Distributed energy access intelligent power grid platform data encryption transmission method and system

Abstract

The invention discloses a distributed energy access intelligent power grid platform data encryption transmission method and system, and relates to the technical field of data encryption, and the method comprises the steps: encrypting plaintext data through a DES algorithm; encrypting the DES subkey for 16 times by using the public key through an RSA (Rivest, Shamir and Adleman) algorithm; decrypting the DES subkey for 16 times by using the private key through an RSA algorithm; and decrypting to obtain the plaintext of the sender. The distributed energy access intelligent power grid platform data encryption transmission method provided by the invention is based on the characteristics of the RSA algorithm and is improved on the basis of the original two moduli, and by utilizing the direct relevance between the length of a large prime number and the security in the RSA algorithm, the calculation process is kept unchanged on the basis of the increase of the moduli, namely, the length of the large prime number is increased, and the security of the large prime number is improved. And the generation of the large prime number is improved, so that the security of the algorithm is greatly improved.

Description

Technical Field

[0001] The present invention relates to the field of data encryption technology, and in particular to a data encryption transmission method and system for a smart grid platform with distributed energy access. Background Art

[0002] The development of smart grid is inseparable from distributed energy. As an important supplement to smart grid, distributed energy plays an important role in energy renewable and small-scale power generation. When user data circulates and is shared among distributed energy sources, the privacy of users becomes a difficult problem. Smart grid integrates computer technology and automatic control technology, and can remotely control equipment for automatic monitoring, locate abnormal points in the first time, complete self-repair, and greatly improve the production efficiency of the power system. However, smart grid also faces data security threats, including false data injection attacks, personal privacy data attacks and other user-side attacks. Data attacks are more destructive. In the process of monitoring data sharing and transmission, not only personal privacy will be leaked, but also core data will be tampered, resulting in misjudgment and even safety accidents. Therefore, the present invention adopts RSA+DES hybrid encryption method to encrypt power grid platform data to improve the security of data transmission. Summary of the invention

[0003] In view of the above-mentioned problems, the present invention is proposed.

[0004] Therefore, the technical problem solved by the present invention is that the existing smart grid data transmission encryption method has the problems of insufficient encryption strength, low data transmission efficiency, susceptibility to false data injection attacks and personal privacy leakage. A single encryption algorithm (such as DES or RSA) is easy to be cracked when the key length is short, especially in the face of complex attacks, and security is difficult to guarantee. At the same time, when the traditional RSA algorithm is used for data encryption, due to the complexity of the key generation and encryption process, it is inefficient when processing large amounts of data and the transmission speed is slow. In addition, the existing system cannot effectively prevent false data injection during data sharing and transmission, which can easily lead to misjudgment or even safety accidents in power grid operation. When user data is transmitted in a smart grid platform connected to distributed energy, the security of private data cannot be fully guaranteed.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions: a method for encrypting and transmitting data on a smart grid platform for access to distributed energy, comprising:

[0006] Encrypt plaintext data using the DES algorithm;

[0007] The DES subkey is encrypted 16 times with the public key through the RSA algorithm;

[0008] Decrypt the DES subkey 16 times using the private key through the RSA algorithm;

[0009] Decrypt to get the sender's plaintext.

[0010] As a preferred solution of the data encryption transmission method of the smart grid platform for distributed energy access described in the present invention, wherein: the encrypted plaintext data includes replacing the IP of the encrypted data with the DES algorithm, and the encrypted data units are L0 and R0 respectively;

[0011] Using the iterative formula to calculate 16 times, we can get L 16 and R 16 ;

[0012] For L 16 and R 16 Perform IP inverse permutation to obtain the ciphertext M.

[0013] As a preferred solution of the data encryption transmission method for the smart grid platform of distributed energy access described in the present invention, wherein: the IP inverse substitution is expressed as,

[0014] F DES =P'-1×T 16 ×T 15 ×…×T1×P'

[0015] Wherein, P' represents the initial transformation, P'-1 represents the inverter of P', satisfying IP'×IP'-1=1, and T represents the number of encoding operation rounds.

[0016] As a preferred solution of the data encryption transmission method for the smart grid platform with distributed energy access described in the present invention, wherein: the 16-time encryption of the DES subkey includes key generation;

[0017] Randomly select four arbitrary large prime numbers p, q, r and s, and calculate n = pqrs and Euler function

[0018] Seek a satisfaction A positive integer e, and it is required that e and The greatest common divisor of

[0019]

[0020] Calculate the modulus x;

[0021] Calculate the decryption key d, and At this time, the public key is (e,x) and the private key is (d,x);

[0022] Use the public key (e, x) to encrypt the DES key K each time, using the formula Li = Ri-1 and Iterate 16 times to obtain L 16 and R 16 .

