In Kara Tech v. Stamps.com, the Court of Appeals for the Federal Circuit (CAFC) vacated the District Court’s judgment finding infringement based on a construction consistent with the claims’ plain language. While the specification repeatedly referenced an electronic encryption key, the claims contained no such limitation. The CAFC noted the claims, not the specification, define the invention, and refused to limit the invention on the basis of a term found only in the specification.

Both parties offered witnesses giving conflicting testimony as to whether a person having ordinary skill in the art would have understood the claims to require the use of an encryption key. Noting that conflicting testimony is common in patent litigation, the CAFC concluded that extrinsic evidence, such as the interpretation of the ordinary skilled person, could not overcome intrinsic evidence, such as the plain meaning of the claim language.

Kara Technology owned US. Patent Nos. 6,505,179 (the ’179 patent) and 6,735,575 (the ’575 patent), which concern technology allowing a customer to print a secured document (such as a stamp or an airline ticket) on a preprinted label sheet with a bar code and serial number. Stamps.com approached Kara to collaborate on a stamp technology based on a personal computer and the parties signed a non-disclosure agreement. After ending its relationship with Kara, Stamps.com launched its own stamp technology based on a personal computer. Kara brought suit alleging patent infringement and breach of the non-disclosure agreement. The District Court found the statute of limitations had run on the breach of the non-disclosure agreement. Following a Markman hearing, a jury found no infringement by Stamps.com on Kara’s patents.

The claim construction dispute turned on whether the security indicia must be created and validated under control of a key contained in the pre-established data. The District Court had construed the disputed terms to require a data key. This construction was based on “the history of secure systems design” requiring a key, as well as the detailed embodiment in the specification describing the use of a key in the preprinted data.

The CAFC reversed this conclusion, looking first to the plain language of the claims. First, the CAFC noted the claims do not state that the pre-established data contain a key, only that the data contain “information.” The pre-established data must only contain information that will be used to create the security indicia, but in no way requires a key. Next, the CAFC viewed the claims of the ’179 and ’575 patents together. None of the claims at issue on appeal recited the term “key,” while all of the other independent claims in the patents required either an “encryption key” or “key data.” Although the specification repeatedly discussed a key embedded in the data, the specification was not enough to limit the clear, broader language used in the claims. Citing Corning Glass Works v. Sumitomo Elec. U.S.C., Inc., (Fed. Cir. 1989), the CAFC reiterated the claims, not the specification, defines the metes and bounds of the invention, and thus the scope of protection.

The CAFC then turned to the expert testimony presented to the District Court. Stamp.com’s expert had testified the language of the patent would indicate to one skilled in the art that the information must contain a cryptographic key, while Kara’s expert had testified that the information need not contain a key. Noting that it is not uncommon in patent cases to have “dueling experts,” the CAFC cited