# why RSA uses Semiprime numbers? [duplicate]

Why does RSA use semiprime numbers? Why not just use any big number ??
What is the advantage of the two original numbers being prime?

Because factoring any big number will be difficult

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## marked as duplicate by Henrick Hellström, figlesquidge, DrLecter, orlp, e-sushi Dec 7 '13 at 11:49

@user16...: Example: Try and factor $2^{1337}$. That's a very big number, but its definitely not hard to factor! –  figlesquidge Dec 7 '13 at 10:31