This invention relates to devices for and a method for encrypting and decrypting documents. More particularly, this invention relates to a device for and a method for the encryption of physical documents of a general type, including, but not limited to, handwritten documents and documents with pictures, so that the encrypted documents can be sent to an intended recipient by any of the various methods normally used for unencrypted documents, including facsimile transmission, avoiding the risk of unintended disclosure to unauthorized persons, while permitting a facsimile of the original document to be reproduced by the intended recipient.
Many encryption and decryption systems are known, including optical devices and methods. In many of these systems, the "key" to the encryption and decryption lies in a screen or lens; to decrypt a document or message encrypted with a particular screen or lens requires the use of the same or a corresponding screen or lens to that used to encrypt the document or message. Other cryptographic systems operate only on textual information and cannot preserve visible, non-textual information present in a document, such as pictures, symbols, type fonts, or handwriting characteristics. Other systems relating to the encryption of television images are known, but they do not lend themselves to the creation of paper documents that can be handled and sent via facsimile transmission.
U.S. Pat. No. 3,922,074 (Ikegami et al.) discloses a method of storing or recording identifying information on an identifying element and camouflaging the information by recording it through a lenticular plate. The concealed information can then be identified by observing the recording element through the same information medium at the same position used in the initial recording of the identifying information. To decode this information, a person receiving a document must have a lenticular plate corresponding to the one used for encoding the information. U.S. Pat. No. 3,178,993 (Ferris et al.) also describes an optical cryptographic device that uses a lenticular screen.
U.S. Pat. No. 2,952,080 (Avakian et al.) describes a cryptic grid scrambling and unscrambling method apparatus. In accordance with this invention, certain "bits" or "samples" of the signature are combined and intermixed with non-informational bits, which render the signature unapparent. To decode the information, it is placed under a grid or sectionalizing screen to mask out the non-informational bits. Decoding a document in this fashion requires a particular screen. In encoding the information, certain segments of the document are masked out and thereby lost to permit the mixing of the non-information bits.
U.S. Pat. No. 4,989,244 (Naruse et al.) describes a data encrypting transfer system including a scanner, a data encrypting device for encrypting the image signal, and a data decoder for decoding the encrypted image signal. This system uses a card to key the encryption and decryption device, and describes a card-key protected fax. No intermediate form (i.e., encrypted) document is produced.
It is evident that prior art systems do not address a security problem that is becoming increasingly important with the proliferation of inexpensive telephone facsimile machines and the need for the immediate communication of written information.
Increasingly sensitive information is being sent over fax lines, such as sensitive financial data, international confidential correspondence, personnel information, contracts, and private confidential correspondence. In the past this information would be sent via First Class Mail or its equivalent. Now, some of this correspondence is sent by overnight express companies. Timeliness and cost are sacrificed when using an overnight express company. There are over one million facsimile ("fax") machines are currently in use in the United States alone. Millions of faxes are sent per business day, and the fax machine is starting to replace mailed letters for brief correspondence. There are currently over 100 different brands and thousands of models of fax devices currently in use.
Documents transmitted by facsimile are often handled by people other than the intended recipient, as, for example, when the recipient is a member of a large organization with a centralized facsimile receiving department or mail room. Unlike ordinary mail, facsimiles are sent and arrive open and in full view of those handling and delivering them. As such, confidentiality of plainly visible information contained therein cannot be guaranteed, particularly when a common fax machine is shared for either (or both) sending or transmitting documents. Although textual information contained in a fax could be encrypted, many important documents contain charts, pictures, handwriting and handwritten notations and the like, which are not suitable for ordinary textual encryption.
Fax machines currently exist that provide a privacy feature. Typically, this feature works as follows:
1. The sender goes to the common fax machine with the confidential document.
2. The sender puts the document in the fax machine, and types a password into the machine as well.
3. The fax machine sends the confidential fax to the receiving machine.
4. The recipient must go to the common fax machine, enter the password, and wait for the confidential fax to print out.
This method of sending a confidential fax suffers from a number of problems. Confidential faxes can only be sent to and from specific models of fax machines from certain manufacturers. They cannot be sent between machines from different companies. The sender and recipient may be forced to go into a public area to send and print the confidential fax, unless an entire (and usually expensive) fax machine is dedicated to this function and placed in a more private area. Since these faxes are sent to and from the memory of the fax machines, they are limited in length by the memory available in the fax machine. The procedures for setting up the machines to send in this mode are complicated; therefore, most organizations do not bother to do so unless the need is extensive. In addition, because machines having privacy features are typically more expensive than standard fax machines, a company may have only a limited number, if any, of such machines.