ASN1.decode(der)DER表現の文字列を解析し、OpenSSL::ASN1::ASN1Data(のサブクラス)のインスタンスを返す。
ruby -e '
require "openssl"
require "pp"
pem = File.read(ARGV[0])
cert = OpenSSL::X509::Certificate.new(pem)
pp OpenSSL::ASN1.decode(cert.to_der)
' mycert.pem
#<OpenSSL::ASN1::Sequence:0x814e9fc
@tag=16,
@tag_class=:UNIVERSAL,
@tagging=nil,
@value=
[#<OpenSSL::ASN1::Sequence:0x814ead8
@tag=16,
@tag_class=:UNIVERSAL,
@tagging=nil,
@value=
[#<OpenSSL::ASN1::ASN1Data:0x814f690
@tag=0,
@tag_class=:CONTEXT_SPECIFIC,
@value=
[#<OpenSSL::ASN1::Integer:0x814f6a4
@tag=2,
@tag_class=:UNIVERSAL,
@tagging=nil,
@value=2>]>,
...