Abstract: The invention describes a method of authenticating radio frequency (RF) transponders (14.1, 14.2, 14.3, to 14,n) in an electronic identification system (10), the system (10) also comprising an associated reader (18) and a verifier (22). At least one transponder encoder (16.1, 16.2) is provided for writing respective first watermark data into a memory arrangement of each transponder (14.1, 14.2, 14.3, to 14.n). A verifier (22) interrogates a selected transponder (14.1) to read data stored in the transponder (14.1), the verifier (22) using the read data to derive from its memory an algorithm and input data from which to derive second watermark data for comparison with the first watermark data and provide a signal indicative of the authentication of the transponder. Alternatively the comparison between the first and second watermark data can take place in the transponder (14.1) which is arranged to provide a signal to the verifier (22) as to the authenticity of the transponder (14.1).

Abstract: An RF electronic identification system (10) is disclosed and claimed. The system includes at least one transponder encoder (14.1) for writing data into a memory arrangement (52) of a selected transponder (1.1) of a plurality of transponders (1.1 to 1.n) adapted to receive data from the at least one encoder. The system further includes at least one verifier (16) for interrogating a selected transponder (1.1) and to read data stored in the transponder. The encoder includes a controller (42) for providing an identification code characteristic of the encoder to form part of the data to be written into the transponder. The verifier includes computing means (56) for extracting the identification code from the data read thereby and for comparing the code to authorized codes. An indicator (18) provides an indication whether the identification code corresponds to any of the authorized codes or not. A method of verifying the authenticity of a transponder is also disclosed and claimed.