Method for operating a data transmission system comprising a transponder and a reading device.

p0001The invention relates to a method according to the preamble of patent claim 1. Such a method is known from EP 0521547 A1.

p0002For the transmission of encrypted electronic data are data transmission systems from a battery-powered infrared (IR / RF) remote control transmitter module and a receiver module suitable use. In addition, more recently, Data Transmission of transponder and reader are used, in which inductive coupling first energy transfer between the reader and tag, and then a data transmission between the transponder (transmitter) and the reader (receiver) is performed. Such data transmission systems are in particular in the automotive sector as a combination of electronic key (transponder) and electronic lock (reader) on the operation of locking and anti-theft devices in the form of immobilisers increasingly on the market. (Typ. 100 kHz to 450 kHz), the data transmission in the RF range between essentially of an integrated circuit (IC) and a coil current transponder and the reader can be done in two ways: either unidirectional means of a fixed code transponder, which in each read operation (at each data transfer) a in a read only memory (PROM) of the IC transmits programmed constant code as a password or bidirectionally by means of a "read / Write" -Transponders which at each read operation (at each data transfer) a in a read / write memory (EEPROM) transfers of ICs stored variable code as the password and after successful authentication by the reader receives a new code and enters into the EEPROM. The disadvantage here is that for a fixed-code data transmission through unauthorized reading of the code an abuse is easily possible (for example, a motor vehicle can be started with an appropriately programmed transponder replica as often), whereas in a changing code data transmission misuse by unauthorized reading indeed is largely excluded, but this is significantly more expensive and due to the relatively high energy requirement has a limited range.

p0003In the method described in EP 0521547 is carried out a verification process through a bidirectional communication between the arranged in a motor vehicle reader and the transponder at each data transfer by following the activation of the reader of this as a reader message a reader password in plain text this reader password is transmitted to the transponder, received by the transponder, compared with a stored in the transponder transponder fixed code and a verification is performed by the transponder for a match of reader password and transponder fixed code; in the case of their compliance further verification process at the reader is then additionally performed by transmitting a transponder message a transponder password in clear text to the reader and this will be reviewed in the reader to match a stored in the reader reader hard code. Since the transmission of data (passwords) always is in plain text, a protection against misuse by unauthorized listening or reading is not guaranteed without gaps.

p0004The invention is based on the object, a method according to the preamble of claim 1 indicate in which a high abuse security exists and a cost effective data transmission with advantageous properties - is possible - particularly as regards energy consumption and range. This object is achieved by the characterizing features of claim 1. Advantageous developments and refinements of the method are evident from the dependent claims.

p0005The verification of the secret, non-readable fixed code (communication key) of reader and transponder carried by a bidirectional data transfer between the reader and tag by cryptologic protocols; ie the agreement of reader-fixed code and transponder fixed code is indirectly checked and verified by exchanging encrypted reader messages or transponder messages. The transmission of messages, their review, the verification process can be done in different ways:<ul><li>as reader-message a one- time reader random number is first transmitted to the transponder, for example, generated by a functioning as a pseudo-random algorithm; the transponder is generated from this reader-random number and of acting as a key transponder fixed code using a stored algorithm or by electronically linking a transponder ciphertext and this is transmitted as first transponder message to the reader. In reader a reader-ciphertext is generated or vice versa decrypts the first transponder message again either by the same procedure as in the transponder, which by establishing the reader hard code is the key; a verification is carried out either for a match of the transmitted transponder ciphertext with the reader secret text or for a match of the decrypted result to the reader random number.</li><li>by additional authentication protocols between the reader and tag can be increased against eavesdropping: in the transponder can be an own transponder random number generated and linked to the reader random number transmitted by the reader to a secret random number; this secret random number is encrypted using the transponder fixed code as the key to transponder ciphertext. The transponder random number is transmitted to the reader either transmitted by means of a second transponder message in plain text or encrypted with a transponder key; the reader this secret random number (if applicable after decoding with a reader-key) generated with knowledge of the transponder random number by reference to the reader-random number, the secret random number, encrypted by the reader-fixed code to the reader-ciphertext and this in accordance checked with the transponder ciphertext or vice versa decrypts the transponder ciphertext with the reader-fixed code and checks the result for compliance with the secret random number.</li></ul>

p0006After successful authentication between transponder and reader which is connected to the reader via communication lines control units can be unlocked - preferably by two-way communication in cryptologic protocols; For example, the data is used on the communication lines as a control signal for locking / unlocking the immobilizer of a motor vehicle in the engine control unit: the ignition is turned off and remains, for example, eliminated more than 15 seconds, all the control devices and the reader will be blocked; then the above-described method of cryptologic data transmission must be repeated. The reader can also be part of another control unit of the motor vehicle, for example, a component of the engine control unit. As with any data transmission, a verification process is performed by bidirectional communication via secret cryptologic protocols between the reader and tag, a high privacy or security is given against abuse (due to unauthorized reading); (For example, stored in a PROM) by using a fixed code in the reader and the transponder can also be realized at the same time a low-cost transfer process with low energy consumption and consequently a relatively large range.

p0007The process is described below with reference to the drawing: in the figure, a data transmission system for a "CryptoLogic" is shown data transmission method.

p0008According to the figure, the transponder 1 from the coil 11 for transmitting power and data transmission as well as the integrated circuit (IC) 10; the IC 10 includes a control unit 12 to the power supply and sequencer, a memory unit 13 - in this (for example, in a PROM) of non-readable, secret transponder fixed code TFC stored -, a random 14 - of this (for example, by a certain algorithm) the transponder random number TZZ generated - and an encryption unit 15 for generating the transponder ciphertext TGT from the reader random number LZZ or from those obtained by linking reader random number LZZ and transponder random number TZZ secret random number GZZ with the transponder fixed code TFC as the key. The reading device 2 is composed of the coil 21, which simultaneously serves for energy transmission and for data transmission from the control unit 22 to control flow from the random generator 24 for generating the reader random number LZZ, from the storage unit 23 for storing the secret, non-readable reading device -Festcodes LFC and from the encryption unit 25 for generating the reader-ciphertext LGT from the reader random number LZZ or from those obtained by linking reader random number LZZ and transponder random number TZZ secret random number GZZ with the reader hard code LFC as a key. After activation of the reader 2 - for example in a motor vehicle by operating the door handle or by turning on the ignition - is as reader-message LN for example CryptoLogic generated in the random number generator 24 reader-random number LZZ of the coil 21 - After the activation of the transponder 1 result inductive energy transmission from the reader-coil 21 to transponder coil 11 - the transponder 1 transmits (in the cryptologic generation of reader-random number LZZ a counter is stored in the storage unit 23, which for the random number generator 24 with the reader hard code LFC as a key reader-random number LZZ is encrypted; by incrementing the counter of the new count in the storage unit 23 is stored and thus the uniqueness of the reader random number LZZ ensured). With the data stored in the storage unit 13 of the transponder 1 transponder fixed code TFC is determined by the encryption unit 15, either the reader random number LZZ or by linking reader random number LZZ and generated by the random number generator 14 transponder random number TZZ (for example, a bitwise XOR linkage of the random numbers and LZZ TZZ) obtained secret random number to the transponder GZZ encrypted ciphertext TGT. This transponder ciphertext TGT is transmitted as a first transponder message TN1 to the reading device 2 is received by the coil 21 of the reader 2 and verified from the generated reader ciphertext LGT from the control unit 22 of the reading device 2 by comparison with a in the reader 2, which was won by either encrypting the reader random number generated by the random number generator 24 LZZ or by encryption with the reader 2 of reader-random number LZZ and transponder random number TZZ with the data stored in the storage unit 23 reader-fixed code LFC generated as a key secret random number GZZ. To generate the secret random number GZZ by the reader 2, the transponder random number TZZ the reader must be known 2; this is from the transponder 1 prior to or subsequent to the first transponder message TN1 (transponder ciphertext TGT) encrypted to the reader 2 through a second transponder message TN2 either in plain text or by means of a transponder key (in this case, they must by be reader 2 decoded by a reader-key) transmitted - the transponder key or reader key is chosen preferably different from both the first key used fixed code (transponder fixed code TFC or reader hard code LFC). If a match of transponder ciphertext TGT and reader-ciphertext LGT data transfer is verified to be valid; then the reader 2 an encodable output AS can (for example via communication lines connected) control units - preferably in bidirectional cryptologic protocols - unlock.