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Lecture 6 - C lass Note Public Key Encryption Need...

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Class Note September 25, 2008 Public Key Encryption Need alternative to the symmetric key encryption - Key exchange is only possible after secure communication has been established - Number of keys needed is quadratic in the number of users Now asymmetric encryption is used instead - Use two keys - One is kept private, one is public - Reduces the number of keys needed Now the number of keys is 2*n users rather than n 2 Secret/Symmetric vs Public/Assymetric Two users one key two keys Prot. Of keys kept secret at all times one public, one private Key dist. Key exchange must Can use the public key Be done “out of Band” Speed Very fast (relative) Slow (10,000 times slower) RSA-
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Secure to this day; developed in 1978; based on a very simple principle: it is easy to multiply two numbers, but is very hard to factor a large number. On a computer, factoring a really large number (give all the divisors of a really large number). These are called one way functions. Two generate an RSA crypto system we first need to very large prime numbers (P and Q). These numbers are multiplied to give us the modulus (n) which has 512 bits or more.
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