JP4981802B2 - Data encryption in communication networks - Google Patents

Description

  The present invention relates to network protocols. More particularly, the present invention relates to data encryption in communication networks.

  In a communication network, information is obscured using encryption so that a network node or an eavesdropper cannot easily determine information without secret information called a key. The cipher is an algorithm for performing encryption. A block cipher such as the next American Standard Encryption (AES) is a symmetric key cipher that encrypts data of a fixed-length block called “plaintext block” with an encryption key and generates an encrypted “ciphertext block”. It is possible to decrypt the ciphertext block using the encryption key and reproduce the plaintext block.

  When the data stream to be encrypted is longer than the block size, the block cipher uses an “operation mode” to encrypt the data stream. In one mode of operation called electronic codebook (ECB) mode, the stream is divided into a plurality of blocks, and each plaintext block is individually encrypted using an encryption key. In ECB mode, the same plaintext block in different parts of the stream is mapped to the same ciphertext block, so some patterns of the original data stream may not be obscured.

  In another mode of operation called cipher block chaining (CBC) mode, the stream is divided into blocks, and each plaintext block is based on the previous ciphertext block (using an exclusive OR operation) before being encrypted. )It is processed. In the CBC mode, each ciphertext block depends on all previous ciphertext blocks, which helps obfuscate the pattern of the original data stream.

  Since the first ciphertext block does not have the previous ciphertext block, it is processed based on the “initialization vector”. An initialization vector used in CBC mode block ciphers or other types of ciphers also provides some form of randomization. By using different initialization vectors for different data streams, it becomes more difficult to obtain information about the original data stream or encryption key from the encrypted stream. The initialization vector is used (with the encryption key) to decrypt the corresponding encrypted stream, and (unlike the encryption key) can be transmitted over the network with the corresponding encrypted stream without compromising security.

  In one aspect, in general, the invention features a communication method in a network. The method encapsulates content of a plurality of upper data units from an upper layer to generate a stream, a step of dividing the stream into a plurality of segments, and a step of individually encrypting at least some segments. The encrypted segment includes a plurality of encrypted blocks, and at least some of the encrypted blocks are encrypted based on one or more other encrypted blocks in the encrypted segment. And providing a lower data unit to a physical layer handling physical communication over a network, and at least some of the lower data units each include a plurality of encrypted segments.

Embodiments of this aspect of the invention may include one or more of the following features.
Each segment is divided into a plurality of data blocks, each encrypted segment is associated with overhead information, each subordinate data unit is associated overhead information, and the first cipher in the first subordinate data unit The first encrypted block in the encrypted segment includes an encryption key and a second encrypted block in the first encrypted segment, or at least partially in the first cipher Using an initialization vector derived from one or more of the portion of overhead information associated with the segmented segment and the portion of overhead information associated with the first subordinate data unit, Formed from data blocks.

The initialization vector is derived, at least in part, from overhead information associated with at least some functions other than encryption for receiving subordinate data units.
Providing the lower data units includes forming a series of physical layer blocks, each physical layer block including an encrypted segment and overhead information associated with the encrypted segment.

The overhead information associated with the encrypted segment includes one or more of a header and an integrity check sequence.
The integrity check sequence includes a cyclic redundancy check code that is calculated based on the header and the encrypted segment.

  The initialization vector is derived at least in part from both the portion of overhead information associated with the first encrypted segment and the portion of overhead information associated with the first subordinate data unit.

  The method further includes selecting a portion of overhead information associated with the first subordinate data unit based on which portion of the overhead information may be different for different subordinate data units.

The portion of overhead information associated with the subordinate data unit includes at least a portion of one or more of a source identifier and a destination identifier.
The method further includes selecting a portion of overhead information associated with the first encrypted segment based on which portion of the overhead information may be different for different segments.

  The portion of overhead information associated with the first encrypted segment identifies the sequence number associated with the first encrypted segment and the location of the first encrypted segment within the subordinate data unit. And at least a portion of one or more of the information and information identifying a location of a boundary between higher data units in the segment from which the first encrypted segment was generated.

