I have a fair idea of what RSA encryption is and how to do it, but I don't quite understand the following bit given in my textbook:
I have an exam tomorrow and I'm expected to encrypt a string of text (e.g., "meet me tomorrow.") using RSA encryption. If somebody could clarify what that bit means, I'll be good to go.
We divide the string into equal parts of size $2N$. Each "block" gives us an integer $M_i$. We encrypt each block using the function given. Then we concatenate all the encrypted blocks. The restriction that $2525...25$ should be less than $n$ is there so that each different block gives a unique integer modulo $n$. Otherwise say if $n = 11*13 = 143$ and we pick a block size of $4$ (that is $2N = 4$) then $1001$('kb') and $0000$('aa') both would be $0$ modulo $143$ and you couldn't tell whether $0$ means 'kb' or 'aa'. In this case we should pick a block size of $2$ so the largest integer we could get $25$('z') is less than $143$