iaik.asn1
Interface EncodeListener

All Superinterfaces:

EventListener

All Known Implementing Classes:

SignerInfo, DigestedDataStream

public interface EncodeListener

extends EventListener

Interface to be implemented for supplying relevant information actually during the encoding process. Implementing this interface may be useful in situations, where data to be encoded is not known before the encoding actually is performed. Imaging, for instance, some structure that shall be encoded as an ASN.1 SEQUENCE object having an OCTET_STRING as one of its components. Imagine furthermore, that the byte value supplying the contents of the OCTET_STRING component is not known at beginning of the encoding procedure. When writing the toASN1Object method of such a structure, use an empty OCTET_STRING for the not-yet known byte value, and implement the encodeCalled method to set the OCTET_STRING value actually during the encoding is performed, e.g.:

 class xxx implements EncodeListener {
   ...
   byte[] value;
   ...

   public ASN1Object toASN1Object() throws CodingException {
      SEQUENCE seq = new SEQUENCE();
      ...
      // create an empty octet string and register as encode listener
     OCTET_STRING oct = OCTET_STRING();
     oct.addEncodeListener(this, 1);
   }

   ...

   // implement the encodeCalled method for setting the value during the
   // encoding actually is performed
   public void encodeCalled(ASN1Object o, int id) throws CodingException {
      ...
      o.setValue(value);
   }
   ...
 }
 

Now, when calling DerCoder.encode(xxx.toASN1Object()) for performing the DER encoding, the addEncodeListener method of the ASN1Object class is used for registering the calling instance of the xxx class to be notified when the OCTET_STRING component actually has to be encoded. Later, the programm execution will jump to the encodeCalled method of the xxx instance for obtaining the OCTET_STRING value. The encode method of the OCTET_STRING instance itself will be executed not before the encodeCalled methods of all registeres listeners have been executed.

Within the IAIK-JCE library, the EncodeListener utility is used for the stream implementations of the several PKCS#7 content types, where the raw data to be processed - e.g. signed for the example of the SignedData type - is supplied from an input stream that is not read before the encoding actually is performed. Since the, for instance, encryptedDigest value of an inherent SigenrInfo depends on the data supplied from the stream, it cannot be calculated before the stream has been read, and therefore has been set during the encoding. For that reason, the SignerInfo class implemets the EncodeListener interface.

Version:

File Revision 15

See Also:

ASN1Object

Method Summary

void	encodeCalled(ASN1Object o, int id) Method to be implemented for being called during the encoding procedure.

Method Detail

encodeCalled

public void encodeCalled(ASN1Object o,
                         int id)
                  throws CodingException

Method to be implemented for being called during the encoding procedure.

Use this method for setting specific properties of the supplied ASN1Object actually during the encoding is performed. If the EncodeListener wishes to be notified about the encoding process of more than only one object, use different id values to distinguish between the several objects.

Parameters:

o - the ASN1Object to be supplied with information during the encoding process

id - an id that may be used to listen for more than only one object encodings

Throws:

CodingException - if an error occurs during the encoding procedure