TQP are currently suing more large companies for using RC4 and SSL/TLS, but the way the patent was awarded confuses me.

From the Cipherlawgroup article linked to:

The application for the ’730 patent was filed on April 23, 1992, and claimed priority as a continuation-in-part to an earlier application filed on Oct. 6, 1989. The ’730 patent was originally issued with only two claims:

  1. A method for transmitting data comprising a sequence of blocks in encrypted form over a communication link from a transmitter to a receiver
  2. The method as set forth in claim 1 further including the step of altering said predetermined number of blocks each time said new key value in said first and said second sequences is produced.

Now, since that 1989 wording, TQP have been allowed to add features to the patent and expand it through continuation and the 1992 additions appear to be the core of the lawsuit.

So if one was searching for prior art, would it need to be found before 1989 or 1992? What is the date of validity of this patent?

  • Actually, this may be a dupe of patents.stackexchange.com/q/571/81 which is a much better question.
    – Rory Alsop
    Commented Nov 7, 2012 at 18:07
  • If you can add the patent number(s) and/or patent lookup links, it will make the question more specific
    – Ron J.
    Commented Nov 8, 2012 at 17:27
  • @RonJ. - the patent number is there in the tag
    – Rory Alsop
    Commented Nov 8, 2012 at 17:31

2 Answers 2


The patent in question is a CIP (continuation in part) of the earlier application. Any claims fully supported by the first filing would need pre 1989 references to be attacked. Any claim not fully supported by the initial filing would only need pre 1992 references to be attacked. Continuation in part allows new matter but the new matter gets the new date.

  • Is there an easy way to pinpoint NEW material (i.e. later date) in the CIP? That is, would it be specified in the patent grant and/or examiner comments? This is a classic NPE trick, ignoring the NEW part of CIP patents and suing based on the original priority date - even if the items being claimed infringed are NEW additions. Chaining a dozen continuations allows them to deliberately confuse the issue.
    – Ron J.
    Commented Feb 16, 2013 at 13:25
  • No generic easy way to tell. But, during examination, the default position of the examiner is that everything is new as of the actual filing date and to get the benefit of earlier dates the burden is on the applicant to show full support in earlier filings in the chain. Many practitioners think CIPs can be a trap for the applicant - the opposite of your concern. But confusion can cut both ways, I imagine.
    – George White
    Commented Feb 16, 2013 at 18:04
  • Also regarding NPEs, they generally have purchased the patents they are asserting from bankrupt companies or individual inventors and the average time from patent grant to sale to NPE to assertion is something like 10 years. So in most cases the NPE is not in a position to direct the prosecution of the application in the first place.
    – George White
    Commented Apr 17, 2013 at 3:20
  • Does this paper (cs.berkeley.edu/~christos/classics/diffiehellman.pdf) published in 1976 (ieeexplore.ieee.org/xpl/…) constitute prior art?
    – Catalin P
    Commented Nov 27, 2013 at 7:40

Claim 1 sounds very much like DES Encryption by IBM (1977), which encrypts a stream in blocks. But it requires a private key, which needs to be kept secret. It seems a very broad description - without detail on how these are implemented its hard to tell how it differs from DES, e.g. is it an asymmetric encryption system?

Claim 2 doesn't make much sense. Does it mean that a new key is produced for each block? Great idea - like a skyhook or tartan paint - it doesn't say how it could work. Do you distribute a new key for each block?

  • This doesn't answer the question, which is "when does prior art need to date from?"
    – Rory Alsop
    Commented Nov 13, 2013 at 15:24
  • Hi, Your answer describes possible prior art for the subject patent. On Ask Patents this would be a good answer for a "Request for Prior Art". The question here is about continuations and it is not a prior art request. Sorry for any confusion. Commented Nov 13, 2013 at 17:53

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