 Factorization is possibly an example of so-called trapdoor one-to-one function which is easy to compute from one side but very difficult in its inverse. Whether factorization is really difficult, remains an open question, although most mathematicians believe the problem to be hard. Note that factorization in this context can be seen as the process of decoding a message. If factorization is hard it can be used as an encryption technique. Classical encryption techniques, like RSA, are based on multiplying codes with large prime numbers. Suppose Alice has a message encoded as a large number m and she knows Bob has access to a large prime p. She sends the number \(p \times m = n\) to Bob. Since Bob knows p he can easily reconstruct m by computing \(m = n/p\). Since factorization is difficult any other person that receives the message n will have a hard time reconstructing m.