[0023] As a preferred solution of the data encryption transmission method for the smart grid platform of distributed energy access described in the present invention, wherein: the modulus is expressed as,

[0024] If q <p,(n-p)<x<n,GCD(x,n)=1;

[0025] If q>p, (nq) <x<n,GCD(x,n)=1。

[0026] As a preferred solution of the data encryption transmission method for the smart grid platform of distributed energy access described in the present invention, wherein: the 16 decryptions of the DES subkey include reversely replacing the IP-1 of the ciphertext C by the DES algorithm to obtain L 16 and R 16 ;

[0027] Decrypt Ki (i=16,15,14,…,1) using the private key (d,x) of the RSA algorithm;

[0028] The obtained K is used in the DES algorithm to participate in the formula Li = Ri-1 and Get L0 and R0;

[0029] The obtained L0 and R0 are used to replace IP and restored to the original plaintext data M.

[0030] As a preferred solution of the data encryption transmission method for the smart grid platform connected to distributed energy resources of the present invention, wherein: the decryption to obtain the sender's plain text includes inputting a prime number to generate a key;

[0031] Encrypt the plaintext using the key and return the ciphertext;

[0032] Decrypt the ciphertext using the key and return the plaintext;

[0033] C represents a set of operations in the plaintext space, denoted by C{+};

[0034] For the input data Cn (n = 1, 2, 3, ...), encrypt the data Cn and convert it into the ciphertext space to obtain the ciphertext operation result. represents addition homomorphic processing, then

[0035] Another object of the present invention is to provide a data encryption transmission system for a smart grid platform with distributed energy access, which can solve the problem of insufficient security in existing smart grid data transmission and the susceptibility of data to attack and tampering during sharing and transmission by constructing a data encryption transmission system for a smart grid platform with distributed energy access, thereby improving the security and efficiency of data transmission.

[0036] To solve the above technical problems, the present invention provides the following technical solutions: a data encryption transmission system for a smart grid platform with distributed energy access, comprising: a plaintext encryption module, a key encryption module, a data decryption module and a homomorphic encryption module; the plaintext encryption module is used to encrypt plaintext data through the DES algorithm; the key encryption module is used to encrypt the DES subkey 16 times with a public key through the RSA algorithm; the data decryption module is used to decrypt the DES subkey 16 times with a private key through the RSA algorithm; the homomorphic encryption module is used to decrypt and obtain the sender's plaintext.

[0037] A computer device includes a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the steps of the data encryption transmission method for a smart grid platform with distributed energy access as described above are implemented.

[0038] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the data encryption transmission method for a smart grid platform with distributed energy access as described above.

[0039] Beneficial effects of the invention: The data encryption transmission method for the smart grid platform with distributed energy access provided by the invention is based on the characteristics of the RSA algorithm, and is improved on the basis of the original two moduli. The direct correlation between the length of large prime numbers and security in the RSA algorithm is utilized, and the calculation process is kept unchanged on the basis of increasing the modulus, that is, the length of the large prime number is increased, and the generation of the large prime number is improved, which greatly improves the security of the algorithm.

[0040] Since changing the modulus of the RSA algorithm leads to a relatively low efficiency of the algorithm encryption process, the DES algorithm is combined with the RSA algorithm for encryption based on the fast encryption speed of the DES algorithm. The DES algorithm based on the chaotic sequence (chaotic system) can keep the encryption key dynamic, thereby achieving one-time one-key. Even if a hacker obtains a set of keys in the channel, it is difficult to deduce the remaining keys based on this, thereby ensuring the security of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0042] Figure 1 An overall flow chart of a method for encrypting and transmitting data on a smart grid platform for access to distributed energy sources provided by an embodiment of the present invention.

[0043] Figure 2 A comparison chart of security and efficiency of different prime numbers selected for a data encryption transmission method for a smart grid platform with distributed energy access provided by an embodiment of the present invention.

[0044] Figure 3 An overall structural diagram of a data encryption transmission system for a smart grid platform with distributed energy access provided by an embodiment of the present invention.

[0045] Figure 4 An experimental comparison diagram of a data encryption transmission method for a smart grid platform with distributed energy access provided by an embodiment of the present invention.

