def key_fingerprint(type = OpenSSL::Digest::SHA1)
      type.new(@spki.value.last.value)
    end
def key_fingerprint(type = OpenSSL::Digest::SHA1)
      type.new(@spki.value.last.value)
    end
Return a digest object for the *public key* data.

 Some specifications (such as RFC5280's subjectKeyId) want a fingerprint
 of only the key data, rather than a fingerprint of the entire SPKI
 structure.  If so, this is the method for you.

 Because different things want their fingerprints in different formats,
 this method returns a *digest object*, rather than a string, on which
 you can call whatever output format method you like (`#digest`, `#hexdigest`,
 or `#base64digest`, as appropriate).

 @param type [OpenSSL::Digest] override the default hash function used
   to calculate the digest.  The default, SHA1, is in line with the most
   common use of the key fingerprint, which is RFC5280 subjectKeyId
   calculation, however if you wish to use a different hash function
   you can pass an alternate digest class to use.

 @return [OpenSSL::Digest]