4.1 RSA

The RSA-Cryptosystem calculates in Z_n , where n is the product of two primes. In the form presented here only numbers are encrypted. Texts must be coede aptly.
To send messages to Bob (cf. 4) encrypted with RSA the following steps have to be executed:

1.	Generate two large primes p und q ( p != q) (2.3.2)
2.	determine n = pq and phi(n) = ( p-1)(q-1)
3.	choose random b with 1 < b < phi(n) and gcd(b, phi(n)) = 1 (2.1)
4.	determine private key a = b-1 mod phi(n) (2.2)
5.	publish n and b as public keys

If Alice now wants to send a message m (< n) to Bob, she calculates x = m^b mod n (2.3.3).

Bob decodes the encrypted message x by calculating m = x^a mod n.


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5 DES