[0046] Figure 5 Another experimental comparison diagram of the data encryption transmission method for the smart grid platform with distributed energy access provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0047] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.

[0048] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0049] Example 1

[0050] Reference Figure 1-Figure 2 , which is an embodiment of the present invention, provides a data encryption transmission method for a smart grid platform with distributed energy access, comprising:

[0051] Step 1. Encrypt plaintext data using the DES algorithm:

[0052] Step 1.1 For the plaintext data M, the sender first uses the DES algorithm to replace the IP of the encrypted data, and at the same time divides the encrypted data units into L0 and R0 respectively;

[0053] Step 1.2 Use the iterative formula to calculate 16 times to get L 16 and R 16 ; L0 R0 L16 R16 can be obtained based on the previous L0 and R0, and is an encrypted data unit that iterates 16 times

[0054] Step 1.3L 16 and R 16 Perform IP inverse permutation to obtain the ciphertext M. The specific expression is as follows:

[0055] F DES =P'-1×T 16 ×T 15 ×…×T1×P'

[0056] Where: P' is the initial transformation, P'-1 is the inverter of P', both satisfy IP'×IP'-1=1, and T is the number of encoding operation rounds. This is the inverse permutation formula. 16 To encode the number of operation rounds, it can be inferred from T.

[0057] Step 2. Encrypt the DES subkey 16 times with the public key using the RSA algorithm:

[0058] RSA algorithm before improvement:

[0059] Select two large prime numbers a and b, and a≠b, f=a×b,

[0060] Select a constant g such that g satisfies 1 <g<f;

[0061] Use (g,f) as the public key to encrypt the plaintext;

[0062] For private key Perform calculations and decryption operations on the ciphertext.

[0063] In the above steps, g and f are both public, but It is a key and needs to be kept secret. After being obtained, the security of the RSA algorithm will be greatly weakened. Therefore, the security of the RSA algorithm is directly related to the length of a and b. The longer the length of a and b, the higher the security. Similarly, the security of the RSA algorithm is also strongly related to the model of large prime numbers. The present invention adds multiple moduli on the basis of the unchanged algorithm, that is, increases two to four, so that the number of moduli is increased while increasing the length of the prime number.

[0064] Specifically, the improved RSA algorithm is as follows:

[0065] Step 2.1 Key generation;

[0066] Step 2.2 Randomly select four arbitrary large prime numbers p, q, r, and s, calculate n = pqrs and the Euler's totient function This step adds a modulus based on the original RSA algorithm, increasing the number of large prime numbers from two to four;

[0067] Step 2.3 Find a positive integer e that satisfies and require that the greatest common divisor of e and is

[0068] Step 2.4 Calculate the modulus x, and the calculation steps are as follows:

[0069] If q < p, then define x: (n - p) < x < n, GCD(x, n) = 1;

[0070] If q > p, then define x: (n - q) < x < n, GCD(x, n) = 1;

[0071] Step 2.5 Calculate the decryption key d, and At this time, the public key is (e, x), and the private key is (d, x);

[0072] Step 2.6 Use the public key (e, x) to encrypt the DES key K each time (a total of 16 times), and then use the formulas Li = Ri-1 and Iterate 16 times to obtain L 16 and R 16 .

[0073] As Figure 2 shown, the advantages and disadvantages of the improved RSA algorithm are relatively significant. Its advantage is high security performance. However, due to the increase in the modulus of large prime numbers, the length of the prime numbers increases, resulting in very low encryption efficiency and long time consumption. Therefore, on the basis of encrypting and decrypting keys using the RSA algorithm, DES is used to encrypt and decrypt the ciphertext.

[0074] Send the obtained ciphertext C and the DES sub-keys Ki (i = 1, 2, 3,..., 16) to the receiver for decryption after receiving the ciphertext.

[0075] Step 3. Decrypt the DES sub-keys 16 times using the private key through the RSA algorithm:

[0076] This step performs ciphertext decryption and key decryption simultaneously:

[0077] Step 3.1 During the decryption process, first use the DES algorithm to reversely replace the IP-1 of the ciphertext C to obtain L 16 and R 16 ;

[0078] Step 3.2: Decrypt Ki (i=16,15,14,…,1) using the private key (d,x) of the RSA algorithm;

[0079] Step 3.3 Use the DES algorithm to add the obtained K into the formula Li = Ri-1 and Get L0 and R0;

[0080] Step 3.4 replaces IP with the obtained L0 and R0 and restores the original plaintext data M.

