Interface for cryptographic hash functions.

The add method is used to add data to the hash. The close method is used to extract the message digest.

Once the close method has been called no more data can be added using the add method. If add is called after the first call to close a HashException is thrown.

If multiple instances of a given Hash is needed the newInstance method can provide a new instance.

abstract class Hash {
 /**
  * Add a list of bytes to the hash computation.
  */
 add(List<int> data);

 /**
  * Finish the hash computation and extract the message digest as
  * a list of bytes.
  */
 List<int> close();

 /**
  * Returns a new instance of this hash function.
  */
 Hash newInstance();

 /**
  * Internal block size of the hash in bytes.
  *
  * This is exposed for use by the HMAC class which needs to know the
  * block size for the [Hash] it is using.
  */
 int get blockSize;
}