Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04K—SECRET COMMUNICATION; JAMMING OF COMMUNICATION
  • H04K1/00—Secret communication
  • H04K1/06—Secret communication by transmitting the information or elements thereof at unnatural speeds or in jumbled order or backwards

Definitions

• the present invention relates to the encryption of discrete signals, e.g. on the encryption of voice information or the corresponding decryption.
• the encrypted signals must not cause any damage when listening without decrypting the listening system.
• the encrypted signals should therefore be encrypted in such a way that they do not produce any crackling, crackling or other extreme dynamic jumps when played without decryption. While it is often sufficient to encrypt the quality of the unauthorized reproduction when encrypting music data, ' with speech content it is particularly required that the reproduction quality of the encrypted data with unauthorized use does not make the speech information understandable, which can be interviews, reports, etc., for example allow more.
• the object of the present invention is to provide a method and a device for encrypting a discrete signal as well as a method and a device for corresponding decryption, so that the encryption on the one hand is as secure as possible and on the other hand does not produce any errors in unauthorized processing and with previous encodings is tolerated.
• the present invention is based on the knowledge that a very high level of security of the encryption can be achieved by introducing a temporal discontinuity, and that the occurrence of errors in the case of unauthorized processing of such encrypted signals can thereby be prevented and the compatibility with standard encodings can be ensured in that the change in the temporal order after coding the discrete signal, ie with respect to coded data blocks into which an encoder encodes the discrete signal, is carried out. In this way, on the one hand, it is prevented that a decoder, which receives the encrypted signal, does not get into undefined states, since during the encryption the temporal discontinuity is generated in units of coded data blocks.
• the successive samples of a discrete signal are divided into successive time blocks, which are then encoded in coded data blocks with a predetermined order.
• the predetermined sequence of the coded data blocks is then changed in accordance with a predetermined exchange rule.
• the order of the coded data blocks of an encrypted signal which corresponds to a discrete signal, which consists of successive samples, in encrypted form, is changed according to a predetermined exchange rule or an inverse exchange rule, whereupon the encoded data blocks are changed Order are decoded into successive time blocks with a predetermined order.
• the successive samples of the discrete signal are generated from the successive time blocks.
• the change in the predetermined sequence of the encoded data blocks during encryption is achieved by permuting a predetermined number of successive data blocks of the encoded data blocks, a permutation vector being generated as a swapping rule for this purpose.
• the permutation can be carried out with respect to successive groups of coded data blocks of the same size or length.
• a different permutation vector can be generated and used for each permutation group.
• the generation of the permutation vectors takes place in the decoding in a predetermined way, with a correct decryption there by ensuring that corresponding inverse permutation vectors are generated and used in the decryption for the back permutation of the groups of coded data blocks.
• FIG. 1 shows a block diagram of an encryption device according to an exemplary embodiment of the present invention
• FIG. 2 shows a block diagram of a decryption device according to an exemplary embodiment of the present invention
• Fig. 3 is a schematic sketch showing an exemplary embodiment of encryption.
• Fig. 4 is a schematic sketch showing an exemplary embodiment of a decryption.
• 1 shows an encryption device according to an embodiment of the present invention, which converts a discrete time signal or an audio signal into coded data blocks in encrypted form.
• 1 essentially comprises a psychoacoustic encoder 10 which receives the time signal and converts it into coded data blocks, and a device 12 for changing the order of the coded data blocks.
• the psychoacoustic encoder 10 comprises a device 14 for dividing the successive discrete samples which make up the time signal into time blocks and a device 16 for coding the time blocks into coded data blocks.
• the device 12 for changing the sequence comprises a device 18 for generating a permutation vector, a writing device 20, a first buffer 22, a second buffer 24 and a readout device 26.
• An input of the writing device 20 is connected to an output of the psychoacoustic encoder 10 or Device 16 connected for coding, while two outputs of the same are each connected to an input of the first and second buffers 22 and 24.
• An output of the device 18 for generating a permutation vector is connected to an input of the readout device 26 in order to output a permutation vector thereon, the readout device having two further inputs which are connected to the outputs of the intermediate memories 22 and 24.
• the read-out device 26 is connected at an output to an output buffer 28 in order to output coded data blocks to it in encrypted form.
• the time signal is a discrete audio signal that consists of successive samples.
• the psychoacoustic encoder 10 is based, for example, on an encoding method of the AAC standard.
• the device 14 divides the successive samples, for example, into time blocks with a number of successive samples which is equal to a power of 2. To handle aliasing effects, provision can be made for a division into mutually overlapping time blocks, so that each sample value has two time intervals. block is allocated, as is the case with AAC coding, for example.
• the device 16 for coding the time blocks into coded data blocks receives the time blocks from the device 14 in chronological order and then carries out the coding thereof.
