DE10223217A1 - A method of encoding data packets in wireless networks, involves use of first and second counters for counting data packets and data blocks - Google Patents

Abstract

A method for encrypting/encoding data packets in which the data packets comprise data blocks and in which the data packets are counted by a first counter and the data blocks are counted by a second counter, and a cryptographic bit sequence is ascertained, while for the data block a combined counter is formed from the first and second counters and is combined with a key with a cryptographic algorithm. The data packets are then encrypted /encoded by the cryptographic bit sequence. (A) A method for decoding data packets. (B) An arrangement for encoding data packets. (C) An arrangement for decoding data packets.

Description

The invention relates to a method and an arrangement for Encryption and a method and an arrangement for Decryption of data packets in wireless networks.

From [1] is a wireless local area network (Wireless Local Area Network, WLAN), where data is both Voice data as well as multimedia data can be wireless can be transmitted by radio or infrared. This WiFi connects different components, e.g. B. computers, screens, wireless phones or radios with each other. The spatial The extent of the WLAN is limited by its radio range.

Standard specifications for the WLAN are known from [2], z. For example, a HomeRF standard or an IEEE802.11b standard which each have a Medium Access Control Protocol (MAC Protocol) a communication between different Components of the WLAN regulates by each component of the WLAN one own address for their identification, a so-called Medium Access Control address (MAC address).

From [3] a symmetrical block cipher is based on the "Advanced Encryption Standard" (AES) known in different so-called modes can be operated. In [4] is a counter mode (CTR mode) for AES explained, in which with a counter and a cryptographic key a random number sequence is generated in blocks, which leads to a block-by-block encryption of a data sequence is used. In [5] is an extended cipher block chaining mode Generation of a message authentication code (XCBC-MAC mode) for AES explains, with the help of two cryptographic Key a checksum of a data sequence is generated. This check sum can be used to change the data sequence be recognized after a transmission.

The special one is when transmitting data by radio Disadvantage that unauthorized third parties access the data to eavesdrop on or manipulate them. To this To prevent unwanted access, the data is shared with encrypted cryptographic procedures. Previous Procedures such as the HomeRF standard or the IEEE802.11b standard, use counters to encrypt the data Counter values with an average data traffic multiply repeat for a day or a short period of time. These methods therefore offer possibilities for the illegal Third-party access to the data and are accordingly uncertain. Furthermore, these methods have the disadvantage that manipulation of the data is not noticed.

The invention is therefore based on the object Security of data transmission in wireless networks too increase.

This task is carried out according to the characteristics of the independent Claims resolved. Developments of the invention result also from the dependent claims.

An encryption method is used to solve the problem of data packets in a wireless network. The Data packets include several data blocks. The Data packets are based on a first counter and the data blocks counted using a second counter. A cryptographic Bit sequence is determined in that for each data block one from the first and from the second counter composite counter with a key with a cryptographic Algorithm is linked. The data packets are based on this cryptographic bit sequence is encrypted.

In addition, the task is accomplished through a process for Decryption of data packets in a wireless network solved. The data packets include several data blocks. The data packets are based on a first counter and Data blocks counted using a second counter. A cryptographic bit sequence is determined in that for each Data block on from the first and from the second counter composite counter with a key with a cryptographic algorithm is linked. The data packets are based on this cryptographic bit sequence decrypted.

An advantage of the invention is that the composite counter has a greater bit length than each single counter. In this way, the composite counter higher counter readings achievable, which at Encryption of the data packets to fewer repetitions of the Counter values themselves. So the encrypted Data packets during transmission against interception and Manipulation attempts by third parties are safer than with meters lower maximum counter readings (shorter counters) at which naturally more frequent repetitions of the individual counter values occur.

A further development is that the first counter is sent in addition to the encrypted data packet.

Accordingly, further training consists in the first Counter together with the respective encrypted data packet is received and evaluated.

This has the advantage that the first counter that is used for Decryption of the encrypted data packet is necessary, is directly available for decryption and not otherwise transferred or determined.

Another training is that a first cryptographic checksum based on the first counter and the encrypted data packet is determined. This first cryptographic checksum is together with the first counter and transmit the encrypted data packet.

One related training course is that this is first cryptographic checksum together with the first counter and the encrypted data packet is received. A second cryptographic checksum is received for the first one Counter and the encrypted data packet received determined. The authenticity of the encrypted received Data packet is compared by comparing the first with the second checked cryptographic checksum. In the case of one If both checksums match, the authenticity of the Data packet accepted and otherwise the authenticity of the Data packet not accepted.

