The spec. doesn't define behavior for the method
MessageDigestSpi.engineDigest(byte[] buff, int offset, int len)
when one of its parameters is illegal.

The spec says:
  "protected int engineDigest(byte[] buf, int offset, int len)
       throws DigestException

   Completes the hash computation by performing final operations such as
   padding. Once engineDigest has been called, the engine should be reset
   (see engineReset). Resetting is the responsibility of the engine implementor.
   This method should be abstract, but we leave it concrete for binary
   compatibility. Knowledgeable providers should override this method.

   Parameters:
       buf - the output buffer in which to store the digest
       offset - offset to start from in the output buffer
       len - number of bytes within buf allotted for the digest. Both this
         default implementation and the SUN provider do not return partial
         digests. The presence of this parameter is solely for consistency in
         our API's. If the value of this parameter is less than the actual
         digest length, the method will throw a DigestException. This parameter
         is ignored if its value is greater than or equal to the actual digest
         length.
  Returns:
       the length of the digest stored in the output buffer.
  Throws:
       DigestException - if an error occurs."

So, the behavior is defined only when len is illegal but the spec.
should also define the method behavior when:
1) 'buf' array is null
2) 'offset' is outside 'input' array bounds.

###@###.### 2004-02-26