Cryptography in Dot Net

I need the cryptography code.. where it maintain the seperate perate and public key for encryption and decryption.
I have tried RSA algorithm...
let me get any sample code for above cryptography or any other.
The public and private key are given by me as a string.
i.e publicKey = "mypublicKey12"
     privateKey = "myprivateKey12"
 
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