１．数字证书的颁发用户要在网上交易或与其他用户交换信息，必须证明自己的身份。证明身份最好的方法是数字证书。而证书的颁发工作必须由能得到普遍信任的权威机构来担任。由于网络用户之间可能相距万里，不可能面对面交换公开密钥，必须找一家大家都信任的机构，来证明每位 1. Issuing Digital Certificates Users must prove their identity by trading online or exchanging information with other users. The best way to prove your identity is digital certificates. The issuance of certificates must be made by an authority that can be universally trusted. As network users may be thousands of miles apart, it is impossible to face-to-face exchange of public keys, we must find a trusted agency we all have to prove that each