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Unformatted text preview: Public Key Encryption Ratan Guha CIS 3360 Security in Computing Spring 2010 23 and 2810 Lecture 7 & 8 1 2 Resources Used Cryptography and Network Security, Fourth Edition, by William Stallings Lecture slides for the textbook by Lawrie Brown Lecture slides by Henric Johnson,Blekinge Institute of Technology, Sweden 3 Outline Outline Public Key Encryption Euler’s Totient Function φ ( n) RSA Public Key Encryption DiffieHellman Key Exchange Placement of En/Decryption Key Distribution PublicKey Cryptography probably most significant advance in the 3000 year history of cryptography uses two keys – a public & a private key asymmetric since parties are not equal uses clever application of number theoretic concepts to function complements rather than replaces private key crypto Why PublicKey Cryptography? developed to address two key issues: ❍ key distribution – how to have secure communications in general without having to trust a KDC with your key ❍ digital signatures – how to verify a message comes intact from the claimed sender public invention due to Whitfield Diffie & Martin Hellman at Stanford Uni in 1976 ❍ known earlier in classified community PublicKey Cryptography PublicKey Cryptosystems PublicKey Applications can classify uses into 3 categories: ❍ encryption/decryption (provide secrecy) ❍ digital signatures (provide authentication) ❍ key exchange (of session keys) some algorithms are suitable for all uses, others are specific to one Security of Public Key Schemes like private key schemes brute force exhaustive search attack is always theoretically possible but keys used are too large (>512bits) security relies on a large enough difference in difficulty between easy (en/decrypt) and hard (cryptanalyse) problems more generally the hard problem is known, but is made hard enough to be impractical to break requires the use of very large numbers hence is slow compared to private key schemes Euler’s Totient Function...
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 Spring '10
 Guha
 Cryptography, Euler, Alice K

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