code: func getSKIs(chain []*x509.Certificate, indices []int) (skis []string) {
  	for _, index := range indices {
  		ski := fmt.Sprintf("%X", chain[index].SubjectKeyId)
  		skis = append(skis, ski)
  	}
  	return
  }
docs: // getSKIs returns a list of cert subject key id  in the bundle chain with matched indices.