module OpenSSL::X509::Extension::SubjectKeyIdentifier

def subject_key_identifier

ASN1::ASN1Error.
Returns the binary String key identifier or nil or raises

exteension, as described in RFC5280 Section 4.2.1.2.
Get the subject's key identifier from the subjectKeyIdentifier 
def subject_key_identifier
  ext = find_extension("subjectKeyIdentifier")
  return nil if ext.nil?
  ski_asn1 = ASN1.decode(ext.value_der)
  if ext.critical? || ski_asn1.tag_class != :UNIVERSAL || ski_asn1.tag != ASN1::OCTET_STRING
    raise ASN1::ASN1Error, "invalid extension"
  end
  ski_asn1.value
end