4[4]S Kent.Privacy Enhancement for Internet Electronic Mail:Part 2: Certificate_Based Key Management.RFC 1422,1993.2
5[5]Internet Public Key Infrastructure-X.509 Certificate and CRL Profile.Section 6:PKIX Working Group Internet Draft
6[6]M Myers,R Ankey,A Malpani,et al.X.509 Internet Public Key Infrastructure Online Certificate Status Protocol-OCSP.IETF X.509 PKIX Working Group,1998.9(draft)
7[7]R Housley,W Ford,W Polk,et al.Internet X.509 Public Key Infrastrocture Certificate and CRL Profile.RFC 2459,1999.1