csce522-lect6-fenner

csce522-lect6-fenner - Public Key Encryption Terminology...

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Public Key Encryption Terminology RSA Security Protocols CSCE 522 - Farkas
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CSCE 522 - Farkas 2 Lecture 6 Reading Assignment Reading assignments for current lecture: Required: Pfleeger: 2.7, …, 2.12 Recommended : C. Meadows: Formal Methods for Cryptographic Protocol Analysis: Emerging Issues and Trends, http://citeseer.ist.psu.edu/meadows03formal.html CSCE 522 - Farkas
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Summary of Secret Key Encryption Basic methods: Substitution Transposition Security: secrecy of secret key CSCE 522 - Farkas
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Compare DES and AES DES AES Date 1976 1999 Block size 64 bits 128 bits Key length 56 bits 128, 192, 256 bits Encryption Substitution, permutation Substitution, shift, mixing Cryptography Confusion, diffusion Confusion, diffusion Design Open Open Design rationale Closed Open Selection process Secret Secret with public comments Source IBM, enhanced by NSA Independent Dutch cryptographers CSCE 522 - Farkas
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Weakness of Secret Key Encryption Secrecy of key How to distribute the keys securely? Large number of keys N(N-1) / 2 Other issues: no support for Third party verification Non-repudiation CSCE 522 - Farkas Can we provide other methods for confidentiality?
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CSCE 522 - Farkas 6 Public-Key Encryption Two keys – one is private one is public Solves the key distribution problem (but need reliable channel) Provides electronic signatures Slower than secret-key encryption
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CSCE 522 - Farkas 7 Public-Key Encryption Needed for security : One of the keys must be kept secret Impossible (at least impractical) to decipher message if no other information is available Knowledge of algorithm, one of the keys, and samples of ciphertext must be insufficient to determine the other key
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CSCE 522 - Farkas 8 Confidentiality A Sender B Recipient Insecure channel Plaintext Plaintext Ciphertext Encryption Alg. Decryption Alg. B’s public key B’s private key (need reliable channel)
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CSCE 522 - Farkas 9 Public Key Cryptosystem Concept conceived by Diffie and Hellman in 1976 Rivest, Shamir, and Adleman (RSA) describe a public key system in 1978 Many proposals have been broken e.g., Merkle-Hellman proposal broken by Shamir Serious candidates (public domain) RSA El Gamal
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RSA CSCE 522 - Farkas
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CSCE 522 - Farkas 11 Notation C = E(KE-B, M) M = D(KD-B,C) KE-B: public key of B KD-B: private key of B E: encryption alg. D: decryption alg. M: plaintext C: ciphertext
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CSCE 522 - Farkas 12 RSA Both sender and receiver know n Sender knows e Only receiver knows d Modulus: Remainder after division, i.e., i f a mod n=b then a=c*n+b Need: Find values e,d,n such that Easy to calculate M e , C d for all M < n Infeasible to determine d give e M ed mod n = M mod n
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CSCE 522 - Farkas 13 RSA Public key: (n,e) Secret key: (n,d) n is a 200 digit number C = M e mod n M = C d mod n
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14 RSA Keys
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csce522-lect6-fenner - Public Key Encryption Terminology...

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