This has the advantage that manipulations by third parties on the encrypted data packets or recognized at the first counter become.

The next one will be the first cryptographic checksum for the first counter and the encrypted Data packet according to an XCBC-MAC mode of "Advanced Encryption Standards "(AES) determined.

In an associated training course, the second cryptographic checksum for the first counter and that encrypted data packet according to the XCBC-MAC mode of the AES determined.

This is advantageous in that the XCBC MAC Mode of the AES to a particularly safe and recognized Process for generating checksums, so that a successful and therefore undetected manipulation Third is unlikely.

Another training is that the composite counter public and the cryptographic key is secret. In this way the exchange of information between components or participants or instances of the wireless network simplified as far as the counters themselves do not have to be encrypted.

In a next development, the second counter starts each data packet with a predetermined initial value, e.g. B. with the value "0" or "1". This has the advantage of being a count automated of the data blocks with the help of the second counter runs and thus a corresponding protocol level on Counting the data packets themselves can be restricted.

In one development, the wireless network is a local one Network, especially a HomeRF network. According to the invention becomes the previous counter of the HomeRF standard in particular replaced by the composite counter, which is the first Counter, which counts the data packets, and the second counter, which counts the data blocks. Therefore, counting the Data blocks automated with the help of the second counter and thus the corresponding HomeRF protocol level on one count of the data packets themselves are restricted. Beyond that a functional extension of the existing Protocol architecture, in particular the MAC protocol layer of the HomeRF Standards possible, so that the XCBC-MAC mode of the AES for Generation of a checksum can be used. Accordingly based on the present invention in the HomeRF network for the first time the performance of a proof of authenticity for the transmitted data packets possible.

Another training is that the composite counter has at least a length of 128 bits. Compared to the previously used counter lengths of 32 bits HomeRF networks or 24 bit for IEEE802.11b networks with a counter length of at least 128 bits the period up to for a repetition of the counter values significantly extended and in this way the security of data transmission clearly increased.

In a next development, the second counter is on one predefined maximum number of data blocks adapted, such that the length of the second counter is unique Enables counting the maximum number of data blocks. On this way the bit length given to the second counter is assigned to be kept to the minimum value. There the first and the second counter are advantageous Divide the specified length of the composite counter is shown optimized design of the second counter the first counter a maximum bit length is available. This will increase the number of the data packets maximized over the wireless local Network can be transferred before a value of the repeated first counter.

In a further development, the second counter has one Length of 7 bits. As a result, the length of the second counter is on the maximum number of data blocks in a data packet HomeRF network adapted. Then stand for the first counter with a length of the combined counter of 128 bits still 121 bits available.

It should be noted here that the lengths of the counters mentioned are exemplary; other meter lengths are also possible, z. B. if an adaptation to another standard or increased security requirements make this necessary. In addition, meter and key lengths are in the significantly different orders of magnitude, e.g. B. in a length of several 100 or 1000 bits, possible and depending on the application appropriate.

Another training consists of the first Counter is a HomeRF counter. This is an adjustment of the invention particularly easy for a HomeRF network feasible.

In a next development, the first counter comprises one MAC address. Using this MAC address, the individual Components of the wireless local area network, the transmitter of an encrypted data packet is clearly identified become.

In a next training course, the key at least 128 bits in length. In a HomeRF network the key length can be a maximum of 128 bits, in IE For EE802.11b networks, the key length is 40 bits.

In a next development, a block of cryptographic bit sequence at least a length of 128 bits.

Another training is that the cryptographic algorithm a cryptographic algorithm according to the "Advanced Encryption Standard" (AES). This is insofar as it is the cryptographic AES algorithm for a particularly secure and recognized encryption and decryption algorithm is about data packets, so that when it is used, a Third-party manipulation is extremely unlikely.

In a next training, a cryptographic AES algorithm operated in a CTR mode. in this connection The particular advantage is that the AES algorithm in the CTR mode a cryptographic key with a Length of 128 bits and a counter with a length of 128 Bit used, so in this case no further adjustment is necessary. In particular, a functional extension of the existing protocol architecture, especially the MAC Protocol layer of the HomeRF standard possible so that the AES algorithm, operated in CTR mode, for encryption which data can be used.

Furthermore, an arrangement for Encryption of data packets in a wireless network specified. In this arrangement there is a processor unit provided that is set up such that the data packets Include data blocks. The data packets are based on a first counter and the data blocks based on a second counter countable. This creates a cryptographic bit sequence ascertainable that for each data block one from the first and from the second counter composite counter with a key is linked to a cryptographic algorithm. The Data packets are with this processor unit based on the cryptographic bit sequence can be encrypted.