[0081] The principle of DES symmetric encryption algorithm is to use substitution, transposition and shielding to achieve 16 iterations. Although the encryption speed is fast, its security cannot be guaranteed. Therefore, the public key of RSA is used to encrypt plaintext, and the private key is used to decrypt ciphertext. Symmetric encryption algorithm has high encryption efficiency but cannot achieve absolute security during use. Therefore, the advantages of both (RSA algorithm encrypts the key of DES) can be combined to achieve safer and more efficient transmission.

[0082] Step 4. Decrypt to get the sender’s plaintext:

[0083] The above encryption is performed for data units. When the data type for the power grid platform is a data set, the above key generation calculation, encryption and decryption process is similarly adopted. The ciphertext decryption process is improved and the ciphertext is homomorphically calculated. The calculation process is as follows:

[0084] First, input a prime number to generate a key; use the key to encrypt the plaintext and return the ciphertext; use the key to decrypt the ciphertext and return the plaintext; assume that C represents an operation set in the plaintext space, denoted by C{+}. Assume that for the input data Cn (n=1,2,3,…), first encrypt the data Cn and convert it to the ciphertext space to obtain the ciphertext operation result, and use represents addition homomorphic processing, then By analogy, the corresponding plaintext calculation result can be obtained by calculating the ciphertext and decrypting the result.

[0085] Example 2

[0086] Reference Figure 2 , which is an embodiment of the present invention, provides a data encryption transmission system for a smart grid platform with distributed energy access, including:

[0087] Plaintext encryption module, key encryption module, data decryption module and homomorphic encryption module;

[0088] The plaintext encryption module is used to encrypt plaintext data using the DES algorithm;

[0089] The key encryption module is used to encrypt the DES subkey 16 times with the public key through the RSA algorithm;

[0090] The data decryption module is used to decrypt the DES subkey 16 times using the private key through the RSA algorithm;

[0091] The homomorphic encryption module is used to decrypt and obtain the sender's plaintext.

[0092] Example 3

[0093] An embodiment of the present invention is different from the first two embodiments in that:

[0094] If the functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the methods described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc., which can store program codes.

[0095] The logic and / or steps represented in the flowchart or otherwise described herein, for example, may be considered as an ordered list of executable instructions for implementing logical functions, and may be embodied in any computer-readable medium for use by an instruction execution system, apparatus, or device (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, apparatus, or device and execute instructions), or in conjunction with such instruction execution system, apparatus, or device. For purposes of this specification, "computer-readable medium" may be any device that can contain, store, communicate, propagate, or transmit a program for use by an instruction execution system, apparatus, or device, or in conjunction with such instruction execution system, apparatus, or device.

[0096] More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection with one or more wirings (electronic devices), a portable computer disk case (magnetic devices), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), a fiber optic device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be a paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, deciphering, or processing in another suitable manner as necessary, and then stored in a computer memory.

[0097] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, a plurality of steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0098] Example 4

[0099] Reference Figure 4-Figure 5 , which is an embodiment of the present invention, provides a data encryption transmission method for a smart grid platform with distributed energy access. In order to verify the beneficial effects of the present invention, scientific demonstration is carried out through economic benefit calculation and simulation experiments.

[0100] Files of different types and sizes are treated as plain text data, including text files, image files, audio files, etc., covering small, medium and large data sizes, such as several files of 1KB, 10MB, and 100MB. The name, type, size and other information of each file are recorded.

[0101] Encryption and decryption programs using the traditional DES algorithm, the traditional RSA algorithm (two large prime numbers), and the RSA algorithm combining DES and four large prime numbers. To ensure the correctness and stability of the program, you can use a mature encryption library or the encryption module that comes with the programming language for development.

[0102] Select a computer with stable performance as the experimental platform, and record the computer's hardware configuration (such as CPU, memory, hard disk, etc.) and operating system information.

[0103] The prepared plaintext data are encrypted and decrypted using the traditional DES algorithm and the traditional RSA algorithm respectively; for each file, the encryption time, decryption time, key length and other data are recorded; the experiment is repeated multiple times and the average value is taken to improve the accuracy of the data.

[0104] Use the RSA algorithm that combines DES and four large prime numbers to encrypt and decrypt the same plaintext data; record data such as RSA key generation time, DES key encryption time, file encryption time, file decryption time, and total key length; repeat the experiment multiple times and take the average value.

