can we generate public and private keys manually??of rsa encryption

yes fine sachin... but an attacker can apply this rsacryptoprovider and encrypt and decrypt files so is there any way of creating security such as key pair generation manually to avoid such attacks??

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

Please do the needful help 

An algorithm means set of steps , if you can manually follow those steps then you can , encryption on the other hand means converts something into bytes with the help of random entity, in case of rsa the keys are randomly generated when you use default RSACryptoServiceProvider , and this is all abou RSA , manually generating keys doesn't make sense.

 manually generating keys means applying your own algorithm.