Each encrypted segment can be retransmitted independently.
At least some segments are encoded using forward error correction.
The method further includes retransmitting a segment that has not been successfully received, including re-encrypting the segment with the new initialization vector.

The method further includes selecting a segment length to reduce padding associated with at least some of the segments.
The length selected is a multiple of the cipher block size used for cipher block chain mode encryption of the segment.

The length of the initialization vector is the same as the length of the encryption block size used for the encryption block chain mode encryption of the segment.
The upper layer includes a medium access control layer.

  In another aspect, in general, the invention features an apparatus for transmitting information over a network. The apparatus comprises a circuit configured to connect a signal to a communication medium and a network interface module connected to the circuit. The network interface module generates a stream by encapsulating the contents of a plurality of upper data units from an upper layer, divides the stream into a plurality of segments, individually encrypts at least some segments, and physically transmits them through the network. Includes circuitry configured to provide lower data units to a physical layer handling communications. The encrypted segment includes a plurality of encrypted blocks, at least some of the encrypted blocks are encrypted based on one or more other encrypted blocks in the encrypted segment; At least some of the subordinate data units each include a plurality of encrypted segments.

The many advantages of the present invention, some of which can be achieved only in some of the various aspects and embodiments of the present invention, are as follows:
Higher communication efficiency (eg, payload to overhead ratio) by deriving initialization vectors for segment encryption and decryption, at least in part, from overhead information associated with the segment or subordinate data units containing the segment Can be achieved). If the overhead information is related to at least some functions other than encryption for receiving the subordinate data unit, no additional overhead due to the initialization vector is added.

  After the receiving station receives overhead information for the subordinate data unit, the only other information necessary to derive the initialization vector for a given encrypted segment is the overhead information associated with that segment. By encrypting the segments independently, including deriving IV from the overhead information independent for each segment, then when an uncorrectable error is detected in the segment, it is re-encoded to decrypt the segment. All that needs to be transmitted is the portion of the subordinate data unit that contains the segment.

  As shown in FIG. 1, the network configuration 2 includes a communication medium 3 through which several communication stations 6 to 10 (for example, a computing device or an audiovisual device) communicate with each other. The communication medium 3 can include one or more types of physical communication media, such as, for example, coaxial cables, optical fibers, unshielded twisted pair cables, or power transmission lines. The network configuration 2 can also include a device such as a bridge or a repeater. Communication medium 3 can connect communication stations in network configuration 2 according to any of a variety of network topologies (eg, bus, tree, star, mesh, etc.).

  The communication stations communicate with each other according to a predetermined network architecture. Abstract objects that form multiple layers of a network architecture are sometimes referred to as communication protocols. The communication protocol provides the communication service with higher objects (application processing, ie higher layers, etc.) that are used to send and receive information. For example, in some network architectures, the lowest layer includes physical (PHY) layer and medium access control (MAC) layer communication protocols. The PHY layer performs conversion between data and a signal waveform transmitted through the communication medium 3. The MAC layer is a sublayer of the data link layer and provides an interface to the PHY layer, for example, according to the Open Systems Interconnection (OSI) network architecture standard.

  The communication stations 6 to 10 include respective network interface modules 12 to 16 that implement a communication protocol by hardware, software, or a combination of hardware and software for each station. These stations may use different specific communication protocols, but can still communicate with each other if the protocols are compatible. The communication protocol of the transmitting station transmits data in the form of data units to the peer communication protocol of the receiving station. At each station, data units are passed up and down between multiple layers of communication protocols (ie, a “protocol stack”). The communication protocol receives a service data unit (SDU) from a higher layer protocol, encapsulates the SDU (eg, as a header) using protocol control information (PCI), and is provided as an SDU to the lower layer Forming a protocol data unit (PDU). Thus, each lower layer provides services to the upper layer to ensure that the encapsulated SDU is delivered to the peer protocol.

