How to generate public key and private key XML string u

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C#

hello,
i want to generate the public key and private key by passing our own string.

Suppose my string is "hello how are you" and i want to generate the public and private key for this string.

What I have tried:

RSACryptoServiceProvider rsa;
           const int PROVIDER_RSA_FULL = 1;
           const string CONTAINER_NAME = "test";
           CspParameters cspParams;
           cspParams = new CspParameters(PROVIDER_RSA_FULL);
           cspParams.KeyContainerName = CONTAINER_NAME;
           cspParams.Flags = CspProviderFlags.UseMachineKeyStore;

           rsa = new RSACryptoServiceProvider(cspParams);
           string publicPrivateKeyXML = rsa.ToXmlString(true);
           string publicOnlyKeyXML = rsa.ToXmlString(false);

here i am using this code by copied it from one site. here i am confuse in can we pass our own string to get public key and private key.