[1] [CITE@en[RFC 5280 - Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile]]
([TIME[2018-07-29 16:13:13 +09:00]])
<https://tools.ietf.org/html/rfc5280#section-4.2.1.2>

[2] [CITE[Certificate Error: How to validate the Subject Key Identifier (SKI) from a X509 certificate]]
([TIME[2018-05-28 10:06:09 +09:00]])
<http://certificateerror.blogspot.com/2011/02/how-to-validate-subject-key-identifier.html>

[3] 
[[basic constraints]] の [CODE[cA]] が[[真]]なら、[MUST[必須]]です。

[4] 
[[EE証明書]]でも指定できます。

[5] 
[[AKI]] も参照。