Method for protecting content using watermarking

An access control method, comprising the steps of:

• during a watermarking phase:
• generating a first digital string from an object sought to be protected to form a baseline watermark;
• generating a second digital string from given text;
• generating a watermark having a predetermined relationship to the first and second digital strings;
• and
• inserting the watermark into the object to protect access to the object;
• upon an access request:
• retrieving a derived watermark from the object to form a third digital string;
• generating a fourth digital string from the given text;
• correlating the third and fourth digital strings;
• and
• if the third and fourth digital strings have a predetermined correlation, authorizing access to the object.

A method of watermarking an object, comprising the steps of:

• generating a first digital string from the object to form a baseline watermark;
• generating a second digital string from given text providing an indication that a first action with respect to the object is allowed and a second action with respect to the object is prohibited;
• generating a watermark having a predetermined relationship to the given text and the second digital string;
• and
• inserting the watermark into the object.

A method for determining whether an object has a given watermark, comprising the steps of:

• processing the object to generate a data string;
• correlating the data string with a value that is a function of the given watermark and a second watermark such that information useful in determining the given watermark cannot be obtained from the value;
• and
• if the data string and the value correlate to a predetermined extent, indicating that the object has been watermarked with the given watermark.

A access protection method operative in a device having means for outputting given content, comprising the steps of:

• retrieving a derived watermark and a derived signal from the given content;
• generating a digital string from the derived signal using a secure hash function;
• correlating the derived watermark and the digital string;
• and
• based on a result of the correlating step, taking a given action.

A method for authorizing access to given content that has a given watermark embedded therein, comprising the steps of:

• processing the given content to generate a first data string;
• generating a second data string by applying a given function to the first data string;
• correlating the first and second data strings;
• and
• if the first and second data strings correlate to a given degree, providing a password to enable further processing of the given content.

A method for computing a derived watermark, comprising the steps of:

• processing a given work W to form a first data string x.sub.1, x.sub.2, . . . x.sub.n,
• processing a collection C of works to form a second data string y.sub.1, y.sub.2, . . . y.sub.n ;
• and
• computing the derived watermark z.sub.1, z.sub.2, . . . z.sub.n by applying a given function f(x.sub.i, y.sub.i).

A method of access control for a document, comprising the steps of:

• generating a first digital string from the document to form a baseline watermark;
• generating a second digital string from given text;
• generating a set of watermarks each having a predetermined relationship to the first and second digital strings;
• and
• inserting the set of watermarks into the document to protect the document against illicit use.

A method for detecting a watermark in a document using information that, if disclosed, does not compromise security of the document, comprising the steps of:

• processing the document to generate a data string;
• correlating the data string with the information;
• and
• accepting the document as including the watermark if the data string and the information correlate to a predetermined extent.