In addition, an arrangement for Decryption of data packets in a wireless network specified. In this arrangement there is a processor unit provided that is set up such that the data packets Include data blocks. The data packets are based on a first counter and the data blocks based on a second counter countable. This creates a cryptographic bit sequence ascertainable that for each data block one from the first and from the second counter composite counter with a key is linked to a cryptographic algorithm. The Data packets are with this processor unit based on the cryptographic bit sequence can be decrypted.

The arrangements are particularly suitable for implementation the method according to the invention or one of the above explained further training.

Also, the invention or any of those described above Continuing education realized by a computer program product be, which has a storage medium on which a Computer program is stored on a computer is executable and carries out the invention or further development.

Exemplary embodiments of the invention are described below of the drawings shown and explained.

Show it

Fig. 1 is a diagram illustrating a method for encrypting a data packet,

Fig. 2 shows the structure of a wireless network,

Fig. 3 is a diagram illustrating a method for decoding a data packet,

Fig. 4 is a flowchart for batch processing of a data packet with a checksum before sending,

Fig. 5 is a flowchart for batch processing an encrypted data packet with authentication after receiving it,

Fig. 6 is a processor unit.

In Fig. 1, a sketch is shown, illustrating a method for encrypting data packets.

The encryption of a data packet 101 is shown, which by way of example comprises three data blocks 102 , 103 and 104 , each with a length of 128 bits. A first counter 108 with a length of 121 bits counts data packets and is set with the data packet 101 as an example to the value "23", ie the first counter 108 has the value "23" for the data blocks 102 to 104 . A second counter 109 with a length of 7 bits counts the data blocks 102 to 104 , ie for the data block 102 the second counter 109 has an initial value "0", for the data block 103 the second counter 109 assumes the value "1" and takes it with it In the last data block 104 , the second counter 109 receives the value "2". For data block 102, this results in a counter value 105 composed of the first counter 108 and the second counter 109 "23" and "0", which is coded in a field with a length of 128 bits. According to the same scheme, a composite counter value 106 results for data block 103 and a composite counter value 107 for data block 104 .

The composite counter value 105 is shared with a secret key K, which has a length of 128 bits, a cryptographic algorithm A, e.g. B. according to an AES in a CTR mode, and thus a block 110 of a cryptographic bit sequence 113 is generated. The data block 102 is linked to the block 110 "Exclusive-OR" XOR, so that an encrypted data block 114 is created. Correspondingly, the composite counter value 106 together with the key K is subjected to the algorithm A and in this way a block 111 of the cryptographic bit sequence 113 is generated. The data block 103 is linked with this block 111 "Exclusive-OR" XOR, so that an encrypted data block 115 is created. Likewise, the composite counter value 107 is subjected to the algorithm A together with the key K, and in this way a block 112 of the cryptographic bit sequence 113 is generated. The data block 104 is linked with this block 112 "Exclusive-OR" XOR, so that an encrypted data block 116 is created. In this way, an encrypted data packet 117 is generated from the data packet 101 , which includes the encrypted data blocks 114 , 115 and 116 .

Before the encrypted data packet 117 is sent, the first counter 108 is added to it.

In FIG. 2, the construction of a wireless network N is illustrated. The network N comprises a transmitter S, a radio channel F and a receiver E. In the transmitter S, data packets, as explained in FIG. 1, are encrypted in an encryption unit VS. These encrypted data are sent by a transmitting unit SE of the transmitter S via the radio channel F and received by a receiving unit EE of the receiver E. The data packets are decrypted in a decryption unit ES of the receiver E, which is explained in more detail below in FIG. 3. Unauthorized third parties can receive the encrypted data packets through a listening device A in radio channel F and, if necessary, try to manipulate them. Eavesdropping on (confidential) information, ie possible decryption within the eavesdropping device A, as well as manipulation of the transmitted data within the eavesdropping device A are attacks which the methods and arrangements described here have as their countermeasure. In particular, against the background of possible manipulation for the receiver E, it is important to know whether the data received via the radio channel actually originate from the transmitter S or whether the transmitter S cannot be authenticated as the sender. In the second case, manipulation of the data would have been discovered by determining that the data were not originally sent by the transmitter S.

FIG. 3 shows a sketch which illustrates a method for decrypting data packets.

The decryption of an encrypted data packet 301 , which was received together with a first counter 308 , is shown here by way of example. The encrypted data packet 301 comprises three encrypted data blocks 302 , 303 and 304, each with a length of 128 bits.

