Communisis Plc v The Tall Group of Companies Ltd & Ors

A patent claim must be construed purposively, but the court cannot add limitations or extend the monopoly beyond the language of the claim and the contribution disclosed by the specification. A claim requiring code generation by conversion to a higher base does not extend to every cryptographic process whose output is later displayed in a higher base. The skilled person may be a team reflecting the practical expertise needed in the relevant field. Claims are obvious where the only difference from the prior art is an obvious mathematical or presentational choice. Subject matter consisting solely of a mathematical method is excluded from patentability under the Patents Act 1977. A product using secure hashing rather than base conversion therefore did not infringe, including by equivalents.

The claimant, a manufacturer of cheques and cheque-security systems, owned UK Patent No. GB2512450B concerning a code generated from cheque personalisation data and printed on the cheque. It alleged that the defendants’ competing product infringed method and product claims 1 and 6.

The defendants admitted the relevant acts but denied infringement and counterclaimed for invalidity on grounds of obviousness over Martens, Ehrat and Martin, and excluded subject matter. The principal issues were the identity of the skilled person, construction of the claims, inventive step, patentability and infringement.

1. Skilled person and construction. The skilled addressee included banking and cryptographic expertise. The claims were construed purposively, without using the alleged infringement or prior art as an aid to construction.
2. Meaning of code. “Code” included both reversible/decryptable and irreversible codes. Decryption was not an essential feature of validation.
3. Higher-base conversion. The claim required the code itself to be generated by converting the personalisation data, or a subset of it, to a higher base. It did not cover code generated by any cryptographic technique whose output was subsequently displayed in a higher base. The wider construction would give a monopoly far exceeding the disclosed contribution.
4. Printing and generation. The claim did not require the whole generated code to be printed. “During generation” covered printing at any point in the process of producing a cheque or credit instrument containing the information necessary for presentation to a bank.
5. Obviousness. Applying the Windsurfing/Pozzoli approach and the statutory question under section 3 of the Patents Act 1977, the only material difference between the prior art and the claims was conversion to a higher base. That was obvious to the skilled person, even though the skilled person would likely prefer stronger cryptography. Claims 1 and 6 were therefore obvious over Martens, Ehrat and Martin.
6. Excluded subject matter. Applying the four-stage Aerotel test, the alleged contribution was no more than encryption by conversion to a higher base. It was therefore a mathematical method excluded under section 1(2)(a) of the Patents Act 1977.
7. Infringement. The defendants’ product used a secure hashing function. Conversion of the hash output to hexadecimal was merely presentational. The product therefore did not generate a code by conversion to a higher base and did not infringe on a normal construction. There could be no infringement by equivalents because the alleged broader inventive concept was neither inventive over the prior art nor patentable.
8. Disposition. Claims 1 and 6 were invalid for obviousness and excluded subject matter. The infringement claim was dismissed.