• the coding of a time block can be carried out either individually or in isolation, time block by time block, or depending on previous and subsequent time blocks, in order, for example, to use psychoacoustic models, e.g. the temporal and spectral concealment to be taken into account.
• the device 16 for encoding the time blocks outputs the encoded data blocks to the writing device 20 in a predetermined sequence which is dependent on the encoding method.
• the data blocks can either all have the same length or different lengths, e.g. in the event that the data blocks have an MPEG2 / 4 AAC compliant structure.
• the writer 20 receives the encoded data blocks and successively writes the encoded data blocks into a current one of the buffers 22 and 24, acting together as a removable buffer, as will be described below.
• the size of the buffers 22 and 24 is sufficiently large to store N coded data blocks, where N is an integer greater than 1 (N> 1).
• the writing device 20 writes the current one of the memories 22 and 24 in the order in which the coded data blocks are transmitted by the device 16 until there are N coded data blocks in the current one of the buffers 22 and 24.
• the read-out device 26 reads out the buffer 22 and 24 just filled, while the write device 20 reads the other of the two buffers 22 and 24 with the coded data blocks from the Device 16 describes in the order of their receipt.
• the read-out device 26 reads out the buffer memory 22 or 24, which was last completely described, in a different order than the same was described.
• the read-out device 26 reads out the respective intermediate memory 22 or 24 in a permuted sequence, which is determined by a permutation vector of size N, which is generated and supplied by the device 18 for generating a permutation vector, as will be described below .
• a permutation vector of size N which is generated and supplied by the device 18 for generating a permutation vector, as will be described below .
• the coded data blocks read out in permuted order together form a permutation group of coded data blocks which the readout device 26 outputs to the output buffer 28, to which, for example, a computer interface (not shown) is connected.
• the device 18 generates the permutation vector of size N, which defines the exchange rule, on the basis of which the coded data blocks of a permutation group are permuted, for each permutation group.
• the generation of a permutation vector is based on N pseudo random numbers that are generated by the pseudo random number generator 30.
• the pseudo-random number generator 30 generates N pseudo-random numbers in succession for the generation of each permutation vector of length N and outputs them to the sorter 34, the counter 32 incrementing a counter value when each pseudo-random number is output and outputting it to the reorderer 36, the counter 32 having a value starts from 0 to output a value of 1 for the first pseudorandom number.
• the pseudo-random numbers that are output by the pseudo-random number generator 30 are numbered in parallel with the generation or provided with indices in the order in which they were generated.
• the pseudo-random numbers generated by the pseudo-random number generator 30 together form a random number vector or a random number array of N pseudo-random numbers, while the numbers generated by the counter 32 form an index vector or an index array which consists of numbers from 1 to N.
• the sorter 34 receives the random number vector and sorts it using a suitable sorting method, for example in increasing order.
• the sorter 34 is coupled to the reorder 36 to allow the reorder 36 to reorder the index vector received from the counter 32 in parallel with the sorting of the random number vector.
• the rearranged or permuted index array generated by the reorderer 36 represents the swapping rule for the N coded data blocks that are read next by the readout device and is output by the reorderer 36 as a permutation vector to the readout device 26, which is the same , as described above, used to define the readout order with respect to the corresponding buffer 22 or 24.
• the write device 20 and the read-out device 26 change to the respective one other buffers 22 and 24, respectively, the reading process being carried out with respect to the new coded data blocks written in the change buffer, which are then output to the output buffer in permuted order.
• the output buffer in permuted order.
• a decryption device according to an exemplary embodiment of the present invention is explained below with reference to FIG. 2.
• the decryption device of FIG. 2 is provided in order to transmit the encoded data blocks of the encryption device which are output in encrypted form. 1 again in a time signal, depending on the coding used in a lossy or lossless manner.
• the device of FIG. 2 comprises a device 38 for changing the order of the received coded data blocks, which represent the encrypted signal, and a decoder 40, which is connected to the device 38 and decodes the coded data blocks.
• the device 38 has an arrangement similar to the device 12 of the encryption device of FIG. 1, and consists of a writing device 42, a buffer 1 44, a buffer 2 46, a read-out device 48 and a device 50 for generating an inverse permutation vector 1, which has a structure similar to the device 18 of the encryption device of FIG. 1 and is therefore not shown in more detail in FIG. 2 for reasons of clarity.
• the writing device 42 receives the coded data blocks, which are present in the encrypted form, at an input and is connected to an input of the buffer memory 44 or of the buffer memory 46 at two outputs.
• the readout device comprises three inputs, one of which is connected to an output of the device 50 for generating an inverse permutation vector and the other two are each connected to an output of the buffer memory 44 and 46, respectively.
