by encoding messages. Cryptography is associated with scrambling plaintext into ciphertext, then back again. Plain and Cipher Texts : Plain and Cipher Texts Plaintext Signifies a message that could be understood by everyone. Ciphertext Encoded plain text message. Plain text Message being transformed into Cipher text : Plain text Message being transformed into Cipher text PLAIN TEXT MESSAGE CORRESPONDING CIPHER TEXT MESSAGE Two ways of codifying the Plain Text : Two ways of codifying the Plain Text Substitution Technique Replacement of one alphabet with another Transposition Technique Performs permutation over the plain text along with replacement of one alphabet with another SUBSTITUTION TECHNIQUE : SUBSTITUTION TECHNIQUE 1) Ceasar Cipher Characters of plain text message are replaced by other characters three places down the line. Plain Text Cipher Text SUBSTITUTION TECHNIQUE Contd.. : 2)Modified Version of Ceaser Cipher Messages could be replaced by any characters down the line, instead of three place down the line. E.g.: Plain Text Hello Cipher Text Error SUBSTITUTION TECHNIQUE Contd.. SUBSTITUTION TECHNIQUE Contd.. : 3)Mono-Alphabetic Cipher Message could be replaced with any permutation or combination of 26 alphabets. Possibilities: 26*25*24….*2 or 4*1026 SUBSTITUTION TECHNIQUE Contd.. TRANSPOSITION TECHNIQUE : 1)Rail Fence Technique Involves writing plain text as a sequence of diagonals and then reading it row-by-row to produce cipher text T A S O I I N R N P S T O Plain Text TRANSPOSITION Cipher Text TASOIINRNPSTO TRANSPOSITION TECHNIQUE TRANSPOSITION TECHNIQUE Contd.. : TRANSPOSITION TECHNIQUE Contd.. 2)Simple Columnar Technique Simply arranges the plain text as a sequence of rows of a rectangle that are read in columns. Plain Text:TRANSPOSITION Random Order:4,6,1,2,5,3 Cipher Text:NTPOTONRSSIAI Encryption : Encryption Process of encoding plain text message into cipher text message Decryption HELLO KHOOR Plain Text Cipher Text Encrypt Process of decoding cipher text message back into plain text message HELLO KHOOR Plain Text Cipher Text Decrypt Encryption & Decryption In Real World : Encryption & Decryption In Real World Hello Ifmmp Ifmmp Hello Internet Encrypt Decrypt Plain Text Plain Text Cipher Text Cipher Text Sender Receiver Types Of Cryptosystem : Types Of Cryptosystem Symmetric Cryptosystem Makes use of single secret key to encrypt the data. Asymmetric Cryptosystem Built around possession of a pair of keys: a Public key and a Private key Symmetric Cryptosystems : Symmetric Cryptosystems Block Cipher Mode: Data to be encrypted is broken into fixed size of blocks Amar Encrypt Encrypt Encrypt Akbar Anthony *hds$ Vfa# dfg#tyt Plain Text Cipher Text The encryption process at the sender’s end Contd….. : Contd….. Decrypt Decrypt Decrypt Akbar Anthony *hds$ Vfa# dfg#tyt Amar Cipher Text Plain Text The decryption process at the receiver’s end Slide 16: Stream Cipher: In Stream Cipher the plain text is encrypted one bit at a time by applying the XOR logic as the encryption algorithm Symmetric Cryptosystems Contd Asymmetric Algorithm : Asymmetric Algorithm Confidentiality Encryption Decryption Msg Cipher Text Msg Sender A (PKA,SKA) Receiver B (PKB,SKB) PKB SKB Contd….. : Contd….. Authentication Signing Verification Msg Msg Signature SKA PKA Signature Valid? Sender A (PKA,SKA) Receiver B (PKB,SKB) What makes encryption algorithm secure? : What makes encryption algorithm secure? Use of strong and powerful keys Generating a new key for sending a new fresh document DIFFIE HELLMAN KEY EXCHANGE PROTOCOL : DIFFIE HELLMAN KEY EXCHANGE PROTOCOL Also called as “Exponential Key Agreement” developed in 1976. Not an encryption method but cryptographic key exchange method. Allows exchange of secret keys over insecure medium. WORKING OF DIFFIE HELLMAN : WORKING OF DIFFIE HELLMAN Users agree on two large prime numbers say n and g. First user chooses random number x, thus calculating A from it by using A= gx mod n. Second user chooses random number y, and calculates B as B= gy mod n. Secret key for first user is computed as k1=Bxmod n. Secret key k2=Ay mod n. Finally we get K1=K2 Example : Example Let n=11 , g=7 (Prime Numbers) Let x=3 , y=6 (Random Numbers) Calculating: A=gx mod n =73 mod 11 =343 mod 11 =2 B=gy mod n =76 mod 11 =117649 mod 11 =4 Example Contd.. : Example Contd.. Generating secret key K1=Bx mod n =43 mod 11 = 64 mod 11 = 9 K2=Ay mod n =26 mod 11 =64 mod 11 =9 Thus K1=K2 Problem with the algorithm : Problem with the algorithm Vulnerable to Man-in-the-Middle attack Man in the Middle may establish two distinct Diffie-Hellman keys between the sender and receiver and then try to masquerade sender to receiver and vice-versa Properties of Trustworthy Encryption System : Properties of Trustworthy Encryption System Key length is kept relatively large Use of best possible encryption algorithm Use of Public Key Encryption rather than Symmetric Key Encryption Proper implementation of authentication mechanism to check for the source of data. Digital Signatures : Digital Signatures Used for: Authenticity of message Verifying message Integrity. But how ? Working of Digital Signatures : Working of Digital Signatures Message is encrypted with sender’s private key generating ‘Signature’. Message+Signature send to the destination. Message decrypted using sender’s public key. Comparison of result and copy of received message. HASH FUNCTIONS : HASH FUNCTIONS Digitally signing messages creates large overheads. Hash function reduces these overheads. These generate messages of fixed but of much smaller length called as Message Digests Changes in original message causes message digest to change. Digital Signature Verification : Digital Signature Verification Slide 30: Questions ?