6. There are several reasons why it is good practice to separate RSA digtal signature key pairs and RSA encryption key pairs. (a) If Alice is using the same RSA key pair for both digital signatures and encryption, explain how Bob could forge Alice's signature on a message of his choice if Alice is 'foolish' enough to help him. (b) Why is this a more powerful attack than the existential forgery that we described in Section 7.3.4? (c) What other reasons are there for keeping these key pairs separate