code: public final ProtocolDataUnit create (final String headerDigest, final String dataDigest) {
  
          return new ProtocolDataUnit(digestFactory.create(headerDigest), digestFactory.create(dataDigest));
      }
docs: This method creates a <code>ProtocolDataUnit</code> instance, which initializes only the digests to use, and
  returns it.
  
  @param headerDigest The name of the digest to use for the protection of the Basic Header Segment.
  @param dataDigest The name of the digest to use for the protection of the Data Segment.
  @return A new <code>ProtocolDataUnit</code> instance.