An RFID tag comprising a) a transmitting device and a receiving device of data of a reader, b) a memory for identification data uniquely characterizing the RFID tag, c) a control means, which automatically executes functions depending on that the reader - proves the knowledge of an internal password in a memory for the internal password by means of a comparison, and/or - allows information stored in the memory for an internal state to execute the function, d) a first comparison means for comparing two values; e) a changing means for changing the stored password and/or the internal state depending on a previous comparison of the internal password with one received by the reader (f) a randomizer for generating random values, (g) a test value means for calculating one or more test values form at least two input values, (h) a volatile or non-volatile, rewritable buffer for buffering a random value, and (i) a non-volatile and non-rewritable memory for storing a secret value, characterized in that a challenge-response function for verifying the identification data is provided by using a random value received by the reader and the secret value as an input of the test value means and transmitting the result back to the reader, wherein the authenticity of identification data transmitted by an RFID tag can be verified with the help of the manufacturer by means of the result, and wherein the challenge-response function is also intended for comparing the stored internal password by answering a request of the reader to compare the stored password with buffering and transmitting a random value generated with the randomizer, wherein the response of the reader to the transmission of the random value is compared to the result of the test value means, wherein the values from the buffer of the random value and from the memory of the internal password are used as an input of the test value means, or wherein the response of the reader to the transmission of the random value and this result of the test value means are used as an input for the first comparison means. a) a transmitting device and a receiving device of data of a reader, b) a memory for identification data uniquely characterizing the RFID tag, c) a control means, which automatically executes functions depending on that the reader - proves the knowledge of an internal password in a memory for the internal password by means of a comparison, and/or - allows information stored in the memory for an internal state to execute the function, - proves the knowledge of an internal password in a memory for the internal password by means of a comparison, and/or - allows information stored in the memory for an internal state to execute the function, d) a first comparison means for comparing two values; e) a changing means for changing the stored password and/or the internal state depending on a previous comparison of the internal password with one received by the reader (f) a randomizer for generating random values, (g) a test value means for calculating one or more test values form at least two input values, (h) a volatile or non-volatile, rewritable buffer for buffering a random value, and (i) a non-volatile and non-rewritable memory for storing a secret value, characterized in that