• An output of the readout device 48 is connected to the decoder 40 to transmit the decoded data blocks in a predetermined order, i.e. in the order intended for decoding according to the respective coding method.
• the decoder 40 comprises a device 52 for decoding the coded data blocks which are output by the read-out device 48, and a device 54 following the device 52 for forming the successive samples, the device 54 receiving the time signal. outputs for example to a digital / analog converter (not shown) or the like.
• the writer 42 receives the encoded data blocks, which are in encrypted form, and outputs them in the order in which they are transmitted to a current one of the buffers 44 and 46 which, like the encryption device of Fig. 1, cooperate as a removable buffer. While the writing device 42 fills one of the two buffers 44 and 46 in succession with N coded data blocks, the reading device 48 reads out the other buffer. While one buffer is being filled with the coded data blocks in the transmission order, the reading of the other buffer is carried out in permuted order, which depends on the inverse permutation vector generated by the device 50.
• An inverse permutation vector means here that the interchanging rule generated by the inverse permutation vector reverses the interchanges that were made by the decryption device of FIG. 1 on a respective interchanging or permutation group of N-coded data blocks.
• the device 50 generates the inverse permutation vectors per readout, for example using the same arrangement of devices as is shown for the device 18 in FIG. 1, the device 50, however, from the permutation vector as generated by the device 18 by a suitable device generates an inverse permutation vector, for example by applying the interchange rule defined by the permutation vector to a vector as it is output by the counter (see 32 in FIG. 1), ie a vector of ordered numbers from 1 to N.
• the N coded data blocks read out in a permuted order by the read-out device 48 are fed to the device 52 for decoding the coded data blocks, the same now being present in the predetermined order which is necessary for decoding the coded data blocks in accordance with the coding method on which the decoder 44 is based to get the correct time signal.
• the read-out device 48 After the read-out device 48 has read out the respective intermediate store or the write device 42 has completely filled the other intermediate store, the read-out device reads out the intermediate store which has just been filled by the write device 42, while the write device 42 describes the intermediate store which has been read out by the read-out device 48 ,
• the device 52 decodes the encoded data blocks and outputs time blocks in a predetermined order.
• the device 54 receives the time blocks and uses them to form the successive samples from which the time signal is made, and outputs them, for example, to an analog / digital converter (not shown).
• FIGS. 3 and 4 After exemplary embodiments for an encryption or decryption device have been described in the foregoing, an explicit embodiment is described below with reference to FIGS. 3 and 4, in which a discrete signal is encrypted by the device of FIG. 1 into an encrypted signal and the latter is decrypted by the device of FIG. 2, with additional reference being made to FIGS. 1 and 2.
• each sample can be located in one or more of the time blocks 66, or the time blocks can overlap one another in order to eliminate aliasing artifacts.
• each encoded data block 70 can have an individually different length or size, as illustrated by the different sizes of the blocks.
• a state is shown at 72 as it arises for the successive coded data blocks 70 during the encryption in the encryption device of FIG. 1.
• state 72 as in the following states in FIG. 3, in particular the contents of the buffer store 1 (22 in FIG. 1), the buffer store 2 (24 in FIG. 1) and the output buffer (28 in FIG. 1 ) for the respective state.
• the state is shown for the exemplary case that the exchange group size is set to 5 during encryption or decryption.
• the state shown at 72 corresponds to the state as it arises in the device of FIG. 1 after the first five A-Es have been written by the data blocks 70 at 68 into the active or current buffer, in this case buffer 1 have been.
• the values in the buffer 2 and the output buffer may depend on previous coded data blocks, and are therefore shown with dashes. As can be seen, the coded data blocks A-E have been stored in the buffer 1 in their predetermined sequence.
• the state is shown as it results after five further coded data blocks.
• the 5 further coded data blocks F - J have been written into the buffer 2, while the coded data blocks stored in the buffer 1 have been read out into the output buffer.
• the permutation vector, as indicated at 76, has been used for reading out the coded data blocks stored in the buffer 1. (4,3,5,2,1).
• the permutation vector 76 assigns each coded data block in the buffer 1 a number between 1 to 5 or N which indicates the readout order or the position at which this coded data block is to be written into the output buffer, so that in the Output buffer the encoded data blocks AE are in the order EDBAC.
• the state is shown after a further 5 coded data blocks.
• the 5 subsequent coded data blocks K-0 have in turn been written into the buffer 1, while in the meantime the buffer 2 has been read out into the output buffer by means of a permutation vector 80 (5,1,3,2,4) is where the encoded data blocks result in the order GIHJF.
• the stream or the sequence of coded data blocks is shown in encrypted form, as they are input into or output from the output buffer 28.