[0105] Experimental data such as Figure 4 and Figure 5 As shown in the figure. For the traditional DES algorithm, the encryption and decryption time is relatively short. As the file size increases, the time increases linearly, but the growth rate is relatively slow.

[0106] The encryption and decryption time of the traditional RSA algorithm (two large prime numbers) is significantly longer than that of the traditional DES algorithm, and the time increases rapidly as the file size increases;

[0107] The RSA algorithm combining DES and four large prime numbers increases the computational complexity, but its growth trend is relatively stable as the file size increases.

[0108] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for encrypting and transmitting data on a smart grid platform with distributed energy access, characterized in that: include: Encrypt plaintext data using the DES algorithm; The DES subkey is encrypted 16 times with the public key through the RSA algorithm; Decrypt the DES subkey 16 times using the private key through the RSA algorithm; Decrypt to get the sender's plaintext.

2. The method for encrypting and transmitting data on a smart grid platform for access to distributed energy as claimed in claim 1, characterized in that: The encrypted plaintext data includes replacing the IP of the encrypted data using the DES algorithm, and the encrypted data units are L0 and R0 respectively; Using the iterative formula to calculate 16 times, we can get L 16 and R 16 ; For L 16 and R 16 Perform IP inverse permutation to obtain the ciphertext M.

3. The method for encrypting and transmitting data of a smart grid platform for distributed energy access as claimed in claim 2, characterized in that: The IP inverse permutation is expressed as, F DES =P' -1 ×T 16 ×T 15 ×…×T1×P' Where P' represents the initial transformation, P' -1 Inverter representing P', satisfying IP'×IP' -1 =1, T represents the number of encoding operation rounds.

4. The method for encrypting and transmitting data of a smart grid platform for access to distributed energy as claimed in claim 3, characterized in that: The 16-fold encryption of the DES subkey includes key generation; Randomly select four arbitrary large prime numbers p, q, r and s, and calculate n = pqrs and Euler function Seek a satisfaction A positive integer e, and it is required that e and The greatest common divisor of Calculate the modulus x; Calculate the decryption key d, and At this time, the public key is (e,x) and the private key is (d,x); Use the public key (e, x) to encrypt the DES key K each time, using the formula L i =R i -1 and Iterate 16 times to obtain L 16 and R 16 .

5. The method for encrypting and transmitting data on a smart grid platform for access to distributed energy as claimed in claim 4, characterized in that: The modulus is expressed as, If q <p,(n-p)<x<n,GCD(x,n)=1; If q>p, (nq) <x<n,GCD(x,n)=1。 6. The method for encrypting and transmitting data on a smart grid platform for access to distributed energy sources as claimed in claim 5, characterized in that: The 16 decryptions of the DES subkey include reversely replacing IP-1 of the ciphertext C by the DES algorithm to obtain L 16 and R 16 ; Decrypt K using the private key (d, x) of the RSA algorithm i (i=16,15,14,…,1); Use the DES algorithm to add the obtained K to the formula L i =R i -1 and Get L0 and R0; The obtained L0 and R0 are used to replace IP and restored to the original plaintext data M.

7. The method for encrypting and transmitting data on a smart grid platform for access to distributed energy sources as claimed in claim 6, characterized in that: The decryption to obtain the sender's plaintext includes inputting a prime number to generate a key; Encrypt the plaintext using the key and return the ciphertext; Decrypt the ciphertext using the key and return the plaintext; C represents a set of operations in the plaintext space, denoted by C{+}; For the input data C n (n=1,2,3,…), for data C n Encrypt and convert it into ciphertext space to obtain the ciphertext operation result. represents addition homomorphic processing, then 8. A system using the method for data encryption and transmission of a smart grid platform for access to distributed energy as claimed in any one of claims 1 to 7, characterized in that: include: Plaintext encryption module, key encryption module, data decryption module and homomorphic encryption module; The plaintext encryption module is used to encrypt plaintext data using the DES algorithm; The key encryption module is used to encrypt the DES subkey 16 times with the public key through the RSA algorithm; The data decryption module is used to decrypt the DES subkey 16 times using the private key through the RSA algorithm; The homomorphic encryption module is used to decrypt and obtain the sender's plaintext.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method for encrypting and transmitting data of a smart grid platform for access to distributed energy sources as described in any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method for encrypting and transmitting data of a smart grid platform for access to distributed energy sources as described in any one of claims 1 to 7 are implemented.

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