  For example, the transmitting station's MAC layer protocol transmits a MAC protocol data unit (MPDU) to the receiving station's MAC layer protocol. The MPDU includes, in addition to the application layer payload, PCI and other overhead information related to the MAC layer and higher layer SDUs (eg, header information or tail cyclic redundancy check (CRC) code). The MAC layer provides the MPDU to the PHY layer as a PHY service data unit (PSDU) transported through the communication medium 3. The PHY protocol data unit (PPDU) represents a modulated signal waveform that represents the PSDU transmitted over the communication medium 3.

FIG. 2 shows an exemplary system interface and associated data units in a portion of the reference network architecture 50 that can be used by network configuration 2. This part may be implemented at each station. FIG. 2 illustrates a protocol adaptation layer (PAL) that includes one or more layers of a network architecture, namely, bridge / PAL _i 52, MAC 54, and physical layer (PHY) 56. The bridge / PAL _i 52, the MAC 54, and the physical layer (PHY) 56 are separated by an M1 interface 62 and a PS interface 64, respectively.

The upper interface H1 _i 58 represents the i-th host interface. One interface is supported for each protocol. The H1 _i interface 58 defines the boundary points of the i th host protocol data unit (H _i PDU) 68 and the i th protocol adaptation layer service data unit (PAL _i SDU) 69 for the upper layers of the network architecture 50. To do.

For each supported protocol, the corresponding bridge / PAL _i 52 may be implemented in part by host software and in part by firmware, hardware or both. The example architecture 50 supports IEEE 802.3 and isochronous stream protocols and provides access to dedicated protocols for other networks through the interface 60. Bridge / PAL _i 52 supports higher layer adaptation (HLA) functions, bridge functions, or both. Both HLA and bridging operations involve translation of host data packets containing PAL protocol data units (PAL _i PDUs) 70 into MAC service data units (MSDUs) 71, and conversely, PAL protocols in MAC service data units (MSDUs) 71. Supports translation into host data packets including data units (PAL _i PDUs) 70, and translation of host addresses from the H1 interface 58 to corresponding network interface 12-16 addresses (eg, MAC addresses) To do. HLA and bridging operations also support the determination of traffic class and QoS parameters in addition to the establishment of a stream harmonized with the MAC layer.

The M1 interface 62 is common to all protocol adaptation layers and defines the boundary between a given bridge / PAL _i 52 and the MAC layer 54. PAL protocol data units (PAL _i PDUs) 70 are passed down as MAC service data unit (MSDU) 71 from bridge / PAL _i 52 to MAC layer 54, and vice versa from MAC layer 54 to bridge / PAL _i 52 Passed to.

The medium access control (MAC) layer 54 processes the MAC service data unit (MSDU) 71 from the bridge / PAL _i 52 and delivers it to the physical layer 56 as a PHY service data unit (PSDU) 73 ( MPDU) 72 is generated. The processing of the MAC layer 54 includes, for example, service interface for PAL 52, network management, admission control, encryption, error control (ARQ), retransmission, escalation, framing, fragmentation / reassembly, packet encapsulation / decapsulation Channel access (contention free burst, management session, CSMA / CA, etc.), time stamp, multimedia clock synchronization, and contention free session.

  The physical layer signaling (PS) interface 64 separates the MAC layer 54 and the PHY 56, and the MAC protocol data unit (MPDU) 72 is connected to the PHY from the MAC layer 54 through the PS interface 64 as a PHY service data unit (PSDU) 73. 56 and vice versa from PHY 56 to MAC layer 54.

  The physical layer (PHY) 56 protocol provides various operations for transmitting a PHY protocol data unit (PPDU) signal 74. The PHY protocol data unit (PPDU) signal 74 includes symbols in which PSDU 73 data is modulated according to a modulation scheme. For example, in an orthogonal frequency division multiplexing (OFDM) modulation scheme over a shared communication medium such as a transmission line medium, PHY 56 is forward error correction (FEC) encoding, encryption, physical carrier sensing, frame control decoding, error detection, It is possible to provide information necessary for channel estimation and selection of a “tone map” of carrier frequencies used for OFDM communication.