• the coded data blocks are scrambled compared to the predetermined order in which they are usually output by the coding on which the encoder 10 is based, which is why in the event that the audio data carries speech information this speech information is incomprehensible when decoded without decryption according to the present invention. Nevertheless, decoding without decryption prevents the decoder from entering invalid states, since the temporal discontinuity is defined in units of encoded data blocks.
• IMDCT inverse modified discrete cosine transform
• the signal 82 is received by a decoder or a decryption device according to FIG. with a corresponding inverse exchange of the input data, decrypted, then the data blocks or the data frames are again in the correct order in the buffer and the subsequent decoding can be carried out in accordance with the standard.
• This decryption process is explained in more detail with reference to FIG. 4 for the explicit embodiment of FIG. 3.
• FIG. 4 shows at 84 an example of a sequence of coded data blocks in encrypted form, which in this case corresponds to that of FIG. 3 at 82.
• Shown at 86 is a state that occurs in the decryption device of FIG. 2 after it has received the first five of the encoded data blocks of 84.
• the content of the buffer store 1 (44 in FIG. 2)
• the content of the buffer store 2 (46 in FIG. 2)
• the sequence of coded ones Blocks of data output from device 38 to encoder 40 are shown.
• the decoded data blocks are placed in the current buffer, in this case buffer 1, in the order in which they are transmitted.
• the state is shown at 88 as it arises after five further coded data blocks FGHIJ.
• the next five coded data blocks have been written into the buffer 2, while by means of an inverse permutation vector 90 the coded data blocks EDBAC are read out from the buffer 1 in order to be transmitted to the decoder 40 in the order ABCDE, whereby the inverse permutation vector results from the permutation vector 76 of FIG. 3, which related to the same permutation group, by applying the latter as a swapping rule to a vector (1,2,3,4,5).
• the state is shown at 92 as it results from the stream of coded data blocks 84 after reading out a further five coded data blocks.
• the buffer 1 has again been filled with the following coded data blocks K - 0, while the coded data blocks GHIJF in the buffer 2 have been read out to the decoder and output in a permuted sequence or inversely permuted sequence FGHIJ.
• the back permutation is based on the inverse permutation vector 94, which results from the permutation vector 80 of FIG. 3 by applying the latter to a vector (1,2,3,4,5).
• the stream of successive encoded data blocks is shown as it is fed to the decoder.
• the order in which the encoded data blocks have been output by the encoder of the encryption device is restored, ie ABCDEFGHIJKLMN ..., so that the decoding can be carried out in accordance with the standards.
• the description provided above with reference to FIGS. 1 to 4 related to encryption which is based on the exchange of data blocks of the time signal within a block group or exchange group.
• the block swapping in the time domain destroys the temporal modulation of a speech signal in such a way that intelligibility is considerably reduced in the case of a speech signal.
• An advantage of the above exemplary embodiments is that although a psychoacoustic compression method is used in the preceding exemplary embodiments to encode the time signal, the assumptions on which this psychoacoustic compression method is based, such as, for example, about the temporal and spectral concealment, remain valid since the temporal discontinuity is only is generated after compression, ie the chronological order of the already encoded data frames is exchanged.
• the exemplary embodiments described above can basically be used for all encoded data streams which are based on a sequential sequence of data frames which are self-contained and overlap after coding.
• the speech incomprehensibility of the encrypted signal can be improved in that the psychoacoustic encoder 10 or a device between the same and the device for changing the order a frequency range scrambling according to the in the Introduction to the mentioned patent application W099 / 51279.
• the present invention both in hardware, such as, for example, as an ASIC, an integrated circuit or the like, and in software, such as, for example, as a PC Software that can be implemented.
• the present invention has been applied to the encryption of audio ten or voice signals has been described, the present invention is generally applicable to all areas in which discrete signals are used and where appropriate coding thereof takes place, such as in image and video processing or data transmission in general.
• the coding preceding the generation of the temporal discontinuity in the encryption is not limited to a psychoacoustic coding.
• JPEG encoding is also possible for image or video data.
• the present invention can be implemented with all coding methods that subdivide successive discrete samples into time blocks and code them into coded data blocks or frames or directly code existing time blocks.
• the exact implementation of the device for generating a permutation vector can also be implemented differently, such as e.g. especially with regard to the length of the exchange group N or the number and size of the buffers used.
• the device for generating a permutation vector can be implemented differently than described above.
• the permutation vector could be the same for all exchange groups, in which case the inverse permutation vector would also be fixed.
• the principle of permuting successive exchange groups used in the previous exemplary embodiments can be deviated from, and that the order change can also be carried out in other ways, such as e.g. by changing the order with respect to the entire coded data blocks, in which case it would be necessary to temporarily store all the coded data blocks before changing the order in the encryption and to store the entire coded data blocks before changing the order in the decryption.

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