[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Motorola patent 5,130,993 on checksum of encoded data


Bill:

The earliest description of CBCC that I have was published in April 1984.  
The algorithm description is in section 5.2 of the Xerox Network System 
(XNS) Authentication Protocol specification.  The text says:

     The Authentication Protocol uses a variant of the standard cipher 
     block chaining mode in which the XOR sum of plain text blocks 1 
     through n-1 is XORed with the plain text block n before encryption.  
     This makes it possible to detect tampering with the cipher text.  This 
     mode of DES, called cipher block chaining with checksum (CBCC), is 
     shown in Figure 5.2.

I should have dug out the document before I made my original posting about 
CBCC.  I did not remember the details correctly.  As you can see from the 
above text, the plaintext is summed, not the ciphertext.

There is a notice in the front of the book that says:

     This standard includes subject matter relating to patent(s) of Xerox 
     Corporation.  No licensee under such patent(s) is granted by 
     implication, estoppel, or otherwise, as a result of the publication of 
     this specification.

I do not know if CBCC is patented or not.  Perhaps someone employed by 
Xerox can tell us.

Someone else will have to decide if this work can be used to challenge 
Motorola's claim. I do not know if the document is still available from 
Xerox, but here is the information from the front about ordering:

     Xerox Corporation
     Office Systems Division
     Network Systems Administration Office 
     3450 Hillview Avenue
     Palo Alto, CA 94304

     Authentication Protocol
     XSIS 098404
     April 1984

I know that Xerox still has a facility on Hillview in Palo Alto, but the 
Xerox Corporation has be reorganized many times since 1984, and the Office 
Systems Division does not exist anymore.

Bill, if you want me to fax you Section 5.2, send me a fax phone number.

Russ