Methods, systems and security devices for rendering digital invisible ink, can involve representing an invisible item in a single color that is not discernable from white by a human eye, embedding the invisible item into white space of a digital document, and converting the invisible item into a visible item using a transform table that defines how to convert the single color of the invisible item so that the invisible item after a conversion to the visible item is discernable by the human eye.

The disclosure relates to message encoding. One claim recites an apparatus comprising: an input to receive a message key for transforming a plural-bit message, the message key having been generated through transforming a multi-bit seed with a randomizing process, and encoding the transformed multi-bit seed with error correction encoding, the transforming and encoding yielding the message key; electronic memory for storing a plural-bit message; and an electronic processor programmed for transforming the plural-bit message with the message key to yield a transformed message, and programmed as an encoder for encoding the transformed message key in data representing audio or imagery, thereby transforming the data representing audio or imagery. Of course, other claims and combinations are provided too.