Any of a variety of communication system architectures can be used to implement the portion of the network interface module that performs the conversion between data and signal waveforms transmitted over the communication medium. In OFDM modulation, data is transmitted in the form of OFDM “symbols”. Each symbol has a predetermined duration, ie symbol time T _s . Each symbol is generated by a superposition of N sinusoidal carrier waveforms that are orthogonal to each other and form an OFDM carrier. Each carrier has a peak frequency f _i and a phase φ _i measured from the start of the symbol. For each of these mutually orthogonal carriers, the total number of periods of the sinusoidal waveform is within the symbol time T _s . That is, each carrier frequency is an integer multiple of the frequency interval Δf = 1 / T _s . The phase φ _i and the amplitude A _i of the carrier waveform can be selected independently (according to the appropriate modulation scheme) without affecting the orthogonality of the resulting modulated waveform. The carrier occupies a frequency range of frequencies f _{1 to} f _N called OFDM bandwidth.

  With reference to FIG. 3, communication system 300 includes a transmitter 302 for transmitting a signal (eg, a series of OFDM symbols) to a receiver 306 over a communication medium 304. Both the transmitter 302 and the receiver 306 can be incorporated into the network interface module of each station. Communication medium 304 may represent a path from one device to another through a transmission line network.

  At transmitter 302, the module that implements the PHY layer receives the MPDU from the MAC layer. The MPDU is sent to the encoder module 320 to perform processes such as scrambling, error correction coding, and interleaving.

The encoded data is supplied to the mapping module 322. The mapping module 322 is a group of data bits (eg, 1, 2, 3, 4, 6 or the like) depending on the constellation used for the current symbol (eg, BPSK, QPSK, 8-QAM, 16-QAM constellation). 10 bits) and map the data values represented by those bits to the corresponding amplitudes of the in-phase component (I) and the quadrature component (Q) of the carrier waveform of the current symbol. Thus, each data value related to the corresponding complex number C _i = A _i exp (jφ _i ) whose real part corresponds to the I component of the carrier of the peak frequency f _i and whose imaginary part corresponds to the Q component is Arise. Alternatively, any suitable modulation scheme that associates data values with the modulated carrier waveform can be used.

In addition, the mapping module 322 is configured to transmit carrier frequencies f ₁ ,. . . , F _N to be used. For example, some carriers experiencing fading can be avoided and no information is transmitted on those carriers. Alternatively, the mapping module 322 uses coherent BPSK modulated with binary values from a pseudo-noise (PN) sequence for that carrier. For some carriers (eg, carrier i = 10) corresponding to a limited band (eg, amateur radio band) on the power radiable medium 304, no energy is transmitted on those carriers (eg, A ₁₀ = 0). The mapping module 322 also determines the type of modulation (ie, “tone”) used for each of the carriers according to the “tone map”. The tone map may be a default tone map or a customized tone map determined by the receiving station.

The inverse discrete Fourier transform (IDFT) module 324 is configured such that the mapping module 322 has peak frequencies f ₁ ,. . . , F _N is performed on a set of N complex numbers (some of which may be 0 for unused carriers) determined on N orthogonal carrier waveforms. Modulated carriers are combined by IDFT module 324 to form a discrete time symbol waveform S (n) (at sampling rate f _R ). This can be written as:

Here, the time index n advances from 1 to N, A _i is the amplitude, φ _i is the phase of the carrier with the peak frequency f _i = (i / N) f _R , and j = √ (−1) It is. In some embodiments, the discrete Fourier transform corresponds to a fast Fourier transform (FFT) where N is a power of two.

The post-processing module 326 combines a series of consecutive (possibly overlapping) symbols into a “symbol set” that can be transmitted as a continuous block through the communication medium 304. The post-processing module 326 prepends the preamble to a symbol set that can be used for automatic gain control (AGC) and symbol timing synchronization. To mitigate inter-symbol and inter-carrier interference (eg, due to defects in system 300, communication medium 304, or both), post-processing module 326 uses a cyclic prefix that is a duplicate of the last part of the symbol to It is possible to extend the symbol. The post-processing module 326 also applies a pulse shaping window to the subset of symbols in the symbol set (eg, using a raised cosine window or other type of pulse shaping window), overlays the subset of symbols, etc. It is possible to perform other functions.

