This interface represents a encryption template, which is the same as the
* desired xml encryption element[ EncryptedType ] but some of the nodes may be
* empty. The empty entities include CipherValue, which is a subset of
* EncryptedData or EncryptedKey. Empty entities are not allowed in a encryption
* template when performing decryption.
*
*
In some cases, the encrypter or decrypter can dertermine and locate the
* EncrytedKey from the encryption template by dereference the RetrievalMethod
* inside EncryptedData.
*
*
In some cases, the EncryptedKey need to be clearly pointed out by the
* encryption template.
*
*
With the help of encryption context, the encrypter or decrypter specifies
* the key from the KeyInfo in the encryption template.
*
*
*
It isn't a good method to set the EncryptedKey here. In general, there is
* a RetrievalMethod in EncryptedData by which we can get the EncryptedKey.
*
* And some times, in the low level, it is hard to determine what the key is
* except that the high level application tell the mechanism and parameters.
*
* So I think it will be more simple that the application set the encrypted key
* information. In this case, the application only need to know the xml schema
* or DTD and the encryption device. If so, the high level application takes the
* action of build the EncryptedKey template and references it in the element of
* EncryptedData. And in this case, the calling to set up EncryptedKey template
* and target is not necessary, because the encrypter or decrypter can determine
* and locate the EncrypedKet from the encryption template of EncryptedData by
* dereference the RetrievalMethod.
*
* In some situation, the high level applications do not want to know anything
* about crypto devices( May be he must, because the lower level do not know
* what the key is ). If it gives the key value, it can get EncryptedKey by
* setting the key template and key value target.
