数字签名 Alice Bob sign verify SA =SA(M') PA >accept M (M',o) M' communication channel Figure 31.6 Digital signatures in a public-key system.Alice signs the message M'by appending her digital signature o =SA(M)to it.She transmits the message/signature pair(M',o)to Bob, who verifies it by checking the equation M'=P().If the equation holds,he accepts (M'.o)as a message that Alice has signed.数字签名