Symmetric encryption is much faster than asymmetric encryption, but it has several problems. First, both parties (sender and receiver) need to know the shared secret key. This means that the two parties need to have some method for securely exchanging the key. E-mail is not a solution, because anyone who can intercept the e-mail would know the secret key. A second problem is that separate secret keys need to be created for use with each different party with whom encryption is going to be used. Otherwise, anyone possessing that common secret key could decrypt any encrypted documents to which access is obtained, legitimately or illegitimately, whether intended for that person or not. The number of secret keys required grows quickly, becoming difficult to manage if encryption is desired with thousands of other entities. Third, because both parties using symmetric encryption must know the same secret key, there is no way to prove who created a specific document. Each party could claim that other used the shared secret key in an attempt to defraud. Thus, symmetric encryption provides no way to create legally binding agreements.