Read the excerpt from The Code Book . Alternatively, imagine that a bank receives an e-mail from a client, which instructs that all the client's funds should be transferred to a private numbered bank account in the Cayman Islands. Once again, without a handwritten signature, how does the bank know that the e-mail is really from the client? The e-mail could have been written by a criminal attempting to divert the money to his own Cayman Islands bank account. In order to develop trust on the Internet, it is essential that there is some form of reliable digital signature. How does the author support the claim that "it is essential that there is some form of reliable digital signature”?