How does PGP handle multiple addresses?
When encrypting a message to multiple addresses, you will notice that the length of the encrypted file only increases by a small amount for each additional address. The reason that the message only grows by a small amount for each additional key is that the body of the message is only encrypted once using a random session key and IDEA. It is only necessary then to encrypt this session key once for each address and place it in the header of the message. Therefore, the total length of a message only increases by the size of a header segment for each additional address.
