I have some comments on sec 4.2.1.2 of the rfc 2459. It says to facilitate chain building, the subject key identifier extenion must appear in all conforming CA certificates. In fact, it is not always true. If the CA issuers the certificates, and use the authorityCertIssuer + authorityCertIssuerSerialNumber as these cetificates' authority key identifier extenion, then the CA certificte need not include the subject key identifier, because the information is included in its basic certificate fields. I think the subject key identifier must be included in CA certificate only if the CA issuers the certificates, and use keyIdentifier as these cetificates' authority key identifier extenion. Regards Wei-Ching Su Senior Engineer FISC (Financial Information Service Co., LTD.) Taipei, Taiwan