  An analog front end (AFE) module 328 connects an analog signal including a time continuous (eg, low pass filtered) version of the symbol set to the communication medium 304. The effect of transmitting a time-continuous version of the waveform S (t) through the communication medium 304 can be expressed by convolution using a function g (τ; t) that represents the impulse response of the transmission through the communication medium. The communication medium 304 may add noise n (t), which may be random noise emitted by the jammer, narrowband noise, or both.

  At receiver 306, the module that implements the PHY layer receives signals from communication medium 304 and generates MPDUs for the MAC layer. The AFE module 330 works with an automatic gain control (AGC) module 332 and a time synchronization module 334 to provide sampled signal data and timing information to a discrete Fourier transform (DFT) module 336.

  After removing the cyclic prefix, the receiver 306 provides the sampled discrete time symbols to the DFT module 336 to represent a series of N numbers representing the encoded data values (by performing an N-point DFT). Extract complex numbers. Demodulator / decoder module 338 maps the complex number to the corresponding bit sequence and performs the appropriate bit decoding (including de-interleaving and descrambling).

  Any module of the communication system 300, including a transmitter 302 or receiver 306 module, can be implemented in hardware, software, or a combination of hardware and software.

  In some embodiments, MPDUs can be generated from a stream of MSDUs such that there is not necessarily a one-to-one correspondence between MSDUs and MPDUs. For example, in the MAC framing process, each of a series of MAC frames (or “subframes”) is generated from one or more MSDUs, and multiple MAC frames are concatenated into a stream of MAC frames. The MAC frame stream is then partitioned into multiple segments (eg, fixed size segments) that can be included in the MPDU.

Referring to FIG. 4, the MAC frame stream 100 includes a continuous stream of MAC frames that can vary in length. The segment 102 is formed from a part of the MAC frame stream 100. Depending on the relative sizes of the segment 102 and the MAC frame, the segment can include a portion of a MAC frame, multiple MAC frames, or both. Thus, a segment can include zero or more boundaries between MAC frames. For each segment, the MAC layer records the offset of the first MAC frame boundary within that segment. This boundary information is transmitted with the segment and used by the receiving station to distinguish the MAC frame from the received segment. Since the other MAC frame boundaries (if any) can be determined from the information of the previous MAC frame (eg, the length information of the MAC frame), the first MAC frame boundary in the segment is sufficient. When the receiving station needs to discard the segment from the previous MAC frame and continue reception with the next MAC frame, the receiving station can find the start of the next MAC frame by the MAC frame boundary information. Become. Each segment is associated with a segment sequence number (SSN). The SSN is initialized to 0 for the first segment of the MAC frame stream and incremented by 1 when a new segment is formed. SSN enables the receiving station to receive out-of-order segments and to detect duplicates.

  The end of the MAC frame stream 100 may not contain enough data to completely fill the segment 102 at a time when the segment is encapsulated into an MPDU (sent to the PHY layer as a PSDU). . In such a case, the MAC frame stream 100 can be padded with a pad portion 104 (eg, padded with zeros), thus forming a complete segment 102. Padding the MAC frame stream to form the last segment (eg, “Segment n” in FIG. 3) can be delayed until just before the segment is processed for delivery to the PHY layer, It is possible to allow time for the next MAC frame to be added to the MAC frame stream 100. A predetermined data value can be included at the beginning of the pad portion 104 to indicate the presence of padding in the remainder of the segment.

  The segment 102 is handled as an entity that is a target of reliable delivery service by the MAC layer and the PHY layer. Each segment 102 can be individually encrypted so that each segment can be decrypted at the receiving station without requiring any of the other segments. For example, a CBC mode block cipher (eg, a 128-bit AES cipher in CBC mode) converts data of the MAC frame stream 100 into a data block (ie, “128 bits, ie, 16 bytes”) of a given size (ie, “ It can be used by dividing it into plaintext blocks "). To eliminate the need to pad the last data block of the segment, the segment size can be selected to be a multiple of the data block size. Thus, each encrypted segment 106 includes a predetermined number of encrypted blocks (ie, “ciphertext blocks”).

