13. An apparatus comprising: electronic memory for storing data representing at least a portion of a text document; an electronic processor programmed for: forming a message; spreading the message over a carrier signal to yield a spread spectrum message; modifying distances of existing spaces between words to encode a machine-detectable interword modification in the document based on elements of the spread spectrum message, in which interword modifications are controlled to form a machine-detectable message in the text document.
13. An apparatus comprising: electronic memory for storing data representing at least a portion of a text document; an electronic processor programmed for: forming a message; spreading the message over a carrier signal to yield a spread spectrum message; modifying distances of existing spaces between words to encode a machine-detectable interword modification in the document based on elements of the spread spectrum message, in which interword modifications are controlled to form a machine-detectable message in the text document. 18. The apparatus of claim 13 in which said one or more electronic processor is further programmed for modifying spaces between text characters to encode hidden auxiliary data.