How encryption works in RSA cryptosystem
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I understand how RSA cryptosystem works but what i don't understand is that in the algorithm http://en.wikipedia.org/wiki/RSA_%28algorithm%29 we send encrypted message to another person. Normally we write string as meesage. I want to know how this string is converted to a number. I see everywhere on internet people mentioned this message as numbers in all examples. But we don't send numbers normally, we send string as message. I want to know how this string is converted in numbers. I mean i know how to convert a string in number but in cryptographic view how this message is converted to numbers? 