  The MAC layer transmits each encrypted segment 106 within the PHY block (PB) 108 of the MPDU 110. The PB body (PBB) field 114 of the PB 108 carries the encrypted segment 106 as the payload of the PB 108. Other fields of the PB 108 carry overhead information (eg, information used by the PHY layer to transmit the encrypted segment 106). The PB header 116 includes, for example, fields for the SSN and the first MAC frame boundary offset (if any) associated with that segment. The PB header 116 can also include information indicating other characteristics of the segment, such as the type of stream to which the segment belongs (for example, a data stream or a management stream). A PB check sequence (PBCS) 118 is used to check the integrity of the PB 108 at the receiving station. The PBCS is a CRC code calculated for the PBB 114 and the PB header 116, for example.

  Each segment 102 (and encrypted segment 106) corresponds to a different PB 108 (or “FEC block”) that can be retransmitted independently. Because FEC encoding allows the PHY layer to detect errors based on PHY blocks, it is possible to retransmit segments 102 with errors without requiring retransmission of segments 102 without errors. is there.

The size of the segment 102 can be selected to provide a trade-off between high efficiency and low delay time. For example, the segment can be large enough so that the overhead information associated with segment 102 (eg, PB header 116 and PBCS 118) is small (eg, a small overhead to payload ratio) compared to the size of segment 102. is there. The segment can be small enough to isolate the effect of the error on a small range of data around the error so that the delay time for retransmitting the information is short. Also, the small size can reduce the potential size of the padding portion 104 of the final PB 108. An example of such a trade-off with a 16-byte data block, a 4-byte PB header 116 and a 4-byte PBCS 118 is 512 bytes, which results in a 520-byte PB 108.

  The MPDU 110 also includes an MPDU header 120 (ie, a “frame control” portion) that precedes a series of PBs 108. The MPDU header 120 includes overhead information associated with the transmission of the MPDU 110, information associated with all PBs 108 of the MPDU 110, or both. The MPDU 110 is passed to the PHY layer, modulated on the PPDU signal, and transmitted to the receiving station. The information contained in the MPDU header 120 and the PB header 116 can be used by the receiving station for reassembly of upper layer data units such as the stream to which the segment 102 belongs.

  Another aspect of the process of encrypting segment 102 to generate encrypted segment 106 is the selection of an initialization vector (IV) that is used to initialize the encryption process. For example, in CBC mode cipher, a given encrypted block in encrypted segment 106 replaces the corresponding data block in segment 102 with the preceding encrypted block or (first formed For encrypted blocks, it is formed by combining (eg, using an exclusive-or operation) with the IV associated with segment 102. The combined block is then encrypted using the encryption key.

  In order to properly decrypt the encrypted segment 106, both the encryption key and IV need to be known at the receiving station. A set of shared secret encryption keys can be known to both the transmitting station and the receiving station (eg, after distribution by a secure protocol), and can be a field in the MPDU header 120 (“Encryption Key Selection” (EKS)). Field) can specify which encryption key is used to decrypt the encrypted segment 106 of the corresponding MPDU 110. The IV does not necessarily have to be kept secret like an encryption key. However, using the same or highly predictable IV with the same encryption key may increase vulnerability to certain cryptographic attacks. The IV used to encrypt a given encrypted segment 106 can be transmitted with the segment (eg, via the PB header 116). However, the added overhead (eg, 16 bytes) is significant compared to the segment size (eg, 512 bytes) and may reduce efficiency.

  One approach to reduce the overhead in IV transmission is to encrypt the entire MPDU payload (multiple PBs), or the entire MAC frame, with a long chain using CBC mode encryption, which includes a single IV Only necessary. However, in this case, if any part of the chain is lost or corrupted, CBC mode encryption for subsequent encrypted blocks will depend on that lost part, so the previous data will be lost from that point in the chain. Is called.

  Another approach to reduce overhead in the transmission of IVs is to send new IVs less frequently, and then, according to a predetermined approach (eg, increment and transform with a known hash function), In response to IV, generate IV for other PB. In this case, however, when any of the new IVs are lost, the data encrypted using the IVs that depend on the lost IVs are lost.

