メモメモ x509/pem

http://golang.org/pkg/crypto/x509/#example_Certificate_Verify

https://ja.wikipedia.org/wiki/X.509#.E8.A8.BC.E6.98.8E.E6.9B.B8.E3.83.95.E3.82.A1.E3.82.A4.E3.83.AB.E3.81.AE.E6.8B.A1.E5.BC.B5.E5.AD.90

https://en.wikipedia.org/wiki/Privacy-enhanced_Electronic_Mail

Abstract Syntax Notation One - Wikipedia

https://en.wikipedia.org/wiki/X.690#DER_encoding

https://en.wikipedia.org/wiki/X.690#BER_encoding