1.Alice knows the message must be from Bob because no one else has the SK needed to produce the valid signature.
由于没有其他人知道产生合法签名所需的密钥，爱丽丝便能确定讯息是来自鲍伯。
2.Select one or more issuance policies. A valid signature can contain any one of the issuance policies you select.
选择一个或多个发布策略。有效的签字可包含您选择的任何一个发布策略。