  Another approach to reduce overhead in transmitting an IV is to receive MPDU 110 that includes overhead information associated with segment 102 (eg, PB header 116), overhead information associated with MPDU 110 (eg, MPDU header 120), or both. To derive IV from the overhead information already associated with at least some functions other than encryption. In an exemplary embodiment, the IV for an encrypted segment 106 in a given PBB field 114 is the corresponding field from the PB header 116, the field from the MPDU header 120, and the segment 106 (and the MPDU 110). It is obtained by concatenating the “segment count” indicating the relative position of the corresponding PB 108). The segment count is a value that can be determined at the receiving station and need not be transmitted or represented by any overhead information in the MPDU 110. The receiving station can simply increment the segment count for each segment received in the MPDU.

  Change from multiple fields that can be used to supply a portion of the IV from one MPDU 110 to the next MPDU or from one PB 108 to the next PB to provide a more unpredictable IV It is possible to select a field that is more likely to do. One MPDU 110 in all IVs can be selected by selecting multiple fields (or portions of fields) that may change even if any of the multiple fields may remain the same. Or the possibility of the PB 108 to the next MPDU or PB remaining the same is reduced. In this example, the IV for consecutive encrypted segments 106 will not be the same because the segment count increments from one PB 108 to the next PB in a given MPDU 110.

  Examples of selectable MPDU header 120 fields that may be included in the IV so that they may be different for different MPDUs are source address, destination address, link identifier, EKS, mooring PB, bit load estimate, tone map Index, MPDU count and burst count. Using the source and destination addresses ensures that the IV is different for each source / destination station pair that communicates. In other directions, the source is the destination and the destination is the source, so the IV is different in each direction. The link identifier identifies one of a plurality of possible streams from the source to the destination. The EKS used by the receiver to determine which encryption key to use may vary depending on various other factors such as the logical network to which the station belongs. The mooring PB represents the remaining amount in the buffer of the transmitted PB and is usually different for different MPDUs. The bit load estimate is based on the data rate associated with a given tone map. The tone map index changes when a different tone map is used. The MPDU count changes for successive MPDUs. The burst count is counted down for a burst of MPDUs to be transmitted (eg, 3, 2, 1, 0). In addition, the IV can include a test sequence for the MPDU header 120. This check sequence is computed as a function of all other fields in the MPDU header and acts as a high likelihood hash value that changes when one or more of the other fields change.

Examples of selectable PB header 116 fields that may be included in the IV so that they may be different for different PBs are SSN, MAC frame boundary offset, and MAC frame boundary flag. The SSN increments from one PB 108 to the next PB as the segment count does, but the SSN must always return to 0 (or 1 other starting value) at the start of the MPDU 110 as the segment count does There is no. Since the SSN also increments across the MPDU boundary, the SSN is not repeated until it has made one round beyond its maximum value (eg, N _max = 65,535 for a 16-bit SSN). Until the SSN repeats (after one round), at least some bits change in the changing field (for example, the segment may not be the same position in the MPDU as the last segment with the same SSN) The count may be different), or the likelihood that a new encryption key will be used is high. Any two segments within N _max +1 of each other do not have the same IV.

  The MAC frame boundary flag indicates whether one or more boundaries exist between two MAC frames in the PB. If more than one boundary exists, the MAC frame boundary offset indicates where the first boundary occurs in the PB. If the MAC frame size changes or is not a multiple of the segment size, these fields may change.

  The combination of fields used in IV provides an IV with a low probability of repetition for a given cryptographic key. This cryptographic key can still provide an acceptable level of protection from cryptographic attacks.

  After the MPDU 110 is received at the receiving station, the PBCS 118 of each PB 108 is examined and a good PB is decoded. The PB 108 containing an uncorrectable error is reported to the transmitting station by an acknowledgment signal and uses the current encryption key and the new IV derived from the new overhead information of the MPDU in which the PB is being transmitted. Encrypted again and retransmitted.

Network configuration diagram. Reference network architecture diagram. 1 is a block diagram of a communication system. The figure of a format of MPDU.