The first counter 308 with a length of 121 bits counts data packets and has the value "23" for the encrypted data packet 301 as an example, ie the first counter 308 has the value "23" of the data packet 301 for the encrypted data blocks 302 to 304 . A second counter 309 with a length of 7 bits counts the (still encrypted) data blocks 302 to 304 , ie for the encrypted data block 302 the second counter 309 has an initial value "0", for the encrypted data block 303 the second counter 309 receives the value "1" and for the last encrypted data block 304 , the second counter 309 receives the value "2". For the encrypted data block 302, this results in a counter value 305 composed of the first counter 308 and the second counter 309 and having a length of 128 bits. Accordingly, a composite counter value 306 results for the encrypted data block 303 and a composite counter value 307 for the encrypted data block 304 .

A secret key K with a length of 128 bits is used both for the encryption of data packets, as shown in FIG. 1, and for the decryption shown here. For this purpose, the key K is to be made known both on the side of the transmitter and on the side of the receiver. Likewise, the same cryptographic algorithm A is used in the cases of encryption and decryption.

The composite counter value 305 is fed together with the key K to the cryprographic algorithm A and thus a block 310 of a cryptographic bit sequence 313 is generated. The encrypted data block 302 is linked with this block 310 "Exclusive-OR" XOR, so that a data block 314 is created which, according to the present example, is the same as the data block 102 from FIG. 1.

Correspondingly, the composite counter value 306 is fed to the algorithm A together with the key K and thus a block 311 of the cryptographic bit sequence 313 is generated. The encrypted data block 303 is linked with this block 311 "exclusive OR" XOR, so that a decrypted data block 315 is created. Likewise, the composite counter value 307 is fed to the algorithm A together with the key K and thus a block 312 of the cryptographic bit sequence 313 is generated. The data block 304 is linked with this block 312 "exclusive-OR" XOR, so that a decrypted data block 316 is created. In this way, the encrypted data packet 301 becomes a decrypted data packet 317 , which comprises the decrypted data blocks 314 , 315 and 316 and, according to the example chosen here, has the same data blocks as the data packet 101 from FIG. 1 after the decryption described.

In FIG. 4 is a flowchart for the batch processing of a data packet represented by checksum before sending transmitter to receiver, via a radio network.

A data packet 401 is subjected to encryption 402 , as explained in FIG. 1. A first counter 403 used here is added to the encrypted data packet 404 . The encrypted data packet 404 and the first counter 403 are subjected to a first checksum formation 405 , e.g. B. according to AES in XCBC-MAC mode, to enable an authenticity check of the data packet 404 when received. A resulting checksum 406 is added to the encrypted data packet 404 with the first counter 403 and all three parts are fed together to a sending unit 407 .

FIG. 5 shows a flowchart for batch processing an encrypted data packet with authenticity verification after receipt.

After receiving in a receiving unit 501 , an encrypted data packet 502 is present together with a first counter 503 and a first checksum 504 . The encrypted data packet 502 , together with the first counter 503, is subjected to a second checksum formation 505 , which here corresponds to the first checksum formation from FIG. 4. The second checksum 506 obtained from the second checksum formation is compared with the first checksum 504 in a comparison procedure 507 . If the two do not match, it is proven that either the encrypted data packet 502 and / or the first counter 503 has / have been manipulated and the processing is terminated with a warning message 510 about a possible manipulation. If the first checksum 504 matches the second checksum 506 , the authenticity of the encrypted data packet 502 and the first counter 503 is verified and the data packet 502 can be decrypted. For this purpose, the data packet 502 is subjected to a decryption procedure 508 , as explained in FIG. 3, the first counter 503 being used in the manner described in FIG. 3. The decrypted data packet 509 emerges from the decryption procedure.

In FIG. 6, a processor unit PRZE. The processor unit PRZE comprises a processor CPU, a memory MEM and an input / output interface IOS, which is used in different ways via an interface IFC: an output is visible on a monitor MON and / or on a printer via a graphic interface PRT issued. An entry is made using a mouse MAS or a keyboard TAST. The processor unit PRZE also has a data bus BUS, which ensures the connection of a memory MEM, the processor CPU and the input / output interface IOS. Furthermore, additional components can be connected to the data bus BUS, e.g. B. additional memory, data storage (hard disk) or scanner. Bibliography [1] "What is a Wireless LAN?", Http: / / www.proxim.com/learn/library/whitepapers/pdf/whatw lan. pdf
[2] "A Comparison of Security in HomeRF versus IEEE802.11b", http: / / www.homerf.org/data/tech/security-comparison.pdf
[3] National Institute of Standards and Technology: "Modes of Operation for Symmetric Key Block Ciphers", http: / / csrc.nist.gov/encryption/modes
[4] H. Lipmaa, P. Rogaway, D. Wagner: "Comments to NIST concerning AES Modes of Operations: CTR-Mode Encryption", http: // csrc.nist.gov/encryption/modes/proposedmodes/ctr/c tr-spec.pdf
[5] J. Black, P. Rogaway: "Comments to NIST concerning AES Modes of Operations: A Suggestion for Handling Arbitrary-Length Messages with the CBC MAC", http: / / csrc.nist.gov/encryption/modes/proposedmodes /xcbc/xcbc-spec.pdf

Claims (22)

1. method for encrypting data packets in a wireless network, in which the data packets comprise data blocks, in which the data packets are counted using a first counter, in which the data blocks are counted using a second counter, - in which a cryptographic bit sequence is determined by linking a counter composed of the first counter and the second counter with a key to a cryptographic algorithm for the data block, and - In which the data packets are encrypted using the cryptographic bit sequence. 2. The method according to claim 1, where the first counter is in addition to that encrypted data packet is transmitted. 3. The method according to claim 1, in which a first cryptographic checksum based on the first counter and the encrypted data packet is determined and the first cryptographic checksum along with the first counter and the encrypted one Data packet is transmitted. 4. The method according to claim 3, where the first cryptographic checksum for the first counter and the encrypted data packet according to a XCBC-MAC mode of the Advanced Encryption Standard is determined. 5. method for decrypting data packets in wireless networks, in which the data packets comprise data blocks, in which the data packets are counted using a first counter, in which the data blocks are counted using a second counter, - in which a cryptographic bit sequence is determined by linking a counter composed of the first counter and the second counter with a key to a cryptographic algorithm for the data block, and - In which the data packets are decrypted using the cryptographic bit sequence. 6. The method according to claim 4, where the first counter is in addition to that encrypted data packet is received. 7. The method according to claim 4, the first counter is received together with the data packet and a first cryptographic checksum, a second cryptographic checksum for the first counter and the encrypted data packet is determined, in which an authenticity of the received data packet is checked by comparing the first cryptographic checksum with the second cryptographic checksum, and - In which, if the two checksums match, the authenticity of the data packet is assumed and otherwise the authenticity of the data packet is not accepted. 8. The method according to claim 7, where the second cryptographic checksum for the first counter and the encrypted data packet according XCBC-MAC mode of the Advanced Encryption Standard is determined. 9. The method according to any one of the preceding claims, where the composite counter is public and the cryptographic key is secret. 10. The method according to any one of the preceding claims, with which the second counter with each new data packet starts at a predetermined starting value. 11. The method according to any one of the preceding claims, where the wireless network is a HomeRF network. 12. The method according to any one of the preceding claims, where the composite counter is at least one length of 128 bits. 13. The method according to any one of the preceding claims, in which the second counter to a predetermined maximum Number of data blocks is adapted such that the Length of the second counter a clear count of the allows maximum number of data blocks. 14. The method according to any one of the preceding claims, where the second counter has a length of 7 bits. 15. The method according to any one of the preceding claims, where the first counter is a HomeRF counter. 16. The method according to any one of the preceding claims, in which the first counter comprises a MAC address. 17. The method according to any one of the preceding claims, where the cryptographic key is at least one 128 bits long. 18. The method according to any one of the preceding claims, in which a block of the cryptographic bit sequence has a length of at least 128 bits. 19. The method according to any one of the preceding claims, where the cryptographic algorithm cryptographic algorithm according to an advanced encryption Standard (AES) is. 20. The method according to claim 15, in which the cryptographic algorithm according to a Advanced Encryption Standard operated in a CTR mode becomes. 21. Arrangement for encrypting data packets in a wireless network, in which a processor unit is provided which is set up in such a way that the data packets comprise data blocks, the data packets can be counted using a first counter, the data blocks can be counted using a second counter, a cryptographic bit sequence can be determined by linking a counter composed of the first counter and the second counter with a key to a cryptographic algorithm for the data block, and - The data packets can be encrypted with this processor unit using the cryptographic bit sequence. 22. Arrangement for decrypting data packets in a wireless network, in which a processor unit is provided which is set up in such a way that the data packets comprise data blocks, the data packets can be counted using a first counter, the data blocks can be counted using a second counter, a cryptographic bit sequence can be determined by linking a counter composed of the first counter and the second counter with a key to a cryptographic algorithm for the data block, and - The data packets can be decrypted with this processor unit using the cryptographic bit sequence.