Claims (18)

In the communication method in the network,
A stream generation step of encapsulating the contents of a plurality of upper data units from an upper layer and generating a stream;
A stream dividing step of dividing the stream into a plurality of segments , each segment being divided into a plurality of data blocks, each segment being associated with overhead information ;
A segmented encryption step of encrypting individually at least some segments, the first encrypted segment saw including a plurality of encrypted blocks, block encrypted and the plurality of first The first encrypted block is associated with a first subordinate data unit formed from the first data block using an encryption key and an initialization vector, and is initialized. A vector is derived from a portion of segment overhead information associated at least in part with the first encrypted segment and a portion of overhead information associated with the first subordinate data unit ;
A subordinate data unit supplying step of supplying a subordinate data unit including a first subordinate data unit to a physical layer handling physical communication through a network, wherein at least some of the subordinate data units include a plurality of encrypted segments. A method comprising each of the steps . Each subordinate data unit is associated with data unit overhead information, and the plurality of encrypted blocks further comprises:
And encryption key, first the first second cipher in the encrypted segments associated with the first sub data unit formed from the second data block using the encrypted block including reduction block, method according to claim 1. 3. The method of claim 2, wherein the initialization vector is derived at least in part from data unit overhead information associated with at least some functions other than encryption for receiving subordinate data units. Lower data unit supplying step, claim and forming a series of physical layer blocks, each physical layer block and contain overhead information associated with the encrypted segments and the encrypted segments, one The method described in 1.   The method of claim 4, wherein the overhead information associated with the encrypted segment includes one or more of a header and an integrity check sequence.   6. The method of claim 5, wherein the integrity check sequence includes a cyclic redundancy check code that is calculated based on the header and the encrypted segment. 2. The method of claim 1 , comprising selecting a portion of overhead information associated with a first subordinate data unit based on which portions of the overhead information may have different possibilities for different subordinate data units. .   The method of claim 7, wherein the portion of overhead information associated with the subordinate data unit includes at least a portion of one or more of a source identifier and a destination identifier. The method of claim 1 , comprising selecting a portion of overhead information associated with a first encrypted segment based on which portions of the overhead information have different possibilities for different segments. . The overhead information portion associated with the first encrypted segment is:
A sequence number associated with the first encrypted segment;
Information identifying the location of the first encrypted segment in the subordinate data unit;
The method of claim 9, wherein the first encrypted segment includes at least a portion of one or more of information identifying a location of a boundary between higher data units in the generated segment.   The method of claim 1, wherein each encrypted segment is independently retransmittable.   The method of claim 11, wherein at least some of the segments are encoded using forward error correction.   12. The method of claim 11, comprising retransmitting a segment that has not been successfully received, including re-encrypting the segment with a new initialization vector.   2. The method of claim 1, comprising selecting a segment length to reduce padding associated with at least some segments.   15. The method of claim 14, wherein the selected length is a multiple of the cipher block size used for cipher block chained mode encryption of the segment.   The method of claim 1, wherein the length of the initialization vector is the same as the length of the cipher block size used for cipher block chain mode encryption of the segment.   The method of claim 1, wherein the upper layer comprises a media access control layer. An apparatus for transmitting information through a network,
A circuit configured to connect a signal to a communication medium;
A network interface module connected to the circuit,
Network interface module
A step Ru generate a stream by encapsulating content from a plurality of upper data units from the higher layer,
Dividing the stream into a plurality of segments , each segment being divided into a plurality of data blocks, each segment being associated with overhead information ;
Individually encrypting at least some of the segments , wherein the first encrypted segment includes a plurality of encrypted blocks, the plurality of encrypted blocks being first encrypted. The first encrypted block is associated with a first subordinate data unit formed from the first data block using an encryption key and an initialization vector, and the initialization vector is at least Derived in part from a portion of segment overhead information associated with the first encrypted segment and a portion of overhead information associated with the first subordinate data unit ;
Step several lower data units even without least a step of supplying the lower data units each including a plurality of encrypted segments comprising a first lower data units to the physical layer dealing with physical communication over the network And a circuit comprising